Maltose

Pocket-sized Intestine

Courtney Thou. Townsend JR., Physician , in Sabiston Textbook of Surgery , 2022

Carbohydrates

An developed consuming a normal Western diet volition ingest 300 to 350 g of carbohydrates a day, with about 50% consumed every bit starch, 30% equally sucrose, half-dozen% as lactose, and the rest as maltose, trehalose, glucose, fructose, sorbitol, cellulose, and pectins. iii Dietary starch is a polysaccharide consisting of long chains of glucose molecules. Amylose makes up about 20% of starch in the diet and is cleaved down at the α-1,4 bonds by salivary (i.e., ptyalin) and pancreatic amylases that convert amylose to maltotriose and maltose. Amylopectin constitutes about fourscore% of dietary starch and has co-operative points every 25 molecules along the directly glucose chains; the α-1,half-dozen glucose linkages in amylopectin identify the stop products of amylase digestion—maltose, maltotriose, and the balance co-operative saccharides, the dextrins. In full general, the starches are almost totally converted into maltose and other small glucose polymers before they reach the duodenum or upper jejunum. The residue of carbohydrate digestion occurs every bit a upshot of castor border enzymes of the luminal surface.

The brush edge of the small intestine contains the enzymes lactase, maltase, sucrase-isomaltase, and trehalase, which carve up the disaccharides equally well as other small glucose polymers into their constituent monosaccharides (Table 50.one). Lactase hydrolyzes lactose into glucose and galactose. Maltase hydrolyzes maltose to produce glucose monomers. Sucrase-isomaltase is a complex with two subunits; sucrase hydrolyzes sucrose to yield glucose and fructose, and isomaltase hydrolyzes the α-1,6 bonds in α-limit dextrins to yield glucose. Glucose represents more than lxxx% of the concluding product of saccharide digestion, with galactose and fructose normally representing no more 10% of the products of carbohydrate digestion.

Carbohydrates are captivated as monosaccharides. Transport of the released hexoses (glucose, galactose, and fructose) is by specific mechanisms involved in active send. The major routes of assimilation are past three membrane carrier systems (Fig. fifty.5): sodium-glucose transporter ane (SGLT-one), glucose transporter five (Glut-5), and glucose transporter 2 (GLUT-2). iii Glucose and galactose are absorbed by a carrier-mediated active transport mechanism, which involves the cotransport of sodium (SGLT-1 transporter). As sodium diffuses into the within of the jail cell, information technology pullsthe glucose or galactose along with it, thus providing the energy for transport of the monosaccharide. The leave of glucose from the cytosol into the intracellular infinite is achieved predominantly past a sodium-contained carrier (Glut-2 transporter) located at the basolateral membrane of enterocytes. Fructose, the other significant monosaccharide, is besides absorbed from the intestinal lumen through facilitated diffusion. This carrier, GLUT-5, is located in the apical membrane of the enterocytes. In contrast to SGLT-1, this transport process does non depend on sodium or free energy. Fructose exits the basolateral membrane by another facilitated diffusion process involving the Glut-2 transporter.

Enzymes, Industrial (overview)

B.C. Saha , ... R.J. Bothast , in Encyclopedia of Microbiology (Third Edition), 2009

Production of Loftier-Maltose Conversion Syrups

Diverse maltose-containing syrups are used in the brewing, baking, soft drink, canning, confectionery, and other nutrient industries. There are three types of maltose-containing syrups: loftier-maltose syrup (DE 35–50, 45–60% maltose, 10–25% maltotriose, 0.5–three% glucose), extra high-maltose syrup (DE 45–threescore, 70–85% maltose, 8–21% maltotriose, 1.five–two% glucose), and loftier conversion syrup (DE 60–seventy, 30–47% maltose, 35–43% glucose, 8–fifteen% maltotriose). Production of these syrups from starch by and large involves liquefaction and saccharification, as in the production of glucose. However, in this process, the liquefaction reaction is terminated when the DE reaches about 5–10 since a low DE value increases the potential for attaining high maltose content. Depending on the maltose content of the syrup desired, saccharification is generally performed by using a maltogenic amylase such as β-amylase, β-amylase with pullulanase or isoamylase, or a fungal α-amylase at pH v.0–5.5 and 50–55  °C. High conversion syrups are produced from liquefied starch (DE, generally 40) by saccharification with a carefully balanced mixture of β-amylase or fungal α-amylase and glucoamylase. After fractional saccharification, the syrup is heated to destroy the enzyme action and prevent farther glucose germination.

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Digestion and Absorption of Carbohydrate, Protein, and Fat

Marking Feldman MD , in Sleisenger and Fordtran's Gastrointestinal and Liver Illness , 2021

Membrane Digestion

The products of the luminal digestion of starch and glycogen past salivary and pancreatic amylases, along with the disaccharides sucrose and lactose nowadays in diet form the substrates for membrane digestion, which occurs on the external surface of the BBM of the abdominal absorbent cells (Fig. 102.4). At least 4 enzymes are involved in membrane digestion: maltase-glucoamylase, sucrase-isomaltase, lactase, and trehalase; all of them are integral proteins in the BBM with their catalytic sites exposed to the luminal surface of the membrane so that their corresponding intraluminal substrates have access to the agile site. Maltase-glucoamylase hydrolyzes maltose and malto-oligosaccharides to generate free glucose. Sucrase-isomaltase is a bifunctional enzyme with 2 catalytic sites (i.due east., sucrase and isomaltase) that reside in different parts of the same protein. However, though the enzyme is initially synthesized as a single polypeptide that gets inserted into the BBM, it is subsequently cleaved by pancreatic proteases into 2 subunits, one with sucrase activity and the other with isomaltase activity. 38 The sucrase component of the enzyme is responsible for the digestion of sucrose into glucose and fructose, and also for the digestion of maltose into glucose. The isomaltase component of the enzyme is selective for the α-one,6 glycosidic bond nowadays in α-limit dextrins. As the α-ane,6 glycosidic bond is nowadays simply at branch points in α-limit dextrins, its hydrolysis by isomaltase results in debranching of α-limit dextrins subsequently which maltase-glucoamylase and sucrase act on the resultant maltose and other linear malto-oligosaccharides to generate gratuitous glucose. Lactase acts on the milk carbohydrate lactose to release glucose and galactose. Trehalase breaks down trehalose to generate glucose. Interestingly, mRNAs are institute for all of these brush-edge carbohydrases in the epithelial cells in the crypts, as well as in the upper parts of the villus, indicating that transcription of the respective genes occurs throughout the villi the states, but the enzyme proteins are found more often than not in differentiated epithelial cells of the upper villi us. As the luminal contents containing the products of salivary and pancreatic amylases (maltose, maltotriose, and α-limit dextrins) and other dietary disaccharides have access simply to the upper parts of the villi and do not generally reach the crypts, the presence of the enzymes mostly in the differentiated epithelial cells makes physiologic sense. With regard to the longitudinal distribution of these brush-edge enzymes, they are establish at much higher levels in the jejunum than in the ileum. Collectively, the BBM-associated carbohydrases bring almost the digestion of dietary carbohydrates to completion, releasing monomeric units of the polysaccharides and disaccharides present in the diet (seeFig. 102.4). The resultant monosaccharides (i.e., glucose, galactose, and fructose) are subsequently absorbed into enterocytes and then into portal blood.

Carbohydrate Structure

Larry R. Engelking , in Textbook of Veterinary Physiological Chemistry (Third Edition), 2015

Disaccharides and Trisaccharides

Disaccharides consist of ii monosaccharides joined by a glycosidic bond. Structures for the about common disaccharides are shown in Fig. eighteen-iv .

Maltose (or malt sugar) is an intermediate in the abdominal digestion (i.eastward., hydrolysis) of glycogen and starch, and is found in germinating grains (and other plants and vegetables). It consists of two molecules of glucose in an α-(1,iv) glycosidic linkage. Trehalose, which contains two molecules of glucose linked together somewhat differently from maltose, is a major carbohydrate found in the hemolymph of many insects. Information technology is besides found in immature mushrooms, where it accounts for about i.5% of their weight. Cellobiose, the repeating disaccharide unit of cellulose, has β-(1,4) glycosidic linkages which are cleaved by bacterial cellulases, merely not by mammalian constitutive digestive enzymes.

Lactose is found in milk, but otherwise does not occur in nature. Information technology consists of galactose and glucose in a β-(1,4) glycosidic linkage.

Sucrose, or cane carbohydrate, consists of glucose and fructose linked in an α-(1,two) glycosidic bond. It is abundant in the plant world, and is familiar as table carbohydrate. Sucrose and maltose are readily hydrolyzed by disaccharidases institute in the brush edge of the small intestine (see Chapter 38). Hydrolysis of sucrose to glucose and fructose is sometimes chosen inversion, since information technology is accompanied past a cyberspace change in optical rotation from dextro to levo as the equimolar mixture of glucose and fructose is formed on the mucosal surface. Therefore, the intestinal brush border enzyme that hydrolyzes sucrose (i.e., sucrase), is sometimes called invertase (see Chapter 38).

A number of trisaccharides also occur complimentary in nature, and are consumed by animals. Raffinose contains glucose, fructose, and galactose held together by both α- and β- glycosidic bonds. This trisaccharide is establish in abundance in carbohydrate beets, and several other higher plants. Melezitose contains two molecules of glucose and ane of fructose, and is found in the sap of some coniferous copse.

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Carbohydrates

Antonio Blanco , Gustavo Blanco , in Medical Biochemistry, 2017

Disaccharides

Disaccharides are formed by the bounden of two monosaccharides. This reaction produces a water molecule. But the well-nigh of import disaccharides in human biochemistry will exist mentioned here.

Maltose

Malt saccharide or maltose is a production of the hydrolysis of starch, catalyzed past the enzyme amylase. It is slightly sweet, very soluble in water, and results from the binding of carbon i of α- d-glucose (α-glycosidic bond) to carbon 4 of another d-glucose. Maltose is generated during brewing of beer and related beverages (malt beverages).

The aldehyde group of ane of the glucoses remains costless, giving the disaccharide its reducing properties and allowing it to have α and β forms.

Lactose

This disaccharide is institute in milk. When hydrolyzed, galactose and glucose are released. Carbon 1 of β-d-galactose (β-glycosidic bond) is jump to carbon 4 of d-glucose. Every bit carbon i of glucose remains free, lactose presents α and β forms and has reducing chapters.

*Name co-ordinate to current nomenclature. O indicates glucose C1 oxygen spring to C4 of the other.

Saccharose

This saccharide is commonly used as a sweetener in foods. It is obtained from saccharide pikestaff and beet. It consists of glucose and fructose, linked by a double glycosidic bond betwixt carbon one of α glucose and carbon 2 of β-fructose. Both groups, aldehyde and ketone, are blocked and the disaccharide does non have reducing characteristics.

Sucrose is dextrorotatory and subjected to hydrolysis produces an equimolar mixture of glucose and fructose, in which the levorotatory activeness of fructose predominates over the dextrorotatory activity of glucose. Due to this change in polarized calorie-free rotation, the mixture of glucose and fructose resulting from hydrolysis of sucrose is commonly known every bit "inverted saccharide." Honey contains inverted carbohydrate.

Cellobiose. This is a disaccharide that results from hydrolysis of cellulose. It is formed by two glucose units linked by a β-1→iv bond.

Trehalose. This is a nonreducing disaccharide composed of ii α-d-glucose molecules linked by their anomeric hydroxyls (α-d-glucopyranosyl-(1→1)-α-d-glucopyranoside).

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Carbohydrate Digestion, Assimilation, and Fiber

G. Livesey , in Reference Module in Biomedical Sciences, 2014

Linear Gluco-oligosaccharides (α1,iv-Dextrins from Starch)

Maltose, maltotriose, and college malto-oligosaccharides (having 2, iii, and >3 glucose units, respectively) are hydrolyzed by the small-scale-intestinal brush-border-anchored maltase–glucoamylase complex (Mag). Glucoamylase is an exo-enzyme – glucose is released 1 unit at a time from the nonreducing end of the glucose chain. MAG accounts for all glucoamylase action, although simply twenty% of maltase activity. Rarely, Mag deficiency is seen in infants who display chronic diarrhea later on starch ingestion, and it may be accompanied by sucrose and lactase deficiency.

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Immunoglobulins

In Meyler'south Side Furnishings of Drugs (Sixteenth Edition), 2016

Blood glucose measurement

Intravenous immunoglobulins containing maltose every bit a stabilizer tin can interfere with claret glucose monitoring in systems that use glucose dehydrogenase [ 242]. There is no interference with systems that apply glucose oxidase.

Falsely high blood glucose readings accept been attributed to interference by WinRho® SDF, an intravenous human being rhesus D immunoglobulin, or other maltose-containing intravenous immunoglobulin products when using systems that are not glucose-specific. The FDA released a condom warning near this issue for all maltose-containing intravenous immunoglobulins [243]. Some other case of imitation hyperglycemia induced by a maltose-containing immunoglobulin solution was reported where the monitoring device using the principle of bioamperometry created a falsely loftier blood glucose reading by interference from maltose in the claret [244].

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Gastrointestinal Function

William E. Hornbuckle , ... Bud C. Tennant , in Clinical Biochemistry of Domestic Animals (Sixth Edition), 2008

2 Disaccharide Digestion

Maltose and isomaltose are the disaccharides (glucose-glucose) produced as end products of starch digestion. The diet also may contain lactose (galactose-glucose) and sucrose (fructose-glucose). There is general understanding that disaccharide digestion is completed at the surface of the cell past disaccharidases ( Gray, 1975), which are components of the brush border (Table fourteen-6).

Tabular array 14-six. Enzymes of the Intestinal Castor Edge

Enzyme Substrate Product Reference
Lactase Lactose Glucose, galactose Alpers (1969), Forstner et al. (1968)
Sucrase Sucrose; 1,4% dextrins Glucose, fructose; residuum 1,6-oligosaccharides Grayness et al. (1979)
Isomaltase 1,6% Dextrins Glucose Grey et al. (1979), Rodriguez et al. (1984)
%-Limit dextrinase 1,6% Dextrins Glucose Taraval et al. (1983)
Trehalase Trehalose Glucose Eichholtz (1967), Nakano et al. (1977)
Enterokinase Trypsinogen Trypsin Grant and Herman-Taylor (1976)
Aminopeptidase A Acidic amino-terminal amino acids Acidic amino acids Benajiba and Maroux (1980)
Aminopeptidase N Neutral amino-terminal amino acids Neutral amino acids Kim and Brophy (1976), Erickson et al. (1983)
(-Glutamyl transferase) Peptides with (-glutamyl bonds) (-Glutamyl amino acids) Benajaba and Maroux (1980), Hughey and Curthoys (1976)
Element of group i phosphatase Phosphate esters Inorganic phosphate Eichholz (1967), Forstner et al. (1968)

The disaccharidases take been solubilized from the brush border and partially purified. Sucrase and isomaltase have been purified together as a two-enzyme complex (Gray et al., 1979; Kolinska and Semenza, 1967), and this enzyme complex accounts for the full hydrolysis of the products of amylase digestion (Gray et al., 1979; Rodriguez et al., 1984). The mutual mucosa contains two enzymes with lactase activeness. Ane of these is a nonspecific β-galactosidase that hydrolyzes synthetic β-galactosides effectively only hydrolyzes lactose at a slow rate. This enzyme has an optimal pH of iii and is associated with the lysosomal fraction of the cell. The other lactase hydrolyzes lactose readily, is associated with the brush edge fraction of the jail cell, and is the enzyme of primary importance in the digestive process (Alpers, 1969).

Maltase, isomaltase, and sucrase are almost completely absent from the intestine in newborn pigs (Dahlqvist, 1961) and calves. The activity of these disaccharidases increases after birth and reaches developed levels during the first months of life. Lactase activity is highest at birth and decreases gradually during the neonatal period. The relatively loftier lactase activity may exist an advantage to the newborn in utilizing the big quantities of lactose present in their diets. Bywater and Penhale (1969) demonstrated lactase deficiency post-obit acute enteric infections and suggested that lactose utilization may be decreased in such cases.

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Simple Carbohydrates

N.V. BHAGAVAN , in Medical Biochemistry (Fourth Edition), 2002

Disaccharides

Structures of some disaccharides are illustrated in Effigy nine-20.

Figure 9-20. Structures of some disaccharides. *Anomeric carbon atoms. All structures are Haworth projections.

Maltose is composed of two glucose residues joined by an α-glycosidic linkage between C1 of one residue and Civ of the other balance [designated α(1 → 4)]. In maltose. the second sugar residue has an unsubstituted anomeric carbon atom and therefore can function every bit a reducing amanuensis too as exhibit mutarotation. In trehalose, two glucose residues are joined by an α-linkage through both anomeric carbon atoms; therefore, the disaccharide is not a reducing saccharide, nor does it exhibit mutarotation. Lactose, synthesized only past secretory cells of the mammary gland during lactation, is a disaccharide consisting of galactose and glucose. The glycosidic bond is a β-linkage between Ci of galactose and Cfour of glucose (Figure 9-20). Lactose is a reducing sugar and exhibits mutarotation by virtue of the anomeric Cone of the glucose rest. Lactulose is a disaccharide consisting of galactose and fructose linked through a β-linkage between C1 of galactose and C4 of fructose. It is used in the treatment of some forms of chronic liver illness (such as hepatic encephalopathy) in which the ammonia content in the claret is elevated (hyperammonemia). Ordinarily, ammonia produced in the gastrointestinal tract, principally in the colon by microbial action, is transported to the liver via the portal circulation and inactivated by conversion to urea (Chapter 17). Oral administration of lactulose relieves hyperammonemia by microfloral conversion in the colon to a variety of organic acids (e.thousand., lactate) that acidify the colonic contents. Lactulose is neither broken down nor absorbed in the small intestine. Reduction of the colonic luminal pH favors conversion of ammonia (NH3) to ammonium ion NH 4 + , which is non easily absorbed, and thus its absorption is decreased. Reduction of luminal pH may additionally promote a microflora that causes a decrease in the product of ammonia likewise as an increase in its utilization. The osmotic action of the disaccharide and its metabolites causes an osmotic diarrhea, which is useful in eliminating toxic waste matter products.

Another nonabsorbable disaccharide used in the treatment of hepatic encephalopathy is lactitol (β-galactosidosorbitol). Compared to lactose, lactital has the advantage of higher palatability and fewer side effects (east.g., flatulence). Ammonia product in the colonic lumen by urease-producing bacteria can be reduced by administering antibiotics such as neomycin or metronidazole. The therapeutic event of the combined utilise of a nonabsorbable disaccharide and an antibiotic may result from the metabolism of the disaccharide by antibiotic-resistant bacteria.

Sucrose, a widely occurring disaccharide plant in many plants (cane sugar and beet sugar), consists of glucose and fructose moieties linked together through Ci of glucose and C2 of fructose. Sucrose is not a reducing sugar and does not mutarotate.

Because of its sweet taste sucrose is consumed in large amounts. The perception of sweet is mediated by taste buds submerged in the tongue and oral mucous membranes. The sense of taste bud, a pear-similar organ, consists of sensory cells (taste cells) interwoven with a branching network of nervus fibers. The taste bud contains two additional cell types: basal and supporting cells. Sensory cells have a short life span of about 10 days, and new cells are derived from basal cells that continually undergo mitosis. Sensory cells contain microvilli (thin hair-like projections on the surface of the cells). The microvilli protrude through the pores of the gustatory modality buds to provide a receptor surface for the perception of sense of taste. Highly soluble and diffusible substances, such as common salt (NaCl) and sugars, enter the taste pores and produce taste sensations. The chemic stimuli received by the sensory cells are transduced into electrical impulses. These impulses, in plough, are passed on to the nerve fibers through neurotransmitters. Less soluble and diffusible compounds, such as starch and protein, produce correspondingly less taste sensation.

The four primary taste sensations are sweetness, salty, bitter, and sour. Each taste bud possesses different degrees of sensitivity for all 4 qualities, merely it ordinarily has greatest sensitivity to one or two. The integration of sense of taste perception occurs in the cerebral cortex, which receives nerve signals arising from the sense of taste buds that pass through the medulla and the thalamus. An important function of gustation perception is to provide reflex stimuli that regulate the output of saliva. A pleasant taste perception increases saliva production, whereas an unpleasant sense of taste reduces output. Taste also affects the overall digestive process by affecting gastric contractions, pancreatic flow, and intestinal motion.

Choice of food and dietary habits are influenced past taste and odor, which are interrelated. The sense of scent resides in receptors of specialized bipolar neuronal cells (olfactory cells) located on each side of the upper region of the nasal crenel. Like taste sensory cells, the receptors of the olfactory cells with cilia protruding into the mucus roofing the epithelium, also undergo continuous renewal just with a longer turnover rate of about 30 days. The receptors of olfactory cells are stimulated by volatile airborne compounds. Since perceptions of taste and smell are triggered by chemicals, they are called chemosensory perceptions. At the molecular level, they are mediated past ionotropic channels and M protein coupled receptors (Chapter 30). Chemosensory perceptions are affected by a number of factors. Normal aging leads to perceptual as well every bit anatomical losses in chemosensory processes. Increased thresholds for both gustatory modality and smell accompany aging. For example, aged persons demand two to three times as much carbohydrate or common salt as young persons to produce the same degree of taste perception. The reduction in chemosensory vigil may contribute to weight loss and malnutrition in elderly persons. Other causes of chemosensory disorders include aberrations of nutrition and hormones, infectious diseases, treatment with drugs, radiation, or surgery. Sugars exhibit dissimilar degrees of sweet (Table 9-one). Sucrose is sweeter than the other common disaccharides, maltose and lactose. D-Fructose is sweeter than either D-glucose or sucrose. D-Fructose is manufactured commercially starting with hydrolysis of cornstarch to yield D-glucose, which is subsequently converted to D-fructose by the found enzyme glucose isomerase.

TABLE 9-1. The Relative Sugariness of Sugars, Saccharide Alcohols, and Noncarbohydrate Sweeteners

Type of Compounds Percent Sweetness Relative to Sucrose
Disaccharides
Sucrose 100
Lactose twenty
Maltose 30
Monosaccharides
Glucose 50–70
Fructose 130–170
Galactose thirty
Sugar alcohols
Sorbitol 35–60
Mannitol 45–sixty
Xylitol 200–250
Noncarbohydrate sweeteners
Saccharin 40,000
Aspartame 16,000

Synthetic noncarbohydrate compounds can too produce a sweet taste. Saccharin, a synthetic compound, tastes 400 times as sweetness every bit sucrose and has the following structure:

Another synthetic sweetener is aspartame (50-aspartyl-L-phenylalanine methyl ester), a dipeptide. Aspartame is 160 times equally sweetness as sucrose and, unlike saccharin, is said to have no palatableness. Artificial sweeteners, because of their loftier degree of sweetness on a weight-for-weight basis compared to sucrose, contribute very fiddling energy in human diet. They are useful in the management of obesity and diabetes mellitus. However, employ of aspartame during pregnancy, particularly past individuals heterozygous or homozygous for phenylketonuria (Chapter 17), may exist hazardous to the fetus.

The perception of sweet gustation tin can be elicited by a wide range of chemic compounds. Two naturally occurring sweet proteins, thaumatin and monellin, are derived from the fruits of two African plants called katemfe and serendipity berries, respectively. These two proteins are intensely sweetness and produce a perception of sweetness at a concentration every bit depression as 10−8 mol/Fifty. Despite the similarity in sweetness, thaumatin and monellin comport no significant structural similarities with respect to amino acid sequence or crystalline construction. However, they practice showroom immunological cross-reactivity suggesting a mutual chemical and structural characteristic. Sweet substances may act as shortterm antidepressants, presumably by raising serotonin (a metabolite of tryptophan) levels in the central nervous system. This property of sweet-tasting carbohydrates may unwittingly contribute to the development of obesity in susceptible individuals.

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RNA Modification Enzymes

Ethan S. Pickerill , Douglas A. Bernstein , in Methods in Enzymology, 2021

three.four Removal of nourseothricin resistance marker

Streak confirmed transformant onto Yeast Peptone Maltose (YPMaltose) (2% maltose) plates. Choice a colony from the streaked plate and culture yeast for 48  h at xxx   °C in liquid YPMaltose xx   thousand/L maltose. Plate 200–400 cells on YPMaltose twenty   g/L maltose and incubate at 30   °C for 24   h. Replica plate onto YPMaltose and YPMaltose 200   μg/mL nourseothricin. Incubate at 30   °C for 24   h. Note that colonies that no longer abound on YPMaltose 200   μg/mL nourseothricin, just grow on YPMaltose have lost the nourseothricin resistance marker, CaCAS9, and guide RNA. Save strains that accept lost Natr marker, CaCAS9, and guide RNA. Note that strains that accept lost the nourseothricin resistance marker, CaCAS9, and guide RNA tin can be subjected to additional rounds of CRISPR-Cas9 genome editing.

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