VPB 112: General Veterinary Biochemistry (1+1)

DEXTRINS AND DEXTRANS

Dextrins

• These are substances (smaller fragments) formed during the course of hydrolytic cleavage of starch either by enzymes or by HCl.
• The polysaccharides, starch and glycogen are polymers of glucose. These polysaccharides are hydrolyzed by amylases. There are two types of amylases called α – amylase and  β- amylase. They are present in the secretions of saliva and pancreas.
• α - amylase, which is present in both animals and plants is an endoamylase that hydrolyzes randomly the interior α(1 4) glycosidic bonds of amylose and amylopectin to yield a mixture of glucose, maltose and dextrins.
• Both amylases can not hydrolyze the α (16) linkage. After the hydrolysis by amylase , highly branched dextrins are produced.
• On treatment with HCl, starch is converted to glucose. The following is the order of the production. Starch, which gives blue colour with iodine (negative for Benedict’s) is hydrolyzed to amylodextrin (violet colour with iodine), erythrodextrin (red colour with iodine) and achrodextrin (no colour with iodine), which gives Benedict’s positive.
• Another enzyme β - amylase is an exoamylase that catalyses the sequential hydrolysis from the non-reducing end of amylose or amylopectin to form maltose.

Dextran

• A storage polysaccharide in yeast and bacteria also contains glucose residues but differ from glycogen and starch by having α(16) linkage and occasionally α(12), α(13) and α(14) linkages, which depends on species. It is used as plasma extenders. It is insoluble in water. In the case of blood loss It is given intravenously to increase the blood volume. Synthetic dextrans are used in the chromatography for the fractionation of proteins.