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Glycosidic bonds of the form discussed above are known as O-glycosidic bonds, in reference to the glycosidic oxygen that links the glycoside to the aglycone or reducing end sugar. In analogy, one also considers S-glycosidic bonds (which form thioglycosides ), where the oxygen of the glycosidic bond is replaced with a sulfur atom.
Pullulanase is also known as pullulan-6-glucanohydrolase (Debranching enzyme). Its substrate, pullulan, is regarded as a chain of maltotriose units linked by α-1,6- glycosidic bonds . Pullulanase will hydrolytically cleave pullulan (α-glucan polysaccharides).
A branching enzyme attaches a string of seven glucose units (with some minor variation to this number) to the carbon at the C-6 position on the glucose unit, forming the α-1,6-glycosidic bond. The specific nature of this enzyme means that this chain of 7 carbons is usually attached to a glucose molecule that is in position three from the non ...
In general, β-1,3 linkages are created by 1,3-beta-glucan synthase, and β-1,4 linkages are created by cellulose synthase. The process leading to β-1,6 linkages is poorly understood: although genes important in the process have been identified, not much is known about what each of them do. [9]
Phosphorylase can only cleave α-1,4-glycosidic bond between adjacent glucose molecules in glycogen but branches also exist as α-1,6 linkages. When phosphorylase reaches four residues from a branching point it stops cleaving; because 1 in 10 residues is branched, cleavage by phosphorylase alone would not be sufficient in mobilizing glycogen ...
Cyclodextrins have toroidal structures formed by 6–8 glucose residues. Amylodextrin is a linear dextrin or short chained amylose (DP 20-30) that can be produced by enzymatic hydrolysis of the alpha-1,6 glycosidic bonds or debranching amylopectin. Amylodextrin colors blue with iodine.
Glucanases can also catalyze transglycosylation, resulting in new β-glycosidic bonds between donor and acceptor saccharides. [1] This reaction, which has the same region- and stereo-specificity as the hydrolysis reaction, involves either the direct reversal of hydrolysis (known as condensation ) or kinetic control of a glycosyl donor substrate.
Lysozyme, which is found in tears and constitutes part of the body's innate immune system exerts its antibacterial effect by breaking the β-(1,4)-glycosidic bonds in peptidoglycan (see above). Lysozyme is more effective in acting against gram-positive bacteria , in which the peptidoglycan cell wall is exposed, than against gram-negative ...