Amylopectin, reaction with

When the substrate was amylopectin (3-amylase limit dextrin, a different pattern of products was formed, namely Gl, G2 and G3, with no G6, G7 or higher sized dex-trins.14 Reaction with the (3-limit dextrin indicated that Gl, G2 and G3 are formed from the chains between the o-( 1 —6) branch linkages as the outer chains were removed by the action of (3-amylase (see Section 7.2 for a discussion of the action of (3-amylase). It further indicated that G6 and G7 from amylopectin were formed exclusively from longer unbranched outer chains. It also indicated that the number of glucosyl units between the branch linkages of amylopectin were sufficiently few that they could not yield the larger G6 and G7 products, but could give the smaller Gl, G2 and G3 products. 

Reactone dyes, which contain trichloropyrimidinyl groups, react with polysaccharides in an analogous way to chlorotriazinyl dyes, but the extent of reaction is somewhat less, at least in their reaction with cellulose. Reactone Red 2B derivatives of amylose, amylopectin, " starch, and barley )8-glucan provide substrates for amylases and y3-glucanases in the assay of these enzymes. 

Starches differ in their chemical composition and, except in rare instances, are mixtures of two structurally different polysaccharides, amylose and amylopectin. The proportions of these present in natural starches depend upon the source, although in most starches amylopectin is the main component, amounting to about 70-80 per cent of the total. An important qualitative test for starch is its reaction with iodine amylose produces a deep blue colour and amylopectin solutions produce a blue-violet or purple colour. 

The quantity of amylose may be determined in starches or other mixtures by a characteristic reaction with iodine. Amylose combines with iodine to form a deep-blue complex, which is responsible for the color of starch indicators. Amylopectin solutions are colored blue-violet or purple. The intensity of the amylose-iodine complex can be measured in a spectrophotometer, or titrimetric measurements can be made of the amount of iodine taken up in forming the amylose-iodine complex. 

A few other polysaccharides which have colour reactions with iodine, e.g. amylopectin and pectin B, also exhibit Cotton effects at about 600 nm. The weak peaks at about 350 nm are probably caused by iodine molecules associated outside the helix. 

Solutions of 1% (w/v) puUulan, amylose, amylopectin, mammalian glycogen, oyster glycogen and soluble starch (pH 6.0) were incubated at 60 C with purified enzyme (0.05 U/ml). Samples were withdrawn after 216 hrs and heated at lOO C for 15 min for enzyme inactivation. The reaction products were analyzed by HPLC for sugars. (12). (Reprinted with permissicm from Ref. 13. Copyright 1990 Academic Press, Inc.)... 

More specific hydrolysis may be achieved by the use of enzymes. Thus, the enzyme a-amylase in saliva and in the gut is able to catalyse hydrolysis of al 4 bonds throughout the starch molecule to give mainly maltose, with some glucose and maltotriose, the trisaccharide of glucose. Amylose is hydrolysed completely by this enzyme, but the al 6 bonds of amylopectin are not affected. Another digestive enzyme, a-l,6-glucosidase, is required for this reaction. Finally, pancreatic maltase completes the hydrolysis by hydrolysing maltose and maltotriose. 

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