The mechanism of degradation of starch by amylases

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Abstract
I. The products of action of amylases on soluble starch at 15, 20 and 25% hydrolysis were subjected to alcoholic fractionation. [alpha]-malt amylase and pancreatic amylase produced some maltose but mainly "dextrins," whose reducing power varied from 11.4 to 23% as maltose according to the extent of hydrolysis. [beta]-amylases from malt and ungerrninated barley produced maltose in amts. nearly equivalent to the reducing power, and the alcohol-insoluble fraction closely resembled starch.[long dash]II. Kinetic expts. with [alpha], [beta] and mixed amylases and with starch, amyloamylose, erythroamylose, achroodextrin and [alpha]-amylodextrin as substrates led to the conclusion that both amylases hydrolyse most readily the same (non-[alpha]-amylodextrin) portion of starch, amounting to about 60%. [alpha]-amylodextrin was not attacked by [beta]-amylase except in the presence of, or after preliminary attack by [alpha]-amylase. van Klinkenberg''s suggestion that starch consisted of [alpha]- and [beta]-components which are specifically hydrolyzed by [alpha]- and [beta]-amylases, respectively, is not supported by these observations.-[long dash]III. When [alpha]-amylase (of malt or the pancreas) acted on starch, its components or partial degradation products always produced reducing dextrins and maltose giving [alpha]-mutarotation, with increasing proportions of [alpha]-maltose as the reaction proceeded. [beta]-amylasc of malt or ungerminated barley produced [beta]-maltose as the sole reducing product. The velocities of mutarotation of the reaction products of advanced hydrolyses with both enzymes agreed reasonably well with those observed for [beta]-maltose under similar conditions. The direction of mutarotation was characteristic of the enzyme and was independent of the substrate employed, whether it be starch, amyloamylose, erythroamylose (Samec), [alpha]-amylodextrin (Baker), degradation products of this, or glycogen.

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