Lxx. the Mechanism of Degradation of Starch by Amylases. I. Nature of the Early Fission Products

OHLSSON [1926; 1930] concluded from experiments on the action of the "dextrinogenamylase" and "saccharogenamylase" of malt on starch that the former enzyme breaks starch into progressively smaller molecules until maltose is produced, whereas the latter enzyme detaches maltose molecules successively from the starch. This conclusion was based mainly on the relative permanence of the starch-iodine reaction during digestion by the respective enzymes at equal saccharifying concentrations. The argument is not wholly reliable, since the nature of the starch-iodine reaction is not understood, and it is not certain that colour is a function of molecular dimensions. Therefore an investigation has been made of the actual reducing products present in starch partly degraded by these and similar enzymes. As the dextrinogenamylase of malt is an oc-amylase [Ohlsson, 1930] in the sense that the products of its action on starch exhibit mutarotation in the oc-sense [Kuhn, 1925], this enzyme will be referred to herein as oc-malt-amylase. Similarly the saccharogenamylase, a /3-amylase, will be termed /-malt-amylase. The investigation is concerned with hydrolytic products at a comparatively early stage in the degradation of starch. A preliminary experiment showed that the velocity of hydrolysis of soluble starch by oc-malt-amylase in low concentration became inconstant at 15-20 % hydrolysis whilst at 25 % hydrolysis the iodine reaction had changed to red. Therefore stages corresponding to 15, 20 and 25 % hydrolysis were selected as likely to be informative. /3-Amylase from malt and from ungerminated barley showed no colour transition until the hydrolysis was too far advanced to be of use.