Influence of certain electrolytes upon the course of the hydrolysis of soluble starch by malt amylase

The rate of formation of reducing sugar (maltose) from soluble starch by purified malt amylase of diastatic power equivalent to about 1,600 on Lintner's scale, both in neutral solution containing no added electrolyte and with the addition of regulated amounts of hydrochloric or phosphoric acid or of primary potassium phosphate, was investigated from the beginning of the reaction to completion or until the hydrolysis is no longer measurable.

When the activating electrolyte was added in such amount as to give optimum or nearly optimum concentration of hydrogen ion, the action of the enzyme was increased not only in the earlier stages but throughout the entire range investigated. The greater the concentration of enzyme the less the apparent favorable effect of the added electrolyte.

The same optimum hydrogen ion concentration, C_H1O^-4.4 (P_H ⁺4.4), was found to hold for each of the acid electrolytes tested and appears to hold throughout the course of the hydrolysis. (With neutralized starch substrate used in this laboratory the amount of acid or acid phosphate required for optimum activation is about half as much for one per cent. as for two per cent. starch.) When more than the optimum amount of acid was added the hydrolysis proceeded at less than the optimum rate throughout; when less, the initial rate was better sustained. This difference was most pronounced in the case of hydrochloric acid; less with phosphoric acid; least in the case of acid phosphate (“buffereffect”).

With initial concentrations of I per cent. soluble starch it was found that, throughout the first half of the hydrolysis, or up to a yield of half the theoretical amount of maltose, the rate of maltose formation from soluble starch was found to be proportional to the concentration of substrate (in the form of starch and dextrin) still remaining at any given time, at least in solutions containing avorable amounts of acid or acid phosphate.