A Reproducible Standard Substrate in Starch-amylase Viscosimetry

A viscosimetric method of estimating enzyme concentration with special reference to amylase has been discussed in another communication 1 from this laboratory; and, in a later report, * the effects of variation in the concentration of starch from the standard lot and variation in lot of prepared soluble starch have been contrasted, indicating that only within a small range of variation of p (defined there as the relative viscosity of the blank with respect to water) may comparability of digestion rates be expected. These experiments were completed in June, 1930, but were not published at that time. The object was to demonstrate some of the difficulties (a subject treated also by Chesley) 3 which may be encountered in attempts to compare results with different lots of soluble starch in the hope that some method of obtaining reproducible standard substrate solutions might be suggested. In the present communication we propose to outline a method of approximating the 3 per cent starch solution previously suggested as a standard 2 by use of a composite of other lots of soluble starch. The experimental procedure involved simply the mixing of soluble starch of two original lots (one yielding a more viscous and the other a less viscous solution than the standard, if preparation was made in standard manner I, ~) in such proportion as to give a composite approximating the standard with respect to the value of p obtained from the conventional blank, 1 part of 0.85 per cent NaC1 added to 5 parts by volume of a 3 per cent starch solution prepared in the standard manner, at 37.50 ±0.03°C. t Thompson, W. R., Johnson, C. E., and Hussey, R., J. Gen. Physiol., 1931-32, 15, 1. 2 Wies, C. H., and McGarvey, S. M., J. Gen. Physiol., 1932-33, 16, 221. 3 Chesley, L. C., J. Biol. Chem., 1931, 92, 171. 229