The determination of serum amylase, with particular reference to the use of beta-amylose as the substrate.

The estimation of serum amylase by the saccharimetric method is based upon the digestion of a starch solution with serum followed by the determination of the reducing substances produced. Differences in numerical values obtained by modifications of the basic method may result from the use of various types of starch (l-3), from differences in the pH of the digestion mixture (l-3), and from variations in the sensitivity of the procedure ultimately used for the determination of the end-products of the reaction. Many of the usual alkaline copper reagents are not readily reduced by maltose. The starch solutions used as the substrate frequently hinder the smooth performance of the test. They tend to give cloudy filtrates following the precipitation of the plasma proteins and thereby interfere with the use of the photoelectric calorimeter for the estimation of the reducing substances. Starch also retrogrades and comes out of solution so that the substrate must be renewed frequently. Myers et al. (3) have overhome some of these difficulties by using a buffered starch solution and determining the reducing substances by the reduction of pi&c acid. The products of the digestion reduce this substance to a greater degree than they do either the Folin-Wu or the Benedict reagents (4). Myers et al. have, however, continued to use a starch substrate. It would seem desirable to use some substrate which would (1) be in a stable form so that it would not have to be prepared frequently, (2) would give clear filtrates with the usual protein precipitants, and (3) would have a low blank reducing value. It was thought that some fraction of starch might meet these requirements.