A photometric method for the determination of alpha-amylase in blood and urine, with use of the starch-iodine color.

The use of the starch-iodine color for the estimation of ar-amylase appears to be on a sound theoretical basis. Swanson (1) has shown that in the degradation of amylose by a-amylase there is a random attack by the enzyme upon the polysaccharide chain yielding hexose units of varying lengths. Swanson (2) has further observed that chains 4 to 6 glucose units in length give no color with iodine, chains containing 8 to 12 units give a red color, and chains of 30 glucose units, or longer, yield a blue color. We have developed a starch-iodine method for the determination of a-amylase in serum and urine in which the blue color formed by the reaction of starch with iodine is measured photometrically before and after incubation of soluble starch with material containing the enzyme. The decrease in blue color obtained after the incubation is a measure of the amylase concentration. When appropriate conditions are set up, starch-iodine color values are obtained that are proportional to the amount of enzyme present and to the time of incubation, with use of a fairly wide range of concentration of substrate. The use of the photoelectric calorimeter removes the limitations inherent in starch-iodine methods in which an end-point is visually selected. In addition to being sound theoretically, the proposed method has certain practical advantages: It requires less work and time than the saccharogenic methods, the procedure is simple and is applicable to the estimation of amylase in blood and urine without change in the basic technique, and it permits the achievement of a high degree of accuracy and precision.