Abstract
1. Serum alkaline phosphatase [EC 3. 1. 3. 1] was strongly inactivated by histidine during incubation at pH 8.0 and 45°; however, tryptic digestion of the serum strongly protected the enzyme against inactivation by histidine. In the absence of histidine, however, neither heat inactivation of the phosphatase nor the effect of trypsin [EC 3.4.21.4] was observed. Factors affecting the alkaline phosphatase inactivation were studied further.
2. The effect of trypsin on the histidine-induced heat inactivation differed consider-ably according to the tissue source of the enzyme, which suggests a possible method for distinguishing alkaline phosphatase isoenzymes.
