Analysis of heat inactivation curves of alkaline phosphatase isoenzymes in serum

The course of the decline in alkaline phosphatase activity during exposureof serum samples to a temperature of 56 degree C can be resolved into two phases. These represent the exponential decay of an enzyme component with an average half-inactivation time of 112 seconds and of a second component with an average half-inactivation time of 456 seconds. The more rapid fall is due to inactivation of bone alkaline phosphatase and the slower to inactivation of liver and, when present, intestinal phosphatases. The half-inactivation times of the different enzyme species show considerable variation from one serum sample to another. The implications of this variation for methods of estimating the relative proportions of alkaline phosphatase isoenzymes by selective inactivation procedures are discussed.

A distinctive fraction of alkaline phosphatase in health and disease

An electrophoretic fraction of plasma alkaline phosphatase, which migrates more slowly than the main fraction, was present in one fifth of normal subjects, and in some patients with parenchymal liver disease. It was absent in patients with bone disease, uncomplicated biliary obstruction, and hepatic metastases. The electrophoretic and inhibition properties of this slow band were similar to those of intestinal phosphatase, and its significance is discussed. In a patient with hypophosphatasia this fraction was apparently not decreased.