Characterization of placental isoenzyme of alkaline phosphatase in human pregnancy serum

Abstract

Human placental alkaline phosphatase isoenzyme has been characterized in pregnancy serum by several biochemical criteria. The total serum alkaline phosphatase, its L-phenylalanine-sensitive moiety, heat inactivation, and the ratio of enzyme activity at pH 10.7 versus 9.8 (10.7/9.8 R) were measured during parturition and 59 weeks of pre- and post-natal periods. The extent of L-phenylalanine inhibition, heat stability, and 10.7/9.8 R of serum alkaline phosphatase progressively increased during gestation attaining maximum values during the delivery, after which they gradually declined. The electrophoretic behaviors of alkaline phosphatase isoenzymes of pregnancy sera were followed by starch- and Sephadex-gel electrophoreses. Alkaline phosphatase has been purified 300-fold from the placenta of the subject whose serum enzyme was investigated. The biochemical properties, including the electrophoretic behavior and neuraminidase sensitivity of heat-stable alkaline phosphastase in pregnancy sera at term, were comparable to those of purified placental alkaline phosphatase. The values for 10.7/9.8 R of the pregnancy sera were statistically different from those of sera from normal nonpregnant women. The results obtained in this study suggest that the enhanced level of pregnancy serum alkaline phosphatase is due to the enrichment of the circulation with an isoenzyme of placental origin.