Publisher Summary Isoenzyme refers to a biochemically distinct class of catalytically active proteins with the same specificity of bond cleavage or alteration, which can occupy several zones following electrophoresis. The chapter focuses on the mechanism of catalysis and uncompetitive inhibition and provides analyses of studies reporting distinctive immunochemical properties as well as physical properties of enzymes prepared from several organs. In the case of alkaline phosphatase, the studies rely on a combination of organ source, biochemical properties, and electrophoretic distinctions as guidelines for working in this field. Placental alkaline phosphatase is an isoenzyme of alkaline phosphatase, which can be distinguished from other alkaline phosphatases by biochemical means. The different molecular forms of this isoenzyme, which can be produced and separated by physical means, are referred as variants of placental alkaline phosphatase. Hyperphosphatasemia in diseases of liver and bone has made the serum alkaline phosphatase determination the most frequently demanded enzyme assay.

Isoenzymes of Human Alkaline Phosphatase

During the last 20 years, extensive efforts have been made by many workers to purify and crystallize alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC. 3.1.3.1 ) from bacterial, animal and human sources. Notable success has been achieved in this area by a number of investigator~.l-~~ In 1964, Malamy and H ~ r e c k e r ~ ~ made a major breakthrough in this field by crystallizing alkaline phosphatase for the first time from E. Coli (FIGURE 1 ) . Human placenta and intestine have long been known to possess alkaline phosphatase activity. Moss and his coworker^^^^^ used human intestinal tissue to purify alkaline phosphatase. The earliest report in which human placenta was shown to exhibit alkaline phosphatase activity appeared about three decades ago2* and was reconfirmed later.29 In recent years, a revived interest has been centered around human placenta, especially in the attempt to elucidate the mechanism of elevation of serum alkaline phosphatase level in pregnancy. In 1957, Anagnostopoulos and Matsudaira4 recognized placenta as a very rich source of alkaline phosphatase and initiated studies on the partial purification of the enzyme. In 1960, Ahmed and King30 made considerable advances in purification and were successful in obtaining reasonably pure alkaline phosphatase from this tissue. In the present work, methods of purifying human placental alkaline phosphatase have been reinvestigated. Attention has been focused on the existence of multiplicity in the molecular forms of human placental alkaline phosphatase on the basis of their molecular weights. Current studies, therefore, relate to the preparation of placental alkaline phosphatase variant at a very high state of purity and in homogeneous condition, to properties of the purified molecular weight variants, to comparison of the biochemical behaviors of placental and intestinal enzymes, to the mechanism of Lphenylalanine inhibition of the two isoenzymes and to characterization of the “placental type” alkaline phosphatase in human pregnancy sera as well as in neoplastic pleural effusion. Finally, purified preparation of human placental alkaline phosphatase, a sialoglycoenzyme, is proven to exhibit viral hemagglutination inhibitory potency. MATERIALS AND METHODS

Ehrlich-Gomolka H

Papers

Acid and alkaline phosphatase in the placenta and amniotic fluid