Biochemical Studies on Alkaline Phosphatases of Tissues

This section of the chapter is divided into six parts dealing in turn with kinetics, isoenzyme isolation, immunochemical and electrophoretic properties, heat sensitivity, and neuraminidase action. The purpose is to bring to the reader our present state of knowledge of those basic biochemical and biophysical properties that relate specifically to isoenzymes and their recognition. 

Although a considerable literature records numerous studies in this field (A19, B17, C12, J3, L9, P16, S4, S5), many have been performed on preparations of tissues from other than human sources. In conformity with the subject of this chapter and to avoid species differences, most attention will be directed to human tissue alkaline phosphatases and in particular their variants. The stereospecific L-phenylalanine inhibition has provided the impetus to study its molecular mechanism, which necessarily requires an understanding of the mechanism of catalysis. It is expected that discovery of other stereospecific inhibitors will follow and that they may have even greater utility than L-phenylalanine. However, since it is the first such unique inhibitor, this section of the chapter will receive extensive treatment after a consideration of some basic kinetic information. 

The alkaline phosphatase activity under consideration is that of a monophosphohydrolase (International Enzyme Classification 3.1.3.1). 

A degree of organ specificity for substrate is to be expected. Thus, a substrate preference known is the ability of intestinal alkaline phosphatase to hydrolyze o-carboxyphenylphosphate more rapidly than other substrates (Fll, F13). Further, placental alkaline phosphatase is stated to hydrolyze p-nitrophenyl phosphate less rapidly than j8-glycerophos-phate (SI). Although ethanolamine phosphate is hydrolyzed preferentially by rat liver alkaline phosphatase, such a preference was missing from human liver preparations (Fll). 

The use of two substrates plus a specific inhibitor can be of great value in identifying organ-specific isoenzymes, as shown by Green et al. (G16) 

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