Inhibition of gamma-glutamyltranspeptidase by treatment of intact lymphocytes with periodate.

The plasma membrane contains some enzymes whose active sites face the external medium rather than the cytoplasm, and these enzymes have been called ‘ectoenzymes’ [ 1,2]. The biological function of an ectoenzyme can thus be explored by treatment of intact cells with impermeant reagents which inactivate the enzyme. Determination of the time course of return of the catalytic activity to steady state after irreversible inhibition has considerable potential for providing information on the biosynthesis and turnover of these specific plasma membrane proteins [3]. However, the lack of suitable irreversible inhibitors has limited the use of these methods for the study of plasma membrane proteins. dase. The enzyme is not reactivated by subsequent reaction with sodium borohydride. The periodate treatment has no effect on 2 other glycoprotein ectoenzymes, 5’-nucleotidase and alkaline phosphodiesterase I, or on alkaline phosphatase, leucine-fl-napthylamidase, and N-acetyl-fl-glucosaminidase.