Studies on the clinical applications of the determinations of serum leucine

aminopeptidase (LAP) activities using leucinamide as the substrates

Abstract

Serum leucine aminopeptidase (LAP) activities were determined in normal and in various kinds of diseases by means of Okuda-Fujii's method, which consisted in measurement of ammonia liberated by the action of LAP with direct colorimetric determination of ammonia, and were compared with those determined by the method in which leucyl-β-naphthylamide as used as the substrate to clarify the clinical meaning of the elevation of LAP activities determined by the both methods. LAP activity determined by the former method (LAP-NH₃) was significantly higher than those determined by the latter method (LAP-Nap) in hepatocellular damages such as acute hepatitis, and LAP activity determined by the latter method showed the tendency to be higher than those determined by the former in obstructive jaudice.
It was demonstrated that the serum of normal rats and CCl₄ treated rats contained several multi-forms of the enzymes (LAP-I and LAP-II) which showed different substrate specificities toward leucinamide and leucine-β-naphthylamide by the TEAE cellulose column chromatography.
In normal rat, LAP-I activity was higher in the NH₃-method, and LAP-II activity was higher in the Nap-method. Marked increase of LAP activity in CCl₄ treated rats was considered to be caused by the marked increase of LAP-NH₃ belonging to LAP-I, and slight increases of LAP-NH₃ and LAP-Nap belonging to LAP-II.