Clinical Chemistry 1985-10-01

Use of L-leucyl-3-carboxy-4-hydroxyanilide as substrate for determining the activity of microsomal aminopeptidase in serum.

M Shimamoto, S Takewaki, S Sakuraoka, T Nagasawa, K Kuroiwa, O Kodama, T Akatsuka

Index: Clin. Chem. 31 , 1636-1639, (1985)

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Abstract

We describe a colorimetric method for assay of microsomal aminopeptidase (EC 3.4.11.2) activity in serum. We use a new substrate, L-leucyl-3-carboxy-4-hydroxyanilide, p-xylenol as coupler, and sodium metaperiodate as oxidizing reagent. The colored substance formed by the oxidative condensation between p-xylenol and 5-aminosalicylic acid absorbs maximally at 635 nm, and can be directly measured in serum. In a previous method for this enzyme, L-leucyl-beta-naphthylamide was used as substrate and beta-naphthylamine, a carcinogenic reagent used as a standard in making the assay, was unsuitable for routine use. We found a close correlation between results obtained with the new, safer method and with the previous method.