Studies on the clinical application of serum leucine aminopeptidase and monoamine oxidase estimation by the direct colorimetric determination of ammonia
Ito, S.; Takaoka, T.; Kishi, S.; Okuda, H.; Fujii, S.
Tokushima Journal of Experimental Medicine 24(1 no 2): 33-40
1977
ISSN/ISBN: 0040-8875 PMID: 565088 Document Number: 117975
New methods for the determination of leucine aminopeptidase (LAP) activity using leucineamide as substrate, and of monoamine oxidase (MAO) activity using benzylamine (BZA-oxidase) and n-butylamine (NBA-oxidase) as substrates are presented. These methods are based on the direct colorimetric measurement of the amount of ammonia liberated. Serum LAP activity in acute hepatitis obtained by the NH3-method was much higher than that obtained by the leucyl-.beta.-naphthylamide (Nap)-method, but the latter method gave a higher value for serum LAP activity in obstructive jaundice. The serum of normal rats and CCl4-treated rats contained isozymes (LAP-1 and LAP-II) which showed different substrate specificities toward leucinamide and Nap. The NH3-method showed higher LAP-I and lower LAP-II activities than the Nap-method. Serum LAP-I activity elevated markedly in CCl4-treated rats by the NH3-method, but not by the Nap-method. Leucinamide is apparently more suitable as the substrate for the measurement of serum LAP. BZA-oxidase activity was higher than NBA-oxidase activity in human liver extract, but was lower than the latter in human serum. Serum MAO activity was more increased in liver cirrhosis and hepatic cancer than in acute or chronic hepatitis. Increase of serum MAO activity related closely with the grade of fibrosis determined histologically in chronic hepatitis and liver cirrhosis. n-Butylamine was more suitable as substrate than benzylamine for the determination of serum MAO activity, because NBA-oxidase activity was higher than that of BZA-oxidase in human serum.