AJP - Endocrinology and Metabolism, Vol 256, Issue 3 E386-E391, Copyright © 1989 by American Physiological Society
AMP and IMP dephosphorylation by soluble high- and low-Km 5'-nucleotidases
J. Spychala, V. Madrid-Marina, P. J. Nowak and I. H. Fox
Department of Internal Medicine, Clinical Research Center, University Hospital, Ann Arbor, Michigan 48101-0108.
Three distinct 5'-phosphomonoesterase activities were isolated from soluble
fractions of human placenta, cultured human T and B lymphoblasts, and rat
liver using 5'-AMP-sepharose 4B affinity chromatography. We define these
activities as "low-Km" 5'-nucleotidase, "high-Km" 5'-nucleotidase, and
nonspecific phosphatase. High-Km 5'-nucleotidase was eluted with 0.5 M
NaCl, low-Km 5'-nucleotidase was eluted with 10 mM ADP, and nonspecific
phosphatase was not retained on the column. We have found significant
variability in the relative content of high- to low-Km activities in the
tissues studied with the ratios ranging from 5.5 to 264. The properties
were studied after further purification. The molecular mass of the low-Km
enzymes ranged from 72.5 to 209 kDa, optimum pH ranged from 7.4 to 9.0, Km
for AMP ranged from 7 to 15 microM, and Km for IMP ranged from 10 to 26
microM. The molecular mass of the high-Km enzymes ranged from 182 to 210
kDa, pH optimum was at 6.5, Km for AMP ranged from 3.0 to 9.4 mM, and the
Km for IMP ranged from 0.3 to 0.5 mM. The data indicate that the soluble
low- and high-Km 5'-nucleotidase coexist in the mammalian cells and tissues
studied. These observations suggest a complex system for the regulation of
nucleoside 5'-monophosphate dephosphorylation.
