AJP - Renal Physiology, Vol 254, Issue 2 191-F195, Copyright © 1988 by American Physiological Society
An ATP-inhibited soluble 5'-nucleotidase of rat kidney
M. Le Hir and U. C. Dubach
Medizinische-Universitaetspoliklinik, Kantonspital, Basel, Switzerland.
Hydrolysis of 5'-AMP by 5'-nucleotidase is a possible source of adenosine
in the kidney. A renal membrane-bound ecto-5'-nucleotidase has been
previously described. The present study deals with the catalytic properties
of a 5'-AMP phosphohydrolase partially purified from high-speed
supernatants of rat kidney homogenates. It exhibits phosphatase activity
toward 5'-AMP, 5'-IMP, and 5'-GMP, but not toward 2'- and 3'-AMP and
corresponds therefore to a 5'-nucleotidase. The hydrolysis of 5'-AMP by the
soluble 5'-nucleotidase requires divalent cations. Maximal activity is
reached with 10 microM of either Mn2+ or Co2+, whereas half-maximal
activity is obtained with approximately 400 microM Mg2+. The soluble
5'-nucleotidase exhibits Michaelis-Menten kinetics with a Km of 9.5 microM
for 5'-AMP. In the presence of 1 mM of free Mg2+, physiological
concentrations of ATP provoke an increase of the Km for 5'-AMP and a
decrease of Vmax. An increase of the pH of 0.4 units in the pH range
6.4-7.4 roughly doubles the rate of hydrolysis of 5'-AMP. The effects of
ATP and of the pH are compatible with a role of the renal soluble
5'-nucleotidase in the hydrolysis of 5'-AMP and in the production of
adenosine during hypoxia.
