A SOLUBLE 5'-NUCLEOTIDASE IN RAT-KIDNEY - STIMULATION BY DECAVANADATE

A soluble 5'-nucleotidase was identified in rat kidney and partially purified. Compared with 5'-IMP, 5'-AMP was a poor substrate. The affinity for 5'-IMP was very low (S0.5 > 1 mM) in the absence of an activator, and it was much increased (S0.5 = 0.1 mM) by 2,3-bisphosphoglycerate (2,3-DPG). ATP and bisadenosyl tetraphosphate were further activators. The pH optimum was 6.3. Those properties suggest that the renal soluble 5'-nucleotidase is identical with the 'high-K(m)' 5'-nucleotidase purified previously from liver, heart and erythrocytes. Decavanadate (100 nM) increased the rate of hydrolysis of 1 mM-5'-IMP 16-fold. The effect was specific for the decameric form of vanadate, since it was not reproduced by either decavanadate-free orthovanadate or pervanadate. Half-maximal activation was obtained at 1.4 nM-decavanadate. Decavanadate increased the affinity of the soluble 5'-nucleotidase for 5'-IMP. The effects of 2,3-DPG and of vanadate were not additive. Thus decavanadate probably influences the soluble 5'-nucleotidase in the same way as 2,3-DPG, but with a much higher potency.