A soluble 5′-nucleotidase in rat kidney. Stimulation by decavanadate

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Abstract
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 greater than 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-Km’ 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.