In vitro regulation of rat heart 5'-nucleotidase by adenine nucleotides and magnesium.

Adenosine diphosphate was found to be a powerful competitive inhibitor of 5’nucleotidase partially purified from rat heart, with a greater apparent affinity for the enzyme than ATP. The inhibition imposed by either nucleotide was not relieved by a number of metabolic intermediates known to accumulate in the hypoxic heart. The enzyme required divalent cations for activity. Magnesium relieved the nucleotide-induced inhibition completely. This relief was in part caused by the formation of nucleotide-magnesium complexes which were less inhibitory. Further increases in magnesium could relieve the inhibition imposed by the complexes. It is proposed that the regulation of this enzyme in vivo may depend on the deinhibition by magnesium.