KINETICS OF ADENYLATE METABOLISM IN HUMAN AND RAT MYOCARDIUM

Pathways producing and converting adenosine have hardly been investiga ted in human heart, contrasting work in other species. We compared the kinetics of enzymes associated with purine degradation and salvage in human and rat heart cytoplasm assaying for adenosine deaminase, nucle oside phosphorylase, xanthine oxidoreductase, AMP deaminase, AMP- and IMP-specific 5'-nucleotidases, adenosine kinase and hypoxanthine guani ne phosphoribosyltransferase (HGPRT), Xanthine oxidoreductase was not detectable in human heart. The K-m-values of the AMP-catabolizing enzy mes were 2-5 times higher in human heart; the substrate affinity of:th e other enzymes was in the same order of magnitude in both species. Th e maximal activity (V-max) of adenosine kinase was the same in both sp ecies, but KGPRT in man was only 12% of that in the rat. For human hea rt the V-max-values of adenosine deaminase, nucleoside phosphorylase, AMP- and IMP-specific 5'-nucleotidases, and AMP deaminase were 25-50% of those for rat heart, We conclude that human heart is less geared to purine catabolism than rat heart as is evident from the lower activit ies of the catabolic enzymes. Maintenance of the nucleotide pool may t hus play a more important role in human heart.