Partial purification and properties of rat-heart adenosine kinase

The activity of myocardial adenosine kinase (E.N. 2.7.1.20) in a number of species was assayed. Rat heart contained the highest specific activity. From this source adenosine kinase was purified in a simple way 80-fold, until it was free of adenosine deaminase activity. A molecular weight of about 39 000 was measured. NSC 113939 (1), NSC 113940 and 8-azaadenosine inhibited myocardial adenosine kinase. Dipyridamole stimulated the enzyme at high adenosine levels, and inhibited at low substrate concentrations. A number of divalent cations could (partially) substitute for Mg2+. The optimal concentration of MgCl2 or MnCl2 was about 0.5 mM; concentrations exceeding 1 mM inhibited severely. An apparent Km for ATP of 0.1 mM was measured, whereas an apparent Km for adenosine of 0.5 muM was was found. The latter increased to 3.3 muM, when dipyridamole was added. Replacement of ATP by GTB or ITP increased the activity, and UTP and CTP were inferior as a phosphate donor.