Some properties of adenosine kinase from Ehrlich ascites-tumour cells

Publisher Website
Google Scholar
Abstract
Adenosine kinase was measured in dialysed extracts from Ehriich ascites-tumor cells by a chromatographic procedure. In the absence of added Mg2+ the Km values for ATP and adenosine were 0.22 mM and 2.8 [mu]M respectively. The maximum velocity ofadenosinekinasewithfreeATP was about 3 times that with the Mg2+-ATP complex. Free Mg2+ was a non-competitive inhibitor of the reaction. A small amount of added Mg2+, Mn2+ or Ca2+ was required for maximum adenosine kinase activity after cation bound to the enzyme was released by treatment with p-chloromercuri-benzoate and then removal by dialysis. GTP, ITP, deoxy-ATP, deoxy-GTP, CTP, xanthosine triphosphate, UTP and thymidine triphosphate could partially or completely replace ATP as a phosphate donor. The reaction of ATP with adenosine kinase was competitively inhibited by AMP, GMP, IMP, ADP, deoxy-ADP and IDP (Ki 0.2, 1.1, 5.9, 1.2, 0.5 and 0.78 mM respectively). Enzymic activity was markedly affected by the relative concentrations of AMP, ADP and ATP in assay mixtures. The results are discussed in terms of possible mechanisms regulating the rate of adenosine kinase in vivo.