Substrate specificities of adenosine deaminase and adenosine phosphorylase from Bacillus cereus

The substrate specificity of two adenosine metabolizing enzymes from Bacillus cereus has been investigated, using partially purified preparations. Adenosine deaminase is shown to be highly specific for adenosine (Km = 5.6 X 10(-5) M at pH 8.1); 2'-deoxyadenosine, formycin A and 2-amino-adenosine are deaminated by the enzyme preparation, but reaction rates are at least 20 times lower than that for adenosine at concentrations up to 0.1 mM, due to higher Km and/or lower Vmax values. 3'-deoxyadenosine is not attacked. Adenosine phosphorylase, on the other hand, can readily act on adenosine, 2'-deoxyadenosine, 2-amino-adenosine and N6-monoalkyl-adenosines; again, 3'-deoxyadenosine shows no appreciable activity as a substrate. The results obtained are briefly discussed, in relation also to current investigations on purine metabolism in vegetative forms and spores of B. cereus.