The metabolism of deoxyribonucleosides in Lactobacillus acidophilus: Regulation of deoxyadenosine, deoxycytidine, deoxyguanosine and deoxythymidine kinase activities by nucleotides

Abstract

1. 1. The presence of deoxycytidine kinase, as well as of deoxyadenosine, deoxyguanosine and thymidine kinase activities, is reported in Lactobacillus acidophilus. 2. 2. Phosphorylation of each deoxynucleoside is inhibited most effectively by its homoogous deoxynucleoside triphosphate. Besides inhibiting deoxycytidine kinase, dCTP also inhibits deoxyguanosine kinase activity, but stimulates deoxyadenosine and deoxythymidine phosphorylation. 3. 3. The inhibition of deoxycytidine, deoxyguanosine or deoxyadenosine phosphorylation by the corresponding triphosphate is reversed by UTP and dUTP, but not by dTTP which augmented the inhibition in certain cases. The inhibition of thymidine kinase by dTTP was readily reversed by dCTP. 4. 4. Preliminary purification of the bacterial deoxycytidine kinase is described, and its properties are compared with those of the enzyme from calf thymus. The pH curve is biphasic, with optima at pH 7.6 and 10.5. The mol. wt., as estimated by gel filtration, is only about 35 000. The enzyme is slightly activated by mercurial reagents, apparently without loss of regulatory properties. Initial kinetic experiments yielded linear double-reciprocal plots when either deoxycytidine or ATP-Mg 2− was varied. The end-product inhibitor dCTP apparently is competitive; K i dCTP, 5.0·10 −5 M.