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PubMed1983

Human placental deoxyadenosine and deoxyguanosine phosphorylating activity.

We studied deoxyadenosine and deoxyguanosine phosphorylating activities in human placental cytosol. The specific activities of nucleoside kinase enzymes in nanomoles per h per mg +/- SD were as follows: adenosine kinase, 30 +/- 14; deoxyadenosine kinase, 12 +/- 2; deoxycytidine kinase, 0.30 +/- 0.04; and deoxyguanosine kinase, 27 +/- 16. Three major activities were resolved by ion exchange and affinity chromatography: deoxyguanosine-deoxycytidine kinase, deoxycytidine-deoxyadenosine kinase, and adenosine-deoxyadenosine kinase. Two other activities contained significant quantities of deoxyadenosine kinase. Deoxyguanosine-phosphorylating activity eluted as a single peak in association with deoxycytidine kinase. This deoxyguanosine-deoxycytidine kinase had an apparent molecular weight of 54,000, a Stokes radius of 31 A, and apparent Km values of 10, 130, and 14 microM for deoxyguanosine, deoxycytidine, and ATP, respectively. Four peaks of deoxyadenosine phosphorylating activity were resolved by affinity chromatography with AMP-Sepharose 4B. Adenosine-deoxyadenosine kinase had an apparent molecular weight of 38,000, a Stokes radius of 27.4 A, and apparent Km values of 0.4, 510, and 75 microM for adenosine, deoxyadenosine, and ATP, respectively. Attempts to distinguish whether adenosine-deoxyadenosine kinase was one enzyme with these two activities or two separate enzymes suggested that the former was the case. Deoxycytidine-deoxyadenosine kinase had apparent Km values of 0.7, 670, and 12 microM for deoxycytidine, deoxyadenosine, and ATP, respectively. Its apparent molecular weight was estimated to be 49,000 and its Stokes radius 30 A. Two other minor peaks of deoxyadenosine-phosphorylating activity had characteristics different from either deoxycytidine kinase or adenosine kinase-associated deoxyadenosine kinase. Our studies indicate that human placental cytosol contains a complex mixture of nucleoside kinase enzymes.

Cells, Cultured↗
PubMed1992

Factors influencing the inhibition of repair of irradiation-induced DNA damage by 2'-deoxycoformycin and deoxyadenosine.

Permeabilized L5178Y cells were used to investigate the mechanism underlying inhibition of the repair of irradiation-induced DNA strand breaks by 2'-deoxycoformycin combined with deoxyadenosine. Permeabilized cells repaired DNA strand breaks as effectively as did intact cells, and at deoxyadenosine concentrations that produced similar levels of deoxyadenosine triphosphate (dATP), repair of DNA strand breaks was inhibited by 2'-deoxycoformycin plus deoxyadenosine to a comparable extent in both types of cells. Accompanying the increase in intracellular dATP produced by 2'-deoxycoformycin combined with deoxyadenosine was a fall in levels of deoxythymidine triphosphate (dTTP), deoxyguanosine triphosphate (dGTP), and deoxycytidine triphosphate (dCTP). The addition of dTTP, dGTP, and dCTP reversed the inhibition of DNA repair by 2'-deoxycoformycin plus deoxyadenosine, although the level of dATP was not affected. Reducing the phosphorylation of deoxy-adenosine to dATP by the addition of adenosine prevented the decrease in levels of dTTP, dGTP, and dCTP and the inhibition of DNA repair by 2'-deoxycoformycin and deoxyadenosine. In contrast, increasing the intracellular levels of dATP by the addition of 2'-deoxycoformycin together with dATP, deoxyadenosine diphosphate (dADP), or deoxyadenosine monophosphate (dAMP) had no effect on the levels of the other deoxynucleotide triphosphates and did not inhibit DNA repair. Moreover, DNA repair was not inhibited by the breakdown products of deoxyadenosine, adenine, or deoxyribose. These results suggest that inhibition of the repair of irradiation-induced DNA strand breaks by 2'-deoxycoformycin combined with deoxyadenosine requires the phosphorylation of deoxyadenosine and involves alterations in the levels of deoxynucleotide triphosphates.

Adenosine↗