METABOLISM IN HUMAN-CELLS OF THE D-ENANTIOMER AND L-ENANTIOMER OF THECARBOCYCLIC ANALOG OF 2'-DEOXYGUANOSINE - SUBSTRATE ACTIVITY WITH DEOXYCYTIDINE KINASE, MITOCHONDRIAL DEOXYGUANOSINE KINASE, AND 5'-NUCLEOTIDASE

The carbocyclic analog of 2'-deoxyguanosine (CdG) has broad-spectrum a ntiviral activity. Because of recent observations with other nucleosid e analogs that biological activity may be associated the L enantiomer rather than, as expected, with the D enantiomer, we have studied the m etabolism of both enantiomers of CdG to identify the enzymes responsib le for the phosphorylation of CdG in noninfected and virally infected human and duck cells. We have examined the enantiomers as substrates f or each of the cellular enzymes known to catalyze phosphorylation of d eoxyguanosine, Both enantiomers of Cde were substrates for deoxycytidi ne kinase (EC 2.7.1.74) from MOLT-4 cells, 5'-nucleotidase (EC 3.1.3.5 ) from HEp-2 cells, and mitochondrial deoxyguanosine kinase (EC 2.7.1. 113) from human platelets and CEM cells. For both deoxycytidine kinase and mitochondrial deoxyguanosine kinase, the L enantiomer was the bet ter substrate. Even though the D enantiomer was the preferred substrat e with 5'-nucleotidase, the rate of phosphorylation of the L enantiome r was substantial. The phosphorylation of D-CdG in MRC-5 cells was gre atly stimulated by infection with human cytomegalovirus. The fact that the phosphorylation of D-CdG was stimulated by mycophenolic acid and was not affected by deoxycytidine suggested that 5'-nucleotidase was t he enzyme primarily responsible for its metabolism in virally infected cells. D-CdG was extensively phosphorylated in duck hepatocytes, and its phosphorylation was not affected by infection with duck hepatitis B virus. These results are of importance in understanding the mode of action of D-CdG and related analogs and in the design of new biologica lly active analogs.