Metabolism of 4- N -Hydroxy-Cytidine in Escherichia coli

Abstract

4- N -hydroxy-cytidine was found to substitute for uridine as a pyrimidine supplement for the growth of Escherichia coli Bu − . Measurement of the incorporation of 4- N -hydroxy-cytidine- 2 - 14 C into ribonucleic acid and deoxyribonucleic acid revealed that this compound was converted to cytidine or uridine before utilization. Two pathways for metabolism were considered: (i) the reduction of 4- N -hydroxy-cytidine to cytidine followed by deamination, (ii) the direct hydrolysis of hydroxylamine from 4- N -hydroxy-cytidine to yield uridine. A threefold increase in cytidine (deoxycytidine) deaminase (EC 3.5.4.5) activity, when the cells were grown on 4- N -hydroxy-cytidine, suggested the involvement of this enzyme. More direct proof was obtained by purifying the deaminase 185-fold and finding that it released hydroxylamine from 4- N -hydroxy-cytidine at one-fiftieth the rate at which ammonia was removed from cytidine. This result is consistent with the slower rate of growth of the Bu − cells on 4- N -hydroxy-cytidine than cytidine and suggests that the second pathway is the major route for utilization of this compound.