Purification, kinetics, and repression control of bacterial trans-N-deoxyribosylase.

Trans-N-deoxyribosylase,i the enzyme that catalyzes deoxyribosyl transfer from deoxyribonucleosides to free purines and pyrimidines, was first demonstrated by MacNutt in Lactobacillus helveticus (1). It was subsequently found in other lactobacilli and related organisms that require deoxyribonucleosides for growth (2, 4). The nature of the reaction and the nonparticipation of phosphate were established by Kalckar, MacNutt, and Hoff-Jergensen (9), and partial purifications from extracts of Lactobacillus helveticus (2)) Lactobacillus leichmannii (4)) Thermobacter acidophilus (lo), and Lactobacillus delbrueckii (3) have been reported. The present investigation was begun in connection with our studies of the role of vitamin B1t in deoxyribonucleotide synthesis (6, 7). an attempt was made to assess the function of trans.Ndeoxyribosylase in the metabolism of lactobacilli, and the results of this inquiry are reported herein. The data also revealed that enzyme levels vary with changes in the size or composition of the acid-soluble deoxyribosyl pool, and it is concluded that tram-A-deoxyribosylase is repressed by one or more of the compounds in this ~001.~ Finally, evidence is presented of certain interesting features of the kinetics of highly purified enzyme from Lactobacillus leichmannii (ATCC 7830). It was observed in incubations initially containing the two substrates, thymidine and adenine, that notable inhibition occurs at high adenine concentrations. Preliminary studies suggest that adenine competes for a thymidine site.