The enzymology of N-deoxyribosyltransferase from Lactobacillus leichmannii
Nucleoside deoxyribosyltransferase catalyses the transfer of a2- I deoxyribose sugar between purine and pyrimidine bases. In nature, their occurence appears to be confined to selected lactic acid bacteria, notably those from the genus Lactobacillus. L. leichmannii possess two distinct nucleoside deoxyribosyltransf erases: N-deoxyribosyltransf erase -I, which mediates the transfer of the glycosyl group between purine bases exclusively, and N-deoxyribosyltransferase-11 which catalyses the transfer of the 2-deoxyribose sugar to and from purine and pyrimidine bases. These enzymes are capable of accepting a wide number of heterocyclic base analogues as substrates and the necessary structural requirements for a competent acceptor have been defined. Similarly, it has been established that the Ndeoxyribosyltran sf erase enzymes possess relatively little tolerance towards substrates with modified sugar moieties. The transfer reaction proceeds via an enzyme -substitution or ping-pong . bi-bi mechanism and kinetic and radiolabelling experiments provide reasonable support for the existence of a covalent glycosyl intermediate. Chemical modification of Ndeoxyribosyltransferase-11 with specific chemical reagents suggest that a histidine and, or carboxyl residues may participate in binding and catalysis at the active site of the enzyme.