Affinity purification of 5-methylthioadenosine kinase and 5-methylthioribose/ S-adenosylhomocysteine nucleosidase from Klebsiella pneumoniae

Two enzymes in the methionine salvage pathway, 5-methylthioribose kinase (MTR kinase) and 5′-methylthioadenosine/ S-adenosylhomocysteine nucleosidase (MTA/SAH nucleosidase) were purified from Klebsiella pneumoniae. Chromatography using a novel 5′-(p-aminophenyl)thioadenosine/5-(p-aminophenyl)thioribose affinity matrix allowed the binding and selective elution of each of the enzymes in pure form. The molecular mass, substrate kinetics and N-terminal amino acid sequences were characterized for each of the enzymes. Purified MTR kinase exhibits an apparent molecular mass of 46-50 kDa by SDS/PAGE and S200HR chromatography, and has a K_m for MTR of 12.2 μM. Homogeneous MTA/SAH nucleosidase displays a molecular mass of 26.5 kDa by SDS/PAGE, and a K_m for MTA of 8.7 μM. Comparisons of the N-terminal sequences obtained for each of the enzymes with protein-sequence databases failed to reveal any significant sequence similarities to known proteins. However, the amino acid sequence obtained for the nucleosidase did share a high degree of sequence similarity with the putative translation product of an open reading frame in Escherichia coli, thus providing a tentative identification of this gene as encoding an MTA/SAH nucleosidase.