Intermediates in the conversion of 5'-S-methylthioadenosine to methionine in Klebsiella pneumoniae

Extracts of Klebsiella pneumoniae oxidatively convert 1-phospho-5-S-methylthioribose (1-PMTR) to alpha-keto-gamma-methylthiobutyrate, a precursor of methionine, and to S-methylthiopropionate and formate. One equivalent of formate is produced per equivalent of alpha-keto-gamma-methylthiobutyrate and two equivalents of formate per equivalent of methylthiopropionate. Two compounds were identified as intermediates in this reaction sequence: 1-phospho-5-S-methylthioribulose (1-PMT-ribulose) and 1-phospho-2,3-diketo-5-S-methylpentane. The enzyme, 1-PMTR isomerase, which converts 1-PMTR to 1-PMT-ribulose was highly purified. In addition, a protein fraction was isolated which converts 1-PMT-ribulose to the phosphodiketone. A second protein fraction was isolated that converts the phosphodiketone to an intermediate which has not been isolated so far. This intermediate is oxidatively converted to alpha-keto-gamma-methylthiobutyrate and S-methylthiopropionate by a third protein fraction. Methylthiopropionate is not derived from free alpha-keto-gamma-methylthiobutyrate.