PLP catabolism: Identification of the 4-pyridoxic acid dehydrogenase gene in Mesorhizobium loti MAFF303099

The function of the mlr6793 gene from Mesorhizobium loti MAFF303099 has been identified. This gene encodes 4-pyridoxic acid dehydrogenase, an enzyme involved in the catabolism of PLP (Vitamin B6). This enzyme was overexpressed in Escherichia coli and characterized. 4-Pyridoxic acid dehydrogenase is a 33 kDa protein that catalyzes the four electron oxidation of 4-pyridoxic acid to 3-hydroxy-2-methylpyridine-4,5-dicarboxylate, using nicotinamide adenine dinucleotide as a cofactor. The kcat for NADH production is 0.01 s−1. The KM values for 4-pyridoxic acid and NAD are 5.8 and 6.6 μM, respectively.