抄録
Vitamin B_6, consisting of natural six forms, pyridoxine, pyridoxal, pyridoxamine and their 5'-phosphate forms, functions as the essential nutrient through supporting the enzymes involved in metabolisms of amino acids and others as a coenzyme. They nutritionally show the same efficiency, because they can be interchangeable through a salvage pathway to form the coenzyme form, pyridoxal 5'-phosphate. In contrast, recent works show that the individual form has a specific function, such as anti-active carbonyl and antioxidation ones. We have found that vitamin B_6 compounds protected fission yeast cells against oxidative death more efficiently than vitamin C, and inhibited tyrosinase reaction by scavenging reactive oxygen specie(s) essential for the enzyme reaction. The genes encoding enzymes involved in the metabolism of vitamin B_6 compounds were identified, and structures and functions of the enzymes were elucidated. Pyridoxal reductase in the fission yeast cells was a new member of aldo-keto reductase superfamily, and suggested to be involved in an efflux system of pyridoxal after reducing to pyridoxine. All of genes involved in the degradation for vitamin B_6 were identified. They located on a chromosome of Mesorhizobium loti, a nitrogen-fixing symbiotic microorganism, as a cluster. The enzymes were over-expressed and characterized. E. coli cells containing the high amount of the enzymes were used for bioconversion of pyridoxine to 4-pyridoxolactone. Three of the enzymes were applied to a new individual determination method of vitamin B_6 compounds.
