This review summarizes functions, regulations, and structures of NAD(P)^+ and vitamin B_6 (B_6) enzymes which were found by us. NADP^+-dependent meso-diaminopimelate dehydrogenase, a kind of D-amino acid dehydrogenase, functions in lysine biosynthesis of Bacillus sphaericus. Properties of the enzymes purified from B. sphaericus, Corynebacterium glutamicum, Brevibacterium sp. were compared. The amino acid residues of the active site in the B. sphaericus enzyme were identified by the site-directed mutagenesis. NAD^+-dependent lysine dehydrogenase of Agrobacterium tumefaciens functions in degradation of L-lysine. Stereochemistry of the enzyme reaction, allosteric properties of the enzyme, a lysine residue in the effector-binding site, and a cysteine residue essential for its activation were characterized. The properties and primary structures of NADP^+-dependent dehydrogenases acting on the hydroxylgroup of amino acids, D-threonine dehydrogenase, D-phenylserine dehydrogenase, and serine dehydrogenase, were studied. Moreover, D-threonine dehydrogenase homologues, YhaE and YbbQ of Escherichia coli and serine dehydrogenase homologues of E. coli (YdfG) and Saccharomyces cerevisiae (Ymr226cp) were characterized. Inducible two kinds of B_6 enzymes, phenylserine dehydratase and phenylserine aldolase, and a homologue of the aldolase, GLY1 protein of S. cerevisiae, were characterized. The aldolase gene was present in an operon with a regulatory protein gene. Function of the reguratory protein was also described.