Various vitamin B6 enzymes play important roles in mammalian and microbial metabolism of selenium amino acids. Selenocysteine is synthesized from selenohomocysteine by catalysis of cystathionine beta-synthase and cystathionine gamma-lyase, which both require pyridoxal phosphate. Selenocysteine beta-lyase, a new B6-enzyme, exclusively catalyzes beta-elimination of selenocysteine, and occurs in mammalian systems and bacteria. Methionine gamma-lyase, cysteine desulfurase, cysteine sulfinate desulfinase, and D-selenocystine alpha,beta-lyase, which are B6-enzymes, act on cysteine, cysteine sulfinate, D-cystine, and their derivatives, and their selenium counterparts indiscriminately. Their reaction mechanisms are comparatively described.