2014 Volume 88 Issue 9 Pages 462-468
Because of the physiological importance of D-serine, the synthesis and degradation of D-serine have attracted interest. In mammals, D-serine is synthesized from L-serine by a eukaryotic serine racemase (SR), a member of the fold-type II group of pyridoxal 5'-phosphate (PLP)-dependent enzymes. SR structurally differs from the bacterial amino acid racemases belonging to the fold-type III PLP enzymes. In addition to racemization, SR catalyzes the serine dehydration to yield pyruvate and ammonia with the rate being comparable to that of the senile racemization. In mammals, D-serine is degraded to hydroxypyruvate and ammonia by a flavin-dependent D-amino acid oxidase. Except for mammals, D-serine dehydratase (Dsd), a fold-type III PLP enzyme, is probably responsible for the D-serine degradation. Dsds are widely distributed in various eukaryotic organisms except for mammals such as yeasts, molds, fishes, reptiles, and birds as well as in various bacterial species. The Dsd reaction depends on Zn^<2+> in addition to PLP, which is the characteristic feature of Dsd. We here introduce the enzymatic properties of SR and Dsd, and show our recent findings about their reaction mechanisms.
