SERINE RACEMASES FROM PROKARYOTES TO EUKARYOTES: AN OVERVIEW ON ITS ROLE AND EXISTENCE

Serine racemase is an amino-acid racemase enzyme which exhibits pyridoxal 5-phosphate dependent metabolic activities of racemases and dehydratases. It has been reported in both prokaryotes and eukaryotes. Serine racemase metabolizes D-serine from L-serine and eliminates a water molecule from both serine forms to produce ammonia and pyruvate. Enzyme folding and activity is modulated by various co-factors, transcription factors and regulatory proteins. Initial evidence of the existence of serine racemase came from insects followed by extensive data research on bacteria, plants and mammals. In prokaryotes it is involved in antibiotic resistance and adaptation. Whereas, in eukaryotes such as mammals and plants, this enzyme acts as an important neurological compound involved in synaptic plasticity and regulation of carbon and nitrogen cycles, respectively. Dependence of bacterial and mammalian serine racemases on various physiological properties suggested that L-to D-amino acid racemization is evolutionarily conserved in these organisms. Pathophysiology of serine racemases in mammals has been linked to its involvement in various neurological syndromes like Schizophrenia, Alzheimer’s, Parkinson as well as in amyotrophic lateral sclerosis. This review comprehensively highlights established notions and current status of investigative pursuits variously reported for the distribution, modulation and pathophysiology of serine racemases and D-serine.