Genetical and biochemical studies on human phosphoserine phosphatase

1. Phosphoserine phosphatase (PSP), specific for D- and L-phosphoserine, has been identified in all human tissues. 2. PSP shows no activity towards phosphorylated serine residues in phosphoproteins. 3. In most tissues, PSP consists of a single major isozyme, probably determined by a single autosomal locus. 4. Other isozymes, identified quite frequently in such post-mortem tissues as kidney and liver, appear to be due to post-translational modification, the mode of which has not yet been identified. 5. Two different rare electrophoretic variants have been identified in 1% and 0.25% of 378 post-mortem kidneys (PSP 2-1 and PSP 3-1 respectively). 6. The three banded isozyme pattern of the rare variants suggests PSP is a dimeric enzyme. From gel filtration results the subunit molecular size is 26 000 daltons. 7. Homologous PSP isozymes have been detected in primates with similar electrophoretic mobility to that of the human enzyme.