Some properties of glycine aminotransferase purified from Rhodopseudomonas palustris No. 7 concerning extracellular porphyrin production

Glycine aminotransferase (EC 2.6.1.4; GlyAT) was presumed to be an enzyme concerning the supply of glycine for the extracellular porphyrin production by Rhodopseudomonas palustris No. 7. GlyAT was purified from strain No. 7 as an electrophoretically homogenous protein. The enzyme was a monomer protein with the molecular weight of about 42,000. From the absorption spectrum of the enzyme (350 nm, 410 nm), it was indicated that the enzyme had pyridoxal phosphate as a prosthetic group. The enzyme showed high substrate specificity for glutamate as an amino group donor. Apparent Kms for glutamate and glyoxylate were 6.20 mM and 3.75 mM, respectively. The Vmax and Kcat for glutamate were 66.8 mumol/min/mg protein and 46.8 s-1, respectively. The Vmax and Kcat for glyoxylate were 68.8 mumol/min/mg protein and 48.2 s-1. The optimum temperature and pH were 40-45 degrees C and 7.0-7.5, respectively. The enzyme activity lowered to about 50% in the presence of 15 mM ammonium chloride.