PURIFICATION AND CHARACTERIZATION OF 6-PYRUVOYL TETRAHYDROPTERIN SYNTHASE FROM HUMAN PITUITARY-GLAND

6-Pyruvoyl tetrahydropterin synthase, the enzyme that catalyses the co nversion of 7,8-dihydroneopterin triphosphate to 6-pyruvoyl tetrahydro pterin, was purified 3,330-fold from human pituitary gland with an ove rall recovery of 30%. The native enzyme has a molecular mass of 68 kD and consists of four identical subunits of 16.5 kD. The pH optimum of the enzyme in Tris/HCl buffer is 7.5. The enzyme is dependent on Mg2and NADPH and has a Michaelis-Menten constant of 10 muM for its natura l substrate, 7,8-dihydroneopterin triphosphate. The isoelectric point of the human enzyme is 4.3-4.6. The human pituitary gland enzyme is he at instable in contrast to the enzymes from human, rat and salmon live r, and Drosophila head. The amino acid composition showed remarkably h igh content of acidic amino acids Asp and Glu. The N-terminus was foun d to be blocked.