BIOPTERIN .6. PURIFICATION AND PRIMARY AMINO-ACID SEQUENCE OF MAMMALIAN D-ERYTHRO-7,8-DIHYDRONEOPTERIN TRIPHOSPHATE SYNTHETASE

An enzyme that catalyzes the conversion of 2-amino-6(-5′-triphosphoribosyl)amino-5- or 6-formamido-6-hydroxypyrimidine, but not of guanosine triphosphate, to quinonoid 6-(d-erythro-1′-2′-3′-trihydroxypropyl)dihydropterin triphosphate and formic acid has been purified to homogeneity from some mammalian brain and liver. The enzyme of a single strand is a basic protein of 9177 daltons consisting of 68 amino acid residues-except the enzyme from rat brain, which has one additional aspartic acid as residue 7. The enzyme possesses three free SH groups and, in its most active form, 1 mol of phosphate per mole of enzyme. Peptides isolated after hydrolysis with trypsin, chymotrypsin, or weak acid were separated by thin-layer chromatography and sequenced manually by Edman degradation. The complete sequence of the molecule was established as follows: {Mathematical expression} © 1979 Plenum Publishing Corporation.