Biopterin

Abstract

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:

$$\begin{gathered} Ile - Ser - His - Gly - P\mathop h\limits^5 e - Arg - Tyr - Asp - Ala - I\mathop l\limits^1 \mathop e\limits^0 - Ala - Lys - Leu - \hfill \\ Phe - A\mathop r\limits^1 \mathop g\limits^5 - Pro - Phe - Phe - Cys - G\mathop l\limits^2 \mathop y\limits^0 - Asp - Gly - Tyr - Gly - H\mathop i\limits^2 \mathop s\limits^5 - Arg - \hfill \\ Ile - Gly - Glu - T\mathop h\limits^3 \mathop r\limits^0 - Val - Tyr - Tyr - Ala - G\mathop l\limits^3 \mathop y\limits^5 - Ser - Leu - Lys - Tyr - \hfill \\ C\mathop y\limits^4 \mathop s\limits^0 - Ala - Arg - Ser - Phe - A\mathop s\limits^4 \mathop p\limits^5 - Val - Gly - Ala - Glu - I\mathop l\limits^5 \mathop e\limits^0 - Ile - Cys - \hfill \\ Lys - Gly - P\mathop h\limits^5 \mathop e\limits^5 - Tyr - Tyr - Phe - Gly - I\mathop l\limits^6 \mathop e\limits^0 - Tyr - Lys - Arg - Arg - V\mathop a\limits^6 \mathop l\limits^5 - \hfill \\ Ser - Glu - Val. \hfill \\ \end{gathered}$$