2-amino-4-oxo-6-acetyl-7-8-dihydro-3h-9h-pyrimidodiazepine and drosopterin

The enzyme system responsible for the conversion of 2-amino-4-oxo-6-(D-erythro-1',2',3'-trihydroxypropyl)-7,8-dihyd roptridine triphosphate (dihydroneopterin triphosphate or H2-NTP) to 2-amino-4-oxo-6-acetyl-7,8-dihydro-3H,9H-pyrimido[4,5-b]-[1,4]diazepine (pyrimidodiazepine or PDA), a precursor to the red eye pigments, he drosopterins, has been purified from the heads of Drosophila melanogaster. The PDA-synthesizing system consists of two components, a heat-stable enzyme and a heat-labile enzyme. The heat-stable enzyme can be replaced by sepiapterin synthase A, a previously purified enzyme required for the Mg2+-dependent conversion of H2-NTP to an unstable compound that appears to be 6-pyruvoyltetrahydropterin (pyruvoyl-H4-pterin). The heat-labile enzyme, purified to near-homogeneity and termed PDA synthase (Mr = 48,000), catalyzes the conversion of pyruvoyl-H4-pterin to PDA in a reaction requiring the presence of reduced glutathione. Because PDA is two electrons more reduced than pyruvoyl-H4-pterin, the reducing power required for this transformation is probably supplied by glutathione. The PDA-synthesizing system requires the presence of another thiol-containing compound such as 2-mercaptoethanol when incubation conditions 2-mercaptoethanol is no longer required. Evidence is presented to indicate that the Drosophila eye color mutant, sepia, is missing PDA synthase.

Topics: Alcohol Oxidoreductases; Animals; Azepines; Chromatography, Gel; Chromatography, Ion Exchange; Drosophila melanogaster; Eye Color; Ketone Oxidoreductases; Mutation; Neopterin; Phosphorus-Oxygen Lyases; Pteridines; Pterins; Spectrophotometry

The compound 2-amino-4-oxo-6-acetyl-7,8-dihydro-3H,9H-pyrimido[4,5-b]-[1,4]diazepine (pyrimidodiazepine or PDA, for short) is a precursor of the red eye pigments called the drosopterins in Drosophila melanogaster. The precursor of PDA is 2-amino-4-oxo-6-(D-erythro-1',2',3'-trihydroxypropyl)-7,8-dihydrop teridine triphosphate (dihydroneopterin triphosphate or H2-NTP). The synthesis of of PDA from H2-NTP requires reduced glutathione, another thiol such as 2-mercaptoethanol, Mg2+, and at least three enzymes: one that is missing in the eye color mutant, sepia; one that is present only in limited quantities in the mutant, clot; and a third one that has been described as sepiapterin synthase A. The last enzyme is present only in relatively small quantities in the mutant, purple. Because PDA is two electrons more reduced than H2-NTP, it would appear that the reducing power needed for this transformation is probably supplied by glutathione. Oxidized glutathione cannot replace reduced glutathione in the system. The yield of PDA produced enzymatically from H2-NTP can be as high as 40% under optimal conditions.

Topics: Animals; Azepines; Chromatography, High Pressure Liquid; Drosophila melanogaster; Glutathione; Kinetics; Magnesium; Magnesium Chloride; Mercaptoethanol; Neopterin; Pteridines; Pterins

The structure of an intermediate, in drosopterin biosynthesis, as 6-acetylpyrimidodiazepine has been confirmed by high-resolution mass spectra, 13C NMR, chemical ionization mass spectra, and chemical properties. A trivial name of 6-acetylhomopterin is suggested and should replace the term "quench spot" used heretofore. The structure of drosopterin includes, in part, a pyrimidodiazepine, a compound that consists of a fused six- and seven-membered heterocyclic ring system. Earlier studies demonstrated that 6-acetylhomopterin strongly stimulated the enzymatic synthesis of drosopterin and related eye pigments by preparations from Drosophila. The occurrence in nature is quite limited for diazepines; drosopterin and homopterin are the first examples in eukaryotes.

Topics: Animals; Azepines; Chemical Phenomena; Chemistry; Chromatography, High Pressure Liquid; Drosophila; Magnetic Resonance Spectroscopy; Mass Spectrometry; Models, Structural; Pteridines; Pterins

A compound that is involved in the biosynthesis of the drosopterin eye pigments has been isolated from the heads of Drosophila melanogaster. Analyses of this compound by chemical, mass spectral, and proton nuclear magnetic resonance techniques in conjunction with biochemical considerations provide evidence for the structure 2-amino-4-oxo-6-acetyl-7,8-dihydro-3H,9H-pyrimido[4,5-b][1,4]diazepine (PDA). At least three eye pigments (drosopterin, isodrosopterin, and aurodrosopterin) are synthesized when PDA and 2-amino-4-oxo-(D-erythro-1',2',3'-trihydroxypropyl)-7.8-dihydropteridine triphosphate (dihydroneopterin triphosphate) are incubated with Mg2+ and protein fractions prepared from Drosophila heads. The synthesis of aurodrosopterin, in addition, requires reduced pyridine nucleotide. Other evidence suggests that dihydroneopterin triphosphate is a biosynthetic precursor of PDA.

Topics: Animals; Azepines; Drosophila melanogaster; Mass Spectrometry; Pteridines; Pterins; Retinal Pigments; Spectrophotometry