Dorsett D, Jacobson K B
Biochemistry. 1982 Mar 16;21(6):1238-43. doi: 10.1021/bi00535a020.
Pteridine biosynthesis has been examined in extracts of the heads of Drosophila melanogaster by measuring the conversion of dihydroneopterin triphosphate to sepiapterin and the "drosopterins" (six eye pigments that are dipterin derivatives). These two products share a common first step in the production of an intermediate that is a branch point from which both products are formed. This first step can be catalyzed by sepiapterin synthase or by an enzyme found in particles that sediment at 600g. A substance named "quench spot" was found earlier to be at low levels in the purple mutants that were defective in drosopterin synthesis and to be restored to normal when a suppressor mutant, su(s)2, restored drosopterins in purple to normal levels. The sepia mutant is also deficient in the levels of both quench spot and drosopterins. In this report we propose that quench spot is a precursor of drosopterins, but not sepiapterin, and that it is formed from the sepiapterin synthase intermediate mentioned above. An additional precursor that is formed independently of the sepiapterin synthase pathway is also proposed that would react with quench spot to form drosopterins. These proposals are based on the following: (1) quench spot biosynthesis is observed in extracts of Drosophila heads in which [U-14C]dihydroneopterin triphosphate is the substrate; (2) Mg2+ is required for the synthesis of quench spot but either NADH or NADPH causes diminished incorporation of the label; (3) extracts from heads of a purple mutant (prbwcn) contain only 30% of the quench spot biosynthetic activity as compared to heads from wild type (Oregon-R); (4) quench spot has been purified from heads of wild-type Drosophila; (5) addition of quench spot stimulates the biosynthesis of drosopterins in an enzyme preparation from Oregon-R.
通过测量三磷酸二氢新蝶呤向蝶啶和“果蝇蝶呤”（六种眼色素，为二氢蝶啶衍生物）的转化，对黑腹果蝇头部提取物中的蝶呤生物合成进行了研究。这两种产物在生成一种中间体的过程中共享一个共同的第一步，该中间体是一个分支点，两种产物均由此形成。这第一步可由蝶啶合酶或在600g离心沉淀的颗粒中发现的一种酶催化。早些时候发现一种名为“淬灭斑”的物质在果蝇蝶呤合成有缺陷的紫色突变体中含量较低，当一个抑制突变体su(s)2将紫色突变体中的果蝇蝶呤恢复到正常水平时，该物质也恢复到正常水平。乌贼墨突变体在淬灭斑和果蝇蝶呤的水平上也都缺乏。在本报告中，我们提出淬灭斑是果蝇蝶呤而非蝶啶的前体，并且它是由上述蝶啶合酶中间体形成的。还提出了一种独立于蝶啶合酶途径形成的额外前体，它将与淬灭斑反应形成果蝇蝶呤。这些提议基于以下几点：(1) 在以[U-14C]三磷酸二氢新蝶呤为底物的果蝇头部提取物中观察到淬灭斑的生物合成；(2) 淬灭斑的合成需要Mg2+，但NADH或NADPH会导致标记物掺入减少；(3) 紫色突变体(prbwcn)头部的提取物与野生型（俄勒冈-R）头部相比，仅含有30%的淬灭斑生物合成活性；(4) 淬灭斑已从野生型果蝇头部纯化；(5) 添加淬灭斑可刺激来自俄勒冈-R的酶制剂中果蝇蝶呤的生物合成。
