Drosophila pterins

First isolated from human urine, biopterin (Fig. 15-17) is present in liver and other tissues where it functions in a reduced form as a hydroxylation coenzyme (see Chapter 18).338 It is also present in nitric oxide synthase (Chapter 18).341/342 Other functions in oxidative reactions, in regulation of electron transport, and in photosynthesis have been proposed.343 Neopterin, found in honeybee larvae, resembles biopterin but has a D-erythro configuration in the side chain. The red eye pigments of Drosophila, called drosopterins, are complex dimeric pterins containing fused 7-membered rings (Fig. 15-17).344 345... 

Among the simple pterins isolated from the eyes of Drosophila ° is sepiapterin (Fig. 15-17), in which the pyrazine ring has been reduced in the 7,8 position and a short side chain is present at position 6. Reduction of the carbonyl group of sepiapterin with NaBH4 followed by air oxidation produces biopterin, the most widely distributed of the pterin compormds. 

O Donnell JM, McLean JR, Reynolds ER. 1989. Molecular and developmental genetics of the Punch locus, a pterin biosynthesis gene in Drosophila melano-gaster. Dev. Genet. 10 273-86... 

Einige Jahre spater wurden aus Drosophila mdanogaster eine Reihe von Pterinen isoliert, u.a. das Pterin (VII) (16, 69, 70, 71, 78), das identisch ist mit jenem von Patterson et al. aus menschlichem Ham isolierten und von ihnen bezeichneten Biopterin (43, 44, 45). 

Intimations of an active metabolic role came from a closer examination of insects pterins were also abundant in actively metabolizing tissues. Thus the yellow pterin in the female reproductive ducts and testes sheath of certain races of Drosophila seemed identical with the yellow pigment in the wild-t3q>e eyes (Graf et al., 1955) the tissues generally of Drosophila have a deep violet-blue fluorescence (Hadorn and Schwinck, 1956). Identification... 

There is no clear genetic relation in Drosophila eyes of the water-insoluble ommachrome pigments (derived from kynurenine) and the water-soluble yellow and red pterins (Hadorn, 1956 Hadom and Schwinck, 1956). 

Entirely independent experiments on Drosphila in two different laboratories bolster belief in this parallel action. Knowing that xanthine oxidase from cream converted 2-NHj-4-hydroxypterin to isoxanthopterin, Forrest et d. (1956) identified xanthine oxidase in the pupae of the wild type by the ability of supemates of ground pupae to oxidize this compound to isoxanthopterin, xanthopterin to leucopterin, and xanthine to uric acid. The eye-color mutants (maroon and maroon-like) lacked the enzyme. It becomes apparent why xanthine oxidase should cause parallel changes in pterin eye pigments of Drosophila, and their purines. The rosy mutants of Drosophila are deficient in isoxanthopterin (Hadom, 1956 Hadom and Schwinck, 1956) they should be deficient in xanthine oxidase. As pected, the substrates of the missing enzyme accumulate hypoxanthine and 2-NH2-4-hydroxypteridine in maroon (Glassman et d., 1968), which is also devoid of uric acid, and exactly the same accumulation of hypoxanthine and complete absence of uric acid and isoxanthopterin (Morita, 1968). 

In other Drosophila mutants, deficiency of pterin eye pigments appears to result from lack of substrate, not lack of xanthine oxidase. White-apricot larvae which normally contain very small amounts of 2-NHfe-4-hydroxy-pteridine and isoxanthopterin, produced isoxanthopterin when fed the hy-droxypteridine (Forrest et d., 1956). 

The structure and function of every biologically important pterin is not yet known. Biopterin was isolated recently its formula is presented below. It is a growth substance for the unicellular Crithidia fasciculata. Biopterin is widely distributed in very minute amounts it is found in urine, in Drosophila extracts, and in the food juice of queen bee larvae (royal jelly). The biologic significance of biopterin for bees is still obscure. 

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