Complex biopterin

Quercetinase, 44 281 Quinlol complexes, osmium, 37 270 1,5-Quinoid-7,8-dihydro-6//-L-biopterin, pro-tonated, oxo-Mo(IV) complex, 40 11-12 Quinone complexes... 

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... 

Such copper complexes may serve as models for Cu biopterin complexes found in some metalloenzymes similarly, PhenoxSQ complexes of iron may resemble partially reduced iron-biopterin species. 

Figure 19-6. Hypothetical active site complex of phenylalanine hydroxylase. The nonheme iron atom of phenylalanine hydroxylase is coordinated with protein amino acid residues (top of the figure) and molecular oxygen. The BH4 cofactor is also coordinated with molecular oxygen (bottom of the figure). It has been suggested that this complex decomposes to either an iron-oxygen complex or a biopterin-4 hydroperoxide complex prior to interaction with the amino acid substrate.

Fischer et al. (62) have shown that tetrahydro-L-biopterin reacts with Mo 02Cl2 to give 16 (Fig. 2), which is formulated as an oxo-Mo(IV) complex of protonated l,5-quinoid-7,8-dihydro-6/f-L-biopterin. The short N(5)—C(4a) bond distance (1.334(8) A), the long N(5)—C(6) dis-... 

No I all cofaclyrs are derived from vitamins, Coenzyme Q, lipoic acid, dolichol phosphate, biopterin, heme, and molybdopterin are cofactors that are synthesized in the body from simple organic compounds. Heme and molybdopterin are relatively complex, from a nutritional point of view, because they require metal ions as part of their structure. 

Reactions of Mo02Cl2 with the dihydrochlorides of 6/ -tetrahydro-i-biopterin, I I4Ijl (267),631 tetrahydropterin, H4P2 (268, R = H),632 or tetrahydro-6,7-dimethylpterin, H4P3 (268, R = Me)633,634 produce red-purple complexes, now formulated as trihydropterin species,... 

McTigue, M. a., Davles, J. E., II, Kaufman, B. T., Kraut, J. (1992) Crystal Structures of Chicken Liver Dihydrofolate Reductase Complexed with NADP and Biopterin, Biochemistry 31, 7264—7273. 

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