8- Hydroxy-5-deazaflavin

Scheme 2 Mechanism of repair of cyclobutane pyrimidine dimers (CPD) by a CPD photolyase. 8-HDF 8-hydroxy-5-deazaflavin, ET electron transfer. FADH reduced and de-protonated flavin-coenzyme...

Alex, L. A., Reeve, J. N., Orme-Johnson, W. H. and Walsh, C. T. (1990) Cloning, sequence determination, and expression of the genes encoding the subunits of the nickel-containing 8-hydroxy-5-deazaflavin reducing hydrogenase from Methanobacterium thermoautotrophicum delta H. Biochemistry, 29, 7237-44. 

Michel, R., Massanz, C., Kostka, S., Richter, M. and Fiebig, K. (1995) Biochemical characterization of the 8-hydroxy-5-deazaflavin-reactive hydrogenase from Methanosarcina barkeri Fusaro. Eur. J. Biochem., 233, 727-35. 

Muth, E., Morschel, E. and Klein, A. (1987) Purification and characterization of an 8-hydroxy-5-deazaflavin- reducing hydrogenase from the archaebacterium Methanococcus voltae. Eur. J. Biochem., 169, 571-7. 

Several selenoproteins have been found in certain bacteria and archaea. A hydrogenase from Methano-coccus vannielii contains selenocysteine.559 560 This enzyme transfers electrons from H2 to the C-5 si face of the 8-hydroxy-5-deazaflavin cofactor F q (Section B,4). The same bacterium synthesizes two formate dehydrogenases (see Fig 15-23), one of which contains Se. Two Se-containing formate dehydrogenases are made by E. coli. One of them, which is coupled to a hydrogenase in the formate hydrogen-lyase system (see Eq. 15-37), is a 715-residue protein containing selenocysteine at position 140.561-563 The second has selenocysteine at position 196 and functions with a nitrate reductase in anaerobic nitrate respiration.561... 

The three-pulse electron spin-echo envelope modulation (ESEEM) technique is particularly sensitive for detecting hyperfine couplings to nuclei with a weak nuclear moment, such as 14N. It has been used to probe the coordination state of nickel in two hydrogenases from M. tkermoautotrophicum, strain AH (56). One of these enzymes contains FAD and catalyzes the reduction of F420 (7,8-dimethyl-8-hydroxy-5-deazaflavin), while the other contains no FAD and has so far only been shown to reduce artificial redox agents such as methyl viologen. 

Biosynthesis of 7,8-didemethyl-8-hydroxy-5-deazaflavin starts from guanosine-5 -triphosphate (GTP), which leads through several steps to 5-amino(6-ribitylamino)-2,4( 1 //,3//)-pyrimidinedione 5 -phosphate, whose addition to 4-hydroxybenzoic acid which comes from shikimate gave the target compound <85JA8300>. The biosynthesis of riboflavin and deazaflavins has been studied in Methanobacterium thermoautotrophicum <91JBC9622>. 

Pai and co-workers recently developed a general strategy for determining the stereochemistries of the flavoenzymes that is fundamentally based on the stereochemical features of the glutathione reductase reaction (87, 88). Their experimental approach relies on the observations that (1) the reduced forms of the 8-demethyl-8-hydroxy-5-deazaflavins (7) are not susceptible to nonenzymic racemization,... 

Photoreactivating enzyme contains two chromophores. (A chromophore is a structural moiety that absorbs light of characteristic wavelengths.) One chromophore is flavin adenine dinucleotide in the reduced state, FADH". The second chromophore in some photolyases is 5,10-methenyltetrahydrofolate and in others is 8-hydroxy-5-deazaflavin. 

Methenyltetrahydrofolate - A molecule that acts like 8-hydroxy-5-deazaflavin in DNA photolyases. It acts as a light harvesting factor. 

---