Thymine-7-hydroxylase

Wondrack LM, C-A Hsu, MT Abbott (1978) Thymine-7-hydroxylase and pyrimidine deoxyribonucleoside 2 -hydroxylase activities m Rhodotorula glutinis. J Biol Chem 253 6511-6515. 

Wetzstein H-G, N Schmeer, W Karl (1997) Degradation of the fluoroquinolone enrofloxacin by the brown-rot fungus Gleophyllum striatum identification of metabolites. Appl Environ Microbiol 63 4272-4281. Wondrack LM, C-A Hsu, MT Abbott (1978) Thymine-7-hydroxylase and pyrimidine deoxyribonucleoside 2 -hydroxylase activities in Rhodotorula glutinis. J Biol Chem 253 6511-6515. 

An elegant study by Ortiz de Montellano and Kunze strongly suggests that oxirenes are formed as intermediates in the oxidation of alkynes by microsomes <80JA7373>. 5-Ethynyluracil has been shown to act as a potent mechanism-based inhibitor of thymine 7-hydroxylase, an a-ketoglutarate dioxygenase the intermediacy of an oxirene has been proposed for the inactivation mechanism... 

Bankel, L., G. Lindstedt, and S. Lindstedt Thymine 7-Hydroxylase from Neuro-spora crassa. Substrate Specificity Studies. Biochim. Biophys. Acta 481, 431 (1977). 

Holme, E. A Kinetic Study of Thymine 7-Hydroxylase from Neurospora crassa. Biochem. 14, 4999 (1975). 

Thymine, 2-oxoglutarate oxygen oxidoreductase (7-hydroxylating), or Thymine, 2-oxoglutarate dioxygenase, or Thymine 7-hydroxylase (EC 1.14.11.6). (The dioxygenase of EC number 1.14.11.5 has now been deleted from the EC list). 

This mechanism is consistent with a number of observations. Kinetic studies on prolyl 4-hydroxylase [223] and thymine hydroxylase (EC 1.14.11.6) [224] suggest that cofactor binds first, followed by 02. The bound 02 appears to have superoxide character, as superoxide scavengers are competitive inhibitors of 02 consumption [225,226], It is also clear that the oxidative decarboxylation of the keto acid is a distinct phase of the mechanism from the alkane functionalization step, as these two phases can be uncoupled, particularly when poor substrate analogs are employed [227-229], Evidence for an Fe(IV) = 0 intermediate derives from studies with substrate analogs. Besides the hydroxylation of the 5-methyl group of thymine, thymine hydroxylase can also catalyze ally lie hydrox-ylations, epoxidation of olefins, oxidation of sulfides to sulfoxides, and N-de-... 

All the enzymes contain ferrous iron. Ferrous ions are essential for the catalytic activity of butyrobetaine hydroxylase (259), proline-4- 254) and 3- 242, 243), hydroxylases, thymidine hydroxylase 260), lysine hydroxylase 261), trimethyllysine hydroxylase 247), thymine oxygenase 262—264), cephalosporin hydroxylase 249), and hydroxy-phenylpyruvate 265—267). In addition, the enzymes show a non-stoichio-metric requirement for ascorbic acid which is supposed to maintain the ion co-factor in the ferrous oxidation state (2, 242, 243, 254). Labelling studies with butyrobetaine hydroxylase 268), proline-4-hydroxylase 269), thymine oxygenase (270), cephalosporin hydroxylase (257) and hydroxy-phenylpyruvate hydroxylase (277) all indicate a common pattern of oxygen incorporation. One atom of oxygen becomes the new hydroxyl group while the other is located in one of the carboxylic acid groups of succinic acid. 

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