Hydroxybutyryl-CoA Dehydrase

2 4-Hydroxybutyryl-CoA Dehydrase. - 4-Hydroxybutyryl-CoA dehydratase catalyses the reversible dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA, which involves cleavage of an unactivated P-C-H bond. The enzyme also catalyses the apparently irreversible isomerization of vinylacetyl-CoA to crotonyl-CoA. The enzyme has been described as homotetramer with M, 56 kDa per subunit. It is thought to contain two molecules of FAD and one [4Fe-4S] cluster per homotetramer. 

Miih and co-workers have characterized 4-hydroxybutyryl-CoA dehydrase from Clostridium aminobutyricum by optical spectroscopy and EPR. The EPR spectrum of active dehydratase showed essentially no signal at 100 K. When the enzyme was reduced such that the optical spectrum indicated the presence of a flavin radical. An EPR signal, with g = 2.0014, was detected at the same temperature. It showed no hyperfine structure and had a linewidth of 2 mT, characteristic for a neutral flavin radical, and could be easily saturated at lower temperatures. When the FAD was photoreduced further to the hydroquinone the EPR signal disappeared. 

In the same contribution, ENDOR was performed on this spedes. For the SotCHs group, Aiso = 8.5 MHz with Ax = 7.9 MHz and A = 9.69 MHz could be determined. This coupling increased to Atso = 8.38 MHz with A = 9.0 MHz and A = 10.24 MHz when substrate, 4-hydroxybutyryl-CoA, is bound. The central crossing point of the C6H hfc could also be identified. It showed no difference in the presence or absence of substrate and had a value of 6.23 MHz. 

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