Lipoyl dehydrogenase

The low molecular weight form of mitochondrial NADH dehydrogenase was first isolated from pig heart muscle by Edelhoch et al. (60) and Mahler and his associates 57 in 1952. The mitochondrial origin of the enzyme was demonstrated by de Bernard 81. These and similar preparations reported subsequently by Mackler 63, Kumar et al. 63, and Pharo et al. 64 were isolated by extracting the source material (heart muscle or various submitochondrial preparations) with 9-11% ethanol at pH 4.8-5.S and 43°-45°, a procedure originally devised for isolation of the Straub diaphorase (lipoyl dehydrogenase) 85. Two other preparations of basically similar composition and catalytic proper-... 

Lipoamide reductase (NADH). E3 component of alpha-ketoacid dehydrogenase complexes. Lipoyl dehydrogenase. Dihydrolipoyl dehydrogenase. 

S-C-CHj on iip0ic acid (3) xhe acetyl group is then transferred by the same subunit to coenzyme A, which diffuses from this complex to the total mitochondrial matrix. (4) The lipoic acid containing the subunit now has lipoic acid with two SH groups and must be reoxidized back to the S-S form. This is catalyzed by another subunit lipoyl dehydrogenase, which contains a covalently bound prosthetic group of FAD. This enzyme catalyzes the... 

Fig. 5. Lipoyl dehydrogenase and respiratory decline in rat liver homogenates...

Highly purified lipoyl dehydrogenase preparations from various sources have been analyzed for selenium. The values obtained show clearly that the element is not present in stoichiometric amounts. For example, 7 g of selenium were found per gram of a highly purified Upoyl dehydrogenase preparation. This level is 10-20 times higher than those detected in a... 

Concerning lipoyl dehydrogenase, Kosower has recently suggested that the red intermediate observed during the reduction of this enzyme is a complex of mercaptide and FAD (XIX). Searls and Sanadi " claimed to have detected a similar complex in a reaction between dihydrothioctate (XX) and FMN. An intensification of the orange tinge of the solution was observed immediately... 

Amino acid sequences of dithiol-disulphide centres Lipoyl dehydrogenase val-cys-ieu-asn-val-gly-cys ilu-pro-ser... 

The sequences of the dithiol active centres of two enzymes of this type from E. coli have recently been reported . The lipoyl dehydrogenase dithiol peptide has four amino acids intervening between the two cysteines and is rich in hydrophobic amino acids. This has been taken as a reflection of a highly hydrophobic pocket at the catalytic centre, as had been implicated by model substrate studies. The thioredoxin reductase dithiol... 

Tatsumi, K., N. Koga, S. Kitamura, H. Yoshimura, P. Wardman, and Y. Kato. 1979. Enzymic cis-trans isomerization of nitrofiiran derivatives - isomerizing activity of xanthine oxidase, lipoyl dehydrogenase, DT-diaphorase and liver microsomes. Biochim. Biophys. Acta 567 75-87. 

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