Azotobacter lipoamide dehydrogenase

Bastiaens, P. I. H., van Hoek, A., Benen, J. A., Brochon, J. C. and Visser, A. J. W. G. (1992). Conformational dynamics and intersubunit energy transfer in wild-type and mutant lipoamide dehydrogenase from Azotobacter vinelandii. A multidimensional time-resolved polarized fluorescence study. Biophys. J. 63, 839-53. 

The stability of EH2 is very species dependent. All of the above results refer to the pig heart enzyme and, where tested, to other mammalian species. It was initially reported that no long wavelength absorption was observed upon reduction of E. coli enzyme with NADH 109), but reduction by 1 equivalent of NADH or dihydrolipoamide leads to the formation of 25% of the maximal 2-electron-reduced species 108) and similar results are obtained with the Azotobacter enzyme 114)- That this species is the catalytically important one in the E. coli enzyme as well as in the mammalian enzyme has also been demonstrated 50). Reduction with dihydrolipoamide in the rapid reaction spectrophotometer at 2° results in the full formation of EH2 followed by the slow k = 13 min, 1 mAf dihydrolipoamide) four-electron reduction. The spectrum of EHa generated in this way is shown in Fig. 7 and is identical with that of the pig heart enzyme. The 2-electron-reduced form, EHj of lipoamide dehydrogenase of spinach 99) may be somewhat unstable however, spectrally it is difficult to distinguish between instability and formation of the EHa-NADH complex (see above) on the basis of available spectral data. Either phenomenon could lead to inhibition by excess NADH. In glutathione reductase it is possible that the complex can be rapidly reoxidized by glutathione 53). 

E2 is a catalytic activity found in the pyruvate dehydrogenase complex. It forms the core of the complex. 24 copies of E2 are found in the complex isolated from Azotobacter. E2 is covalently bound to lipoic acid, forming lipoamide. Lipoamide functions to oxidize the aldehyde moiety transferred to it from El to an acetyl group and to subsequently transfer it to coenzyme A, forming acetyl-CoA. 

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See also in sourсe #XX -- [ ]

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