Abstract
Reactions of pig heart lipoamide dehydrogenase with pyridine nucleotides. Evidence for an effector role for bound oxidized pyridine nucleotide.
Highlights
Stopped flow kinetic measurements of the reduction of oxidized enzyme by saturating levels of NHDH and APyADH have demonstrated an intermediate which appears to be a complex of oxidized enzyme and reduced pyridine nucleotide
Since thiolate to flavin charge transfer is maximal at 530 nm in EH, the shift in charge transfer absorbance associated with the binding of oxidized pyridine nucleotide may reflect an alteration in the oxidation-reduction potentials of flavin and disulfide/dithiol
We suggest that bound oxidized pyridine nucleotide may function as an acceptor of reducing equivalents from EH2, and as an effector which influences flavin-disulfide interaction in EH2
Summary
(Received for publication, October 2, 1978, and in revised form, January 8, 1979). P. (Equation l), is thought to function primarily in the second half-reaction, Equation 2, where it presumably mediates the transfer of electrons between the oxidation-reduction-active disulfide and pyridine nucleotide [3] This assumption is supported by x-ray data on the closely related enzyme, red cell glutathione reductase [7], which shows the flavin located between the oxidation-reduction-active disulfide and the bound oxidized pyridine nucleotide. We began these studies in the hope of identifying intermediates in the pyridine nucleotide half-reaction. It is possible that the sequence of electron transfers in native enzyme is more or less concerted, so that distinct intermediates will not be observed
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