Optical rotatory dispersion of mitochondrial reduced diphosphopyridine nucleotide dehydrogenase from cardiac tissue.

Optical rotatory dispersion spectra of oxidized and reduced FMN and FAD are presented from 600 to 210 rnp and of riboflavin from 600 to 340 mp. Optical rotatory dispersion behavior of soluble DPNH dehydrogenase was studied between 600 and 185 rnp with respect to the oxidation state of the enzyme. The optical rotatory dispersion spectra were analyzed and the extrinsic Cotton effects were resolved from the protein backbone rotations. Shechter-Blout’s A’ parameters were computed: A’193 = 147 and A’225 = -278” for the oxidized enzyme, and A’n3 = 32 and A’22b = -210° for the reduced. The centers of the resolved extrinsic Cotton effects due to nonprotein chromophores were 437 rnh and 350 ml* for the oxidized and 436 rnp and 346 rnp for the reduced enzyme. The rotational strength, amplitude, and band width of these Cotton effects were dependent upon the oxidation state of the enzyme. In addition, anomalous rotations in the region of 550 rnp were also observed but were too small for accurate analysis. These observations indicate that the interactions between the chromophores and the protein are dependent upon the oxidation state of the dehydrogenase. This dependence may be due to changes in geometrical relationships within the system and in the conformation of the protein moiety which is also determined by the oxidation state of the prosthetic groups. These changes may in turn play an intrinsic role in the physiological action of the enzyme for electron transfer in the respiratory chain.