Optical rotatory dispersion and circular dichroism of D-amino acid oxidase.

Abstract

Abstract The optical rotatory dispersion and circular dichroism of d -amino acid oxidase ( d -amino acid: O 2 oxidoreductase, EC 1.4.3.3, pig kidney) were measured. In the visible region, the holoenzyme showed anomalous dispersion curves with characteristic patterns depending on the state of the coenzyme (FAD or FADH 2 ). The presence of optically active absorption bands was confirmed by measurement of circular dichroism. The anomaly in the disperison curves can be explained by assuming that weak Cotton effects, due to chromophores of the bound coenzyme, are superimposed on the intrinsic dispersion curves of the protein moiety of the enzyme. A plain dispersion curve was observed with the apoenzyme, and it differed significantly from the dispersion curve presumed for the protein moiety of the holoenzyme. In the far-ultraviolet region, the apoenzyme and holoenzyme exhibited identical optical rotatory dispersion and circular dichroism. It is concluded that the two forms of holoenzyme have almost the same conformation, and removal of the coenzyme produces a reversible conformational change in the non-α-helical portion of the protein moiety of the enzyme.