Circular dichroism spectra of NADH-cytochrome b5 reductase purified from rabbit erythrocytes.

Soluble oxidized NADH-cytochrome b5 reductase from rabbit erythrocytes showed characteristic negative CD bands at 285 and 460-490 nm and positive CD bands at 310 and 370-390 nm. By the anaerobic reduction of the enzyme with NADH, the sign of the CD spectrum was reversed. The CD spectrum of the NADPH-reduced enzyme was different from that of the NADH-reduced one and was closely similar to that of the dithionite-reduced one. Modifications of cysteine or tyrosine residues in the enzyme were shown to cause no release of flavin or to weaken the binding of flavin, as compared to the immediate release of flavin with HC1 or NaOH.