Circular dichroism studies of myoglobin and cytochrome c derivatives

Abstract The natural and magnetic circular dichroism of the following compounds were measured in the visible region: sperm whale ferrimyoglobin and its cyanide, azide, fluoride, hydroxide, thyocyanate, nitrite and nitric oxide derivatives; sperm whale ferromyoglobin and its carbonyl, oxy and nitric oxide derivatives; horse heart ferricytochrome c , ferri- and ferronitric oxide cytochrome c . The circular dichroism reveals the splitting of Q 0 and Q 1 absorption bands, suggesting that in carbonyl ferromyoglobin, azide, nitric oxide ferrimyoglobin and nitric oxide ferricytochrome c the ligand forms a non-linear ironligand bond. The same conclusion may be given with oxy ferromyoglobin but is more ambiguous in this case. The contributions from the A, B and C terms to the magnetic circular dichroism are tentatively analysed.