Investigations on the influence of hemin and hemin derivatives on the nuclear-magnetic relaxation of water protons

Abstract

Haemin, haemin derivatives and ferric haemoproteins are investigated on their influence on the nuclear-magnetic relaxation of water protons. The effectiveness increases in the following order: ferricytochrome c (neutral form), horse methaemoglobin, horse metmyoglobin, cheironomus methaemoglobin, ferricytochrome c (acidic form), haematin. The high effectiveness of the haematin is already decreased by the adsorptive bonding to polyvinylpyrrolidone. The influence on the relaxation of water protons may be divided into a magnetic and a steric component, the latter is thought to be a relative measure for the accessibility of the prosthetic groups in the haemin derivatives. It is shown, that the haemin groups in cytochrome c and cheironomus methaemoglobin are situated at the surface more than those of horse methaemoglobin or horse metmyoglobin. By the bonding of ligands to the horse methaemoglobin the influence of the iron on the relaxation of water protons is attributable not only to the variation of the magnetic moment but also to the variation of the steric arrangement of the prosthetic group to the protein. The methaemoglobin fluoride compound shows especially striking behaviour.