Effect of haematin on the oxidation of succinic acid by tissue preparations

Abstract

Free hematin in a concn. of 2 X 10-4 M inhibits almost completely the oxidation of succinic acid by highly active muscle prepns. In this respect, proto-, hemato- and deutero-hematin are equally effective though neither Fe nor porphy-rins alone produces a comparable effect. When hematin is bound to nitrogenous substances such as glyoxalin or denatured globin, forming the corresponding p-hematin compounds, it loses its inhibitory property. Hence, the prior addition of glyoxalin or denatured protein will protect the enzyme prepn. from inhibition by hematin. Since the oxidation of succinic acid is also inhibited under purely anerobic conditions in presence of methylene blue as hydrogen acceptor and since the oxidation of -phenylenediamine is very little affected, the inhibitory effect is due to a reaction between hematin and succinic dehydrogenase and not to any influence upon the cytochrome system. The inhibition is probably due to the formation of a co-ordination compound between hematin Fe and some groups in succinic dehydrogenase important for its activity.