Tissue Respiration and Endocrine Function. IV. Influence of Thyroidectomy on Succinoxidase Activity of Surviving Tissues. ∗

Abstract

The oxidation of succinic acid is a very suitable reaction for studying the oxidation capacity or respiration of a tissue, particularly muscle. Einbeck, 1 Moyle, 2 and others have shown that perfectly fresh muscle normally contains succinic acid; Thunberg, 3 Batelli and Stern, 4 et al., have demonstrated in muscle and other tissues a very powerful enzyme for the oxidation of this acid; the activity of this enzyme is not diminished, in fact may be enhanced, by washing the tissues, a procedure which almost completely inhibits the action of other oxidizing systems either by its direct action upon the enzyme systems or by removing their normal substrates; and lastly, through the work of Thunberg, Einbeck and Fleisch 5 we are familiar with the details of the chemical changes occurring in this oxidative reaction. These investigators have shown that when succinic acid, C₄H₆O₄, is oxidized by the tissues it is transformed to fumaric acid, C₄H₄O₄, one atom of oxygen reacting with each molecule of the acid without the addition of water. Fleisch has further shown that the succinoxidase is probably composed of a dehydrogenase which is capable of transporting active hydrogen to any suitable acceptor, e. g., active oxygen, methylene blue, etc., but before the former can function as a hydrogen acceptor it must first be activated by another enzyme. Warburg 6 believes that this depends upon the presence of iron. The oxygen activator only is inhibited by HCN.

The utility of this reaction lies especially in the fact that, through washing of the finely minced tissue, sucinoxidase can be studied alone since succinic acid, in the form of its sodium salt, can be added to the substrate in optimum concentrations.