Enhanced Oxidation of α-Glycerophosphate by Mitochondria of Thyroid-fed Rats

Abstract

That the enhanced metabolic rate of hyperthyroid animals is reflected in an increased rate of oxygen consumption by the excised tissues of such animals was discovered by Rohrer (1) in 1924. Since that time many investigators have sought an explanation of this phenomenon by comparing the activity of various respiratory enzymes in tissues from normal and hyperthyroid rats. The results of such studies were summarized by Barker (2) in 1951. More recent work has demonstrated that hyperthyroidism results in increases of cytochrome oxidase (3,4), the rate of oxidation of several substrates by mitochondria (4,5), adenosine triphosphatase (4)) and of reduced triphosphopyridine nucleotide-cytochrome c reductase (6). The reported increases range from those which are barely significant to two times the normal activity. The present paper describes the large increase in rate of (Yglycerophosphate oxidation by mitochondria from rats fed desiccated thyroid. It is shown that the increase in activity pertains only to the “particulate” ar-glycerophosphate dehydrogenase of hepatic mitochondria and not that of the diphosphopyridine nucleotide-linked dehydrogenase found in the soluble fraction. Attempts are made to clarify the mechanism of this huge increase in enzymatic activity.