Metabolic Characteristics of Preparations of Isolated Sheep Thyroid Gland Cells. III. Oxidation of Substrates Involved in Carbohydrate Metabolism and the Krebs Cycle

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Abstract
The ability of sheep thyroid cells, isolated from follicles by a continuous-flow trypsinization procedure, to oxidize various carbons (C14-labeled) of glucose, lactate, pyruvate and alanine to CO2 was studied. The extent of conversion of each carbon to CO2 expressed per mg protein, by the isolated cells exceeded that by slices. Such findings reflect the higher specific activities of glycolytic and Krebs cycle enzymes previously reported for cells than for slices. The addition of methylene blue to the medium increased the conversion of carbon 1 of glucose to CO2 much more than it did that of the 6th carbon. The effect of this oxidation-reduction mediator was enhanced by the presence of thyrotropic hormone in the medium. The oxidative patterns observed with C14-labeled glucose, lactate, pyruvate and alanine in the experiments with isolated cells did not differ significantly from those observed with slices. This and other evidence cited further attest to the usefulness of the isolated cell preparation for the study of metabolic properties of the parenchymal cell of the thyroid gland. The values observed for the cl4O2 ratios of [image], [image], [image] and [image] demonstrate that the Krebs cycle operates in thyroid tissue. Analysis of the ratios of the Cl4O2 yields from the [alpha] and [beta] carbons of lactate and pyruvate as well as from the carboxyl and methyl carbons of acetate revealed that this cycle not only operates in the thyroid cell as a terminal oxidative pathway but, in addition, provides a synthetic function.