Pyridine Nucleotides in the Thyroid. V. An Artifactual Effect of Thyroid Stimulating Hormone in Thyroid Homogenate

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Abstract
The factors which influence the oxidation of 6-phosphogluconate-1-C14 by thyroid homogenate have been investigated. In a system in which C14O2 production was not increased by addition of 6-phosphogluconic dehydrogenase, augmented oxidation was observed when ATP and DPN were added, consistent with the presence of DPN kinase activity and generation of TPN. With constant amounts of ATP and DPN, the addition of increasing quantities of partially purified liver DPN kinase was associated with greater C14O2 production. Two "crude" preparations of TSH (thyroid stimulating hormone) increased decarboxylation of 6-phosphogluconate-1-C14 in thyroid homogenate both with and without added ATP and DPN, but this effect could not be reproduced using more purified preparations of TSH. Furthermore, it was not specific, since the "crude" TSH also stimulated C14C2 production using rat testis homogenate. Despite this difference between the "crude" and more purified TSH using thyroid homogenates, both hormones equally increased glucose oxidation and TPN levels in thyroid slices. These studies clearly demonstrate the importance of using purified preparations of substances before attributing effects to them.