Studies on the Membrane-Associated Nature of Human Thyroid Peroxidase: A Difference in the Solubility of the Enzyme from Benign and Malignant Thyroid Tissues*

Abstract

Thyroid peroxidase (TPO) is an integral membrane protein. The intact protein can be solubilized from porcine thyroid 105,000 X g particles (“microsomal” membranes) by Triton X-100 and other nonionic detergents (J Biol Chem 251: 2525, 1976). The Triton X-100 solubilization procedure has now been applied to human thyroid microsomal membranes in an effort to investigate the membrane nature of TPO in thyroid disorders. We studied tissues from 6 patients with thyroid carcinoma (papillary, follicular, and oxyphilic cell), 10 with adenoma (macrofollicular, follicular, microfollicular, and trabecular), 1 with multinodular nontoxic goiter, and 6 with diffuse toxic goiters. Normal tissue was obtained from 4 of the carcinoma patients and 8 of the adenoma patients. TPO activity in thyroid homogenates was determined by the guaiacol assay method. icrosomes from each homogenate were prepared by centrifugation of the 8500 x g supernatant at 105,000 X g for 1 h, and the microsomes were washed hypotonically to release entr...