THE IN VITRO FORMATION OF IODINATED COMPOUNDS BY THYROID SLICES AND HOMOGENATE PREPARATIONS

Abstract

The protein-binding capacity of sheep thyroid tissue slices varied widely from gland to gland and increased with the length of time the tissue was incubated with radioactive I. The distribution of labeled I between diiodotyrosine (DIT) and moniodotyrosine (MIT) usually reached an equilibrium after 2-3 hr. of incubation. The protein-binding capacity of the mitochondria-microsomes fraction of sheep thyroid tissue varied widely between samples; in some experiments as much as 20% of the total labeled I became protein-bound. Only MIT could be demonstrated in the sub-cellular fractions. Experimental conditions designed to promote protein synthesis failed to enhance the formation of protein-bound I131 or of iodothyronines, either in slices or in particulate fraction preparations. Several unidentified iodinated substances were formed by both slices and homogenate preparations. The addition of diphosphopyridine nucleotide to saline extracts of thyroid tissue did not promote the formation of iodothyronines.