AMINO-ACID-COMPOSITION OF PROTEINS EXTRACTED FROM ENDEMIC GOITER GLANDS

Proteins were isolated and characterized in thyroid tissue of six pati ents from Brazil with endemic goiter. Biochemical studies of these thy roidal proteins included gel filtration, electrophoresis, and amino ac id analysis. In addition to thyroglobulin, two of the most abundant pr oteins found in all goiters studied had molecular weights of 68 and 14 kDa, One protein was identified as albumin based on its immunoreactiv ity with antibodies to serum albumin. The other protein was identified as a hemoglobin subunit using reverse-phase high-performance liquid c hromatography (HPLC). Identification was confirmed by partial N-termin al amino acid sequencing that showed several nonconservative differenc es in thyroid albumin when compared to human serum albumin (HSA). Bioc hemical findings were correlated with iodine and hormone contents in s erum and thyroglobulin from these patients. Based on these findings, w e suggest that hemoglobin and albumin are taken up from the blood by t he hyperplastic thyroid tissue, Albumin would be processed by the thyr oid follicular cell, becoming iodinated and released into the circulat ion.