Partial reduction of disulfide bonds in the hormone-specific subunits of TSH and LH

Abstract

Partial reduction at pH 7.0 of the hormone specific (β) subunit of either bovine thyrotropin or luteinizing hormone with dithioerythritol results primarily in the opening of a single disulfide bridge. The partially reduced subunits were alkylated with [1- 14C] iodoacetic acid, followed by complete reduction and alkylation with non-radioactive iodoacetic acid. Isolation and degradation of the radioactive tryptic peptides shows that the bond primarily reduced in each β subunit links analogous half-cystine residues in the two sequences (88–95 in TSH-β and 93–100 in LH-β). These results are the first direct evidence of similar disulfide structures in hormone specific subunits of glycoprotein hormones.