A study of the structures of the YaYa and YaYc glutathione S-transferases from rat liver cytosol Evidence that the Ya monomer is responsible for lithocholate-binding activity

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Abstract
The 2 dimeric lithocholic acid-binding proteins previously identified as ligandin (YaYa) and glutathione S-transferase B (YaYc) were isolated from rat liver cytosol. These proteins have MW of 44,000 and 47,000, respectively. The recovery of these 2 proteins from liver was not affected by the addition of the proteinase inhibitor Trasylol. No spontaneous interconversion between these 2 proteins was observed on storage. YaYa and YaYc proteins yielded peptides of identical MW after limited digestion with Staphylococcus aureus V8 proteinase. Analytical and preparative tryptic-digest peptide maps showed that all the soluble peptides obtained from YaYa protein were also recovered from YaYc protein. Approximately 6 extra soluble peptides, which were not recovered from YaYa protein, were obtained from the tryptic digest of YaYc protein. Subdigests of the insoluble tryptic-digest cores also resulted in the recovery of identical peptides from both proteins. Evidence is presented that the Ya subunit possessed by both proteins is identical; glutathione S transferase B is a hybrid of ligandin and glutathione S-transferase AA. The Ya monomer is responsible for lithocholate binding.