The Subunit Structure of Thiolase

Thiolase from pig heart has been carboxymethylated in 6 M guanidine‐HCl, and the N‐terminal sequence of the carboxymethylated protein is shown to be uniquely Val‐Ser‐Lys. A trypsin digest has been examined by peptide mapping techniques and the number of peptides (42–46) detected is in good agreement with the total number of lysine and arginine residues calculated from the amino acid composition of the enzyme tetramer and assuming 4 identical chains per 170 000 g of protein. No evidence for the presence of more than one type of subunit was found when both the untreated and the carboxymethylated proteines were examined by polyacrylamide and starch gel electrophoresis in 6 M urea. From these results it is proposed that thiolase is composed of four very similar and probably identical protein chains each comprising approximately 400 amino acids including one catalytically active cysteine.