Structural studies on stem bromelain. Cyanogen bromide cleavage and amino acid sequence of carboxyl-terminal half of the molecule.

Stem bromelain was cleaved with cyanogen bromide, and the products were fractionated with and without prior maleylation and sulfitolysis. The fragments that corresponded to the carboxyl-terminal half of the molecule were isolated and nearly completely sequenced. This portion of the enzyme molecule contained one disulfide linkage. A specific cleavage at the amino peptide bonds of that cystine residue by reduction, modification into S-cyano derivatives and exposure to alkali gave important information of the amino terminal sequence. By combining the present data with the previously known partial sequence of the parent molecule, 101 amino acid residues were aligned down to the carboxyl terminus and compared with those of papain. The sequence homology between carboxyl-terminal halves of these two thiol proteases of plant origin was found to be 34.7%.