EVIDENCE FOR PYRROLIDONE CARBOXYLIC ACID IN BETA-GALACTOSIDASE FROM E COLI

Acidic peptides isolated from pronase digests of β-galactosidase by chromatography on Dowex 50-X2 contain N-terminal pyrrolidone carboxylic acid. This was not due to cyclization of glutamine or glutamic acid to pyrrolidone carboxylic acid during the procedure as addition of excess fluorodinitrobenzene immediately following digestion and prior to the chromatographic step did not alter the results. Acetylation of β-galactosidase prior to the procedure resulted in recovery of additional amino acids which were compatible with the previously established N-terminal threonine. These data indicate the presence of multiple polypeptide chains in the β-galactosidase monomers of 135,000 molecular weight, with pyrrolidone carboxylic acid and threonine as N-terminal residues. © 1969.