A cyanogen bromide fragment of beta-galactosidase from Escherichia coli with alpha-donor activity in complementation of the enzyme from mutant M15.

Aminoethylated beta-galactosidase from Escherichia coli was cleaved by CNBr. The fragment C4a was purified by gel filtration and ion-exchange chromatography. The molecular weight of the fragment C4a was determined to be 9000 +/- 600. The N-terminal amino acid was found to be isoleucine. Qualitative examination of homogeneity was carried out by disc-gel electrophoresis. The fragment C4a was shown to be active as an alpha donor in complementation of beta-galactosidase activity in vitro with E. coli mutant M15, which has a deletion in the alpha region of the z gene. The molecular weights of complementable fractions from mutant M15 were found to be 123 000 +/- 2500 and 507 000 +/- 11 000, and of the complemented enzyme 522 500 +/- 11 400.