Multiple Forms of Phosphodeoxyribomutase from Escherichia Coli. Physical and Chemical Characterization

Phosphodeoxyribomutase from Escherichia coli has been purified to homogeneity. Chromatography on DEAE-Sephadex revealed three peaks of enzyme activity, designated form I, form II, and form III. Form III could be further separated into form III-1 and form III-2 by polyacrylamide gel electrophoresis. The four different molecular forms of the enzyme thus isolated were shown not to be products of the column chromatography per se. The amino acid composition as well as the N-terminal amino acid were found to be identical for the different forms. Molecular weight determinations demonstrated that all four forms of the enzyme consist of a single polypeptide chain with a molecular weight of 45,000 plus or minus 1000. Measurements of partial specific volumes, sedimentation coefficients, and absorption coefficients for form I and form II did not reveal any differences. It is concluded that the multiple forms of phosphodeoxyribomutase are caused by modifications of the polypeptide chain. Evidence is presented that form II is formed in vitro from form I by deamidation. It is probable that this deamidation occurs in vivo also. The different forms displayed only minor changes with respect to KM for substrate and cofactor. Greater differences seem to exist among the four enzyme forms with respect to VM and to cobalt binding.