A Comparison of the l-Arabinose- and d-Galactose-binding Proteins of Escherichia coli B/r

Abstract d-Galactose-binding protein was purified from cell-free extracts of Escherichia coli B/r and crystallized using 2-methyl-2,4-pentanediol. This material appeared homogeneous following electrophoresis on polyacrylamide gels in either the presence or absence of sodium dodecyl sulfate. The amino acid composition of this protein was determined and found to be similar to the amino acid composition of d-galactose-binding protein isolated from E. coli K12 but different from the amino acid composition of l-arabinose binding protein from E. coli B/r. Ligand-binding specificities and affinities for the d-galactose-binding protein from E. coli B/r were determined and found to be distinctly different from the ligand-binding characteristics of the l-arabinose-binding protein isolated from the same organism. Peptide map patterns of peptides generated by tryptic digestions of both the d-galactose-binding protein and the l-arabinose-binding protein have demonstrated additional differences between these two proteins. Cross-reactivity was observed between antisera directed against either the d-galactose- or the l-arabinose-binding protein and the heterologous protein, suggesting that although these are two distinctly different proteins, they have some similar structural relationships.