On the specificity of the D-galactose-binding lectin (PA-I) of Pseudomonas aeruginosa and its strong binding to hydrophobic derivatives of D-galactose and thiogalactose.

The D-galactose-binding lectin (PA-I) from the bacterium Pseudomonas aeruginosa, isolated by affinity chromatography on Sepharose, was examined for its relative affinities for simple sugars and their derivatives using equilibrium dialysis and hemagglutination inhibition tests. The lectin, which was found to bind 0.68 mol of D-galactose per subunit of 12.8 kDa, exhibited an association constant (Ka) of 3.4 x 10(4) M-1 for D-galactose and higher affinities for hydrophobic and thio derivatives of D-galactose (with highest affinity for the hydrophobic thio derivatives). alpha-Methyl-galactoside was a stronger inhibitor than the beta-methyl derivative and alpha-lactose was a weak inhibitor but the hydrophobic phenylated derivatives of the beta-configuration of D-galactose were more potent inhibitors than the respective alpha-galactosides.