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Binding of substituted phenyl 1-thio-β-D-galactopyranosides to β-D-galactosidase from e.

The binding of a series of substituted phenyl 1-thio-β-D-galactopyranosides to the active site ofβ-D-galactosidase from E. coli has been investigated. The inhibition constants and the standard free energy of transfer ΔG°(K1) were compared with the partition coeficients and ΔG° (1-octanol) values of these inhibitor molecules in a model 1-octanol-water system. All of the evidence available suggests that the aglycon group of the inhibitor is bound to the active site unspecific, hydrophobic forces. Correlations between ΔG° (K1) and ΔG° (1-octanol) could not be found for the whole series, but only for simpler sub-series. Probably, the octanol system is too incomplete a model for the hydrophobic region in the active site ofβ-D-galactosidase.