-galactosidase-catalysed hydrolysis of -D-galactopyranosyl azide.

1. beta-d-Galactopyranosyl azide is hydrolysed by the beta-galactosidase of Escherichia coli to galactose and azide ion at a mechanistically significant rate. 2. Methyl 1-thio-beta-d-galactopyranoside is a competitive inhibitor of the hydrolysis of the azide and of o-nitrophenyl beta-d-galactopyranoside with K(i) 1.8mm. 3. beta-Galactosidase can thus hydrolyse a range of substrates of general structure beta-d-galactopyranosyl-X(Y), where the atom X has a lone pair of electrons on which the enzyme may act as a Lewis or Brønsted acid, but in which the length of the bond cleaved varies significantly, which is inconsistent with the orbital steering hypothesis.