Enzymes perform their catalytic action according to mechanisms featuring exquisite specificity, up to the selection of substrate conformers. However, regardless of this high specificity enzymes are able to deal with a repertoire of substrates, whose conversion into reaction products can occur with markedly different rates. Among the factors affecting the velocity of enzyme-catalyzed reactions, the presence in the substrate of an electrostatic charge could be of importance. Here we report on the kinetic parameters of four enzymes (bovine carbonic anhydrase and α-chymotrypsin, Escherichia coli β-galactosidase, and sweet almond β-glucosidase) determined using a NO