Inhibition of glycosidases by aldonolactones of corresponding configuration. The specificity of alpha-L-arabinosidase.

1. The previous study (Conchie, Gelman & Levvy, 1967b) of the specificity of beta-glucosidase, beta-galactosidase and beta-d-fucosidase in barley, limpet, almond emulsin and rat epididymis was extended to alpha-l-arabinosidase. 2. The inhibitory action of l-arabinono-(1-->5)-lactone was tested against all four types of enzyme, and alpha-l-arabinosidase was examined for inhibition by glucono-, galactono- and d-fucono-lactone. 3. In emulsin, the enzyme that hydrolyses beta-glucosides, beta-galactosides and beta-d-fucosides also hydrolyses alpha-l-arabinosides. Rat epididymis resembles emulsin except that, as already noted, it lacks beta-glucosidase activity. 4. In the limpet, alpha-l-arabinosidase activity is associated with the enzyme that hydrolyses beta-glucosides and beta-d-fucosides, and not with the separate beta-galactosidase. 5. The effects of the different lactones on the barley preparation suggest that alpha-l-arabinosidase activity is associated with the beta-galactosidase rather than with the enzyme that hydrolyses beta-glucosides and beta-d-fucosides. Fractionation and heat-inactivation experiments indicate that there is also a separate alpha-l-arabinosidase in the preparation.