Sur la biosynthese de la β-galactosidase (lactase) chez Escherichia coli. La specificite de l'induction☆

1. 1. The formation of β-galactosidase by E. coli is induced exclusively by substances possessing an intact galactosidic radical. Various inversions or substitutions at one or more positions as well as the suppression of the carbon 6 result in the disappearance of the inductive property. 2. 2. The substances which have the inductive property are not necessarily substrates of the enzyme. Thus certain α-galactosides (melibiose) are inductors yet they are not hydrolysed by β-galactosidase. 3. 3. The inductivity is, in general, independent of the affinity for the affinity for the enzyme. Certain substances (phenyl-β-thiogalactoside) which have a high affinity for β-galactosidase in vitro as in vivo are deprived of the inductive property. 4. 4. The formation of β-galactosidase is inhibited by phenyl-β-D-thiogalactoside, but the inhibition is not competitive, while it should be if it was due to the inhibition of the enzyme. 5. 5. These observations are incompatible with all hypotheses which imply that the induction is connected, either with the activity of the enzyme, or with the formation of a specific complex between the enzyme and the inductor.