Galactozymase considered as an adaptive enzyme

Abstract

PREVIOUS studies from this department on adaptive enzymes have been con- cerned with hydrogenlyases. It has been shown that the formation of these enzymes in the Bacteriaceae is controlled by the medium in which the cell is grown, one factor being the presence of the substrate, e.g. formate in the case of formic hydrogenlyase, another being some substance in broth which so stabilises the enzyme that it is active in washed suspensions [Stephenson and Stickland, 1932; The mechanism by which the medium conditions the formation or stabilisation of enzymes was discussed by Yudkin [1932], who postulated two possibilities, either natural selection or chemical adaptation, i.e. direct chemical action of the substrate on the cell. He concluded, chiefly from theoretical considerations, that the production of formic hydrogenlyase by Bact. coli was of the nature of a chemical adaptation. This was later proved by Stephenson and Stickland [1933], who showed that natural selection was not operating, since the enzyme was formed in the absence of cell multiplication.