PREVIOUS studies from this department on adaptive enzymes have been concerned 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; 1933; Yudkin, 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. In the present study we present some facts connected with the formation of galactozymase, the enzyme complex concerned with the fermentation ofgalactose by S. cerevisiae. The literature already contains material on this subject. Dienert [1900] first recorded the adaptive nature of galactozymase by showing that certain strains of yeast, which at first are unable to grow in media where galactose is the sole carbohydrate, become able to do so if previously grown for a few weeks on a mixture of glucose and galactose. In such cases the same result is achieved by lactose or melibiose, doubtless because these sugars give galactose on hydrolysis.
THE earliest work dealing with the bacterial decomposition of formic acid was that of Hoppe-Seyler [1876], who dealt with its decomposition into carbon dioxide and hydrogen by mixed cultures obtained from mud, and showed that calcium formate was decomposed according to the equation
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