Galactozymase considered as an adaptive enzyme

Abstract

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.

Adaptive Variation in the Level of Oxidative Activity in Saccharomyces cerevisiae

“…The adaptation of yeast and other micro-organisms to the utilization of galactose or other saccharides has been widely employed as the test system in studies on the mechanisms of enzymic adaptation (Stephenson & Yudkin, 1936;Monod, 1942;Spiegelman, 1946). Such adaptations involve the formation of enzymes for the conversion of these sugars into intermediates of glucose or ribose metabolism; the existence of independent routes for metabolism of other sugars has not been clearly demonstrated.…”

The Adaptive Metabolism of D-Galactose in Aspergillus nidulans

“…Comparison of these results for A. nidulans with the classical work of Stephenson on Escherichia coli (Stephenson, 1949) and Saccharomyces cerevisiae (Stephenson & Yudkin, 1936) reveals similarity of the overall metabolism of galactose in all three organisms. Relative to glucose, galactose is a poor carbon source for growth; it is oxidized by galactose-grown organisms at about one half the rate of glucose and the enzyme systems are inducible.…”

Perspectiva histórica del origen evolutivo de la resistencia a antibióticos

“…Para dar una explicación más rigurosa a lo planteado por Dienert y Monod, Stephenson y Yudkin enfatizaron en la fisiología, postulando que las bacterias adaptaban su maquinaria metabólica a las oportunidades ambientales (Dienert, 1900;Stephenson & Yudkin, 1936;Yudkin, 1936). Así, analizaron ¿En qué condiciones se desarrollaban las enzimas que fermentaban galactosa y glucosa en E. coli y qué relación había entre la formación, actividad enzimática y multiplicación celular?…”