ENZYME VARIATION IN MICRO‐ORGANISMS

Publisher Website
Google Scholar
Abstract
Summary: The increase in enzyme content in micro‐organisms may be classified according to the type of substance responsible for the increase. First, as has been suggested by Jacoby, the substance may be necessary to the cell as a “brick” for the building up of the enzyme molecule. Secondly, the substance may be the substrate of the enzyme or some closely related compound. A substance in this class may act either directly on the individual cell or as a selecting agent during growth of cells in which the enzyme has appeared as a mutation. Examples of direct chemical interaction between cell and substrate (adaptation) are the hydrogenlyase of Bact. coli and the galactozymase of yeast; examples of mutation and selection occur amongst organisms of the Bact. coli mutabile type.As would be expected, when organisms possessing a newly acquired enzyme are grown in the absence of the substrate, enzymes arising by adaptation are readily lost whilst enzymes arising by mutation and selection tend to be permanent.It would also be expected that the former type of enzyme production would occur in the absence of cell division; for natural selection to operate, however, cell division is essential. Many unsatisfactory attempts have been made to show the dependence or otherwise of certain examples of enzyme production on cell division, such as the study of enzyme production in the presence or absence of suitable growth substances or of poisons. By counting experiments, however, it has been clearly shown that, in the two examples of adaptation quoted, enzyme production occurs in the absence of cell division.Although enzyme production has been obtained in non‐dividing (but untreated) cells, it has not yet been found possible to obtain it in cells which have been rendered non‐viable, that is, incapable of dividing. It would be of interest if such poisoned cells would be found still able to produce the adaptive enzyme, but it is necessary to define carefully the meaning of living cell and growth in relation to micro‐organisms before deciding on the dependence of enzyme production on cell viability or cell growth.Apart from general statements of a teleological nature, the literature contains no general theory of adaptive enzyme production. The “mass‐action” theory of enzyme formation here developed explains the majority of the known facts, is in contradiction with none of them, and allows several deductions to be made which are capable of being tested experimentally.

This publication has 18 references indexed in Scilit: