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The Physiology and Genetic Significance of Enzymatic Adaptation

1945; Missouri Botanical Garden; Volume: 32; Issue: 2 Linguagem: Inglês

10.2307/2394254

2162-4372

S. Spiegelman,

Metabolism and Genetic Disorders

THE PHENOMENON OF ADAPTATION Wortmann (1882) showed that certain bacterial species could produce .nylaseonly when grown in the presence of starch.Since these early observations many more of a similar nature have been made.The bacteriological literae re-ture in particular contains innumerable instances of so-called "training" phenomena of the most varied kinds.Recent reviews by Karstrom ('38), Yudkin ('38), Rahn ('38), Stephenson ('39), Linderstrom-Lang ('40), Dubos ('40), and Gale ('43) summarize the available data.The essentials of the phenomenon may be stated in the following terms: a population of cells placed in contact with some substrate acquires, after the lapse of some time, the enzymes necessary to metabolize the added substrate.Th moval of the substrate leads to the disappearance of the enzyme system it evoked.Karstrom ('38) designated as "adaptive" those enzymes which are produced as a specific response to the presence of the homologous substrate.Such enzymes were differentiated from the "constitutive" ones which are always formed by the cells of a given species, regardless of the presence or absence of their homologous substrates.Because of its convenience, Karstrom's terminology has been widely adopted.In recent years, however, it has become increasingly clear that it is not adequate for the description of the facts.In the first place, the classification raises the obvious difficulty that the ease with which a given enzyme is detected in low amounts will determine the category in which it is placed.In addition, enzymes which have been labeled constitutive undergo wide fluctuations in the presence and absence of their substrate.Thus, the invertase content of B. colt rises to 452 (Stephenson, '39) in the presence of sucrose and falls to values lying 12.4 and 39 in its absence.Again the Q , lucose value of B. colt is about 1,000 for organisms grown in the presence of glucose and about 190 for those grown in lactate medium (Stephenson and Gale, '37).In all carefully examined instances where enzymesubstrate relations are known, substrate has stimulated or stabilized its enzyme.The only claim for independence of enzyme level from its substrate was made by Quastel ('37), who reported that glucose stimulated urease formation whereas urea suppressed it.However, Epps and Gale ('42) reinvestigated the problem and showed that the differences Quastel observed depended on the fact that ex-1 Certain of the investigations reported here were aided by a grant from the Penrose Fund of the American Philosophical Society.Grateful acknowledgment is also made