SUMMARY: When cells of growing exponentially in either glucose + mineral salts medium, or lactose + mineral salts (being fully adapted to growth in lactose), are inoculated for the first time into maltose + mineral salts medium containing 10 M-methyl-β-D-thiogalactoside, a very large amount of β-galactosidase is synthesized gratuitously during the lag and early stages of growth in the new medium. The abnormally high enzyme levels are maintained for some time. This is a form of ‘preferential synthesis’, which can be ascribed to a failure of catabolite repression during exposure to an unfamiliar compound as source of carbon and energy. The extent of preferential synthesis is increased by starvation of the organisms prior to inoculation in maltose medium.

Similar experiments involving organisms partially or completely adapted to growth in maltose show a smaller degree, or complete absence, of preferential synthesis and enhanced enzyme levels. The efficiency with which maltose exerts the ‘catabolite repression’ effect is thus a function of the degree of adaptation of the organisms to maltose as sole carbon source.

It is suggested that this breakdown of catabolite repression, followed by its recovery during adaptation, could well be a useful general feature of the adaptive process.


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