The induced synthesis of β-galactosidase in E.coli I. Synthesis of enzyme under various experimental conditions

Abstract

In E. coli the content of β-galactosidase in already adapted cells corresponds to a hydrolysis of about 2 μ M ONPG × min −1 per mg dry weight. In adpating cells the enzyme is synthesized during the lag phase, and during the early growth phase the amount of enzyme synthesized per mg dry weight of new cells considerably exceeds the value mentioned above. By growing the bacteria in the presence of both glucose and lactose (diauxie), it was shown that the time of growth initiation is not solely a function of the amount of enzyme present in the cells. Induction of β-galactosidase synthesis occurs even in the absence of any exogenous nitrogen source, at least when lactose is the only energy source. Under these conditions the extent of enzyme synthesis may be decreased by starvation, by extraction with water and by pretreatment with glucose. However, the synthetic capacity may be recovered, partly at least, by addition of nitrogen-containing substances such as alanine and ATP. The initial rate of enzyme synthesis in N-free medium is also reduced by starvation and by extraction with water. Addition of small amounts of glucose, alanine or ATP, as well as pre-treatment with glucose or lactose increases this rate.