Investigation on the induction of the Lac-enzyme. 2. The permeation of galactosylglycerol in Escherichia coli

Abstract

1‐O‐β‐d‐Galactopyranosyl‐d‐glycerol was shown in a previous publication [1] to be an abnormal inducer. It has a maximal activity even at 10−7 M [2] whereby no autocatalytic phase can be observed. On addition of galactose the quoted abnormal behaviour of the inducer galactosyl glycerol is normalized. From these data it was concluded that for this particular case galactose competes with galactosyl glycerol for a lac‐operon independent permease.We could now show that the abnormal behaviour of the inducer galactosyl glycerol also disappears when a bacterial strain is used which lacks the gen MGP for the methyl galactoside permease. This gen maps outside the lac operon of the Escherichia coli chromosome [4] and his expression is constitutive under the conditions of the experiment. In order to prove the responsibility of the methyl galactoside permease for the abnormal behaviour of galactosyl glycerol as inducer we measured the accumulation of galactosyl glycerol in uninduced cells of E. coli K 12 W 3100 and W 3092i, MGP+‐ and MGP−‐strains respectively. It could be shown that in fact the strain W 3100 accumulates galactosyl glycerol whereas the strain W 3092i does not.Since derivatives of galactosyl glycerol are probably the most abundant galactosides in nature it seems likely that galactosyl glycerol is the main natural galactoside substrate during the evolution of the “Lac” operon.