ON THE ORIGIN OF THE CARBON IN THE INDUCED SYNTHESIS β-GALACTOSIDASE IN ESCHERICHIA COLI

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Abstract
Experiments were designed to test the following 2 possibilities for synthesis of beta-galactosidase by Escherichia coli (a) precursor + free amino acids[forward arrow]active enzyme. (b) free amino acids[forward arrow]active enzyme. Enzyme synthesis was induced in cells uniformly labeled with C14 while they were suspended in unlabeled medium. Isolation and purification of the beta-galactosidase synthesized revealed that less than one% of its carbon could have been derived from any cellular components existing prior to the moment of addition of the inducer. These findings virtually eliminate any hypothesis which presupposes the preexistence of precursor material convertible into enzyme. The data further indicate that protein synthesis in the growing E. coli cell is virtually irreversible. Protein "turnover" even remotely approximating the synthetic rate could not be detected.