Abstract
Diauxie is at the origin of research that led Jacques Monod (1910–1976), François Jacob (1920–2013), and André Lwoff (1902–1994) to win the Nobel Prize in Physiology or Medicine in 1965 for their description of the first genetic regulatory model. Diauxie is a term coined by Jacques Monod in 1941 in his doctoral dissertation that refers to microbial growth in two phases. In this article, we first examine Monod’s thesis to demonstrate how and why Monod interpreted diauxie as a phenomenon of enzyme inhibition or suppression of adaptive enzymes. We also briefly investigate prior enzyme suppression studies, before Monod’s work, which indicate that he is the first person to observe diauxic growth. Second, we analyse Monod’s post-thesis publications throughout his scientific career, revealing that diauxic inhibition was a significant part of Monod’s scientific activities and greatly fascinated Monod until the end of his life. Paradoxically, Monod’s work and interest on diauxic inhibition are still neglected in historical recounts, focused mostly on Monod’s enzymatic adaptation studies. Indeed, we uncovered a statement by Monod’s colleague, Lwoff, who transformed a quotation from Monod by replacing the word phenomenon with enzymatic adaptation, which we believe has influenced historians. Finally, we offer hypotheses to explain why Lwoff altered Monod’s statement.
Highlights
On October 15, 1965, Jacques Monod, François Jacob, and André Lwoff, three biologists comprising a research team at the Pasteur Institute in Paris, received the Nobel Prize in Physiology or Medicine for their discoveries concerning genetic control of enzyme and virus synthesis
In 1945, Monod carried out experiments to test his competitive sugar usage model of the common precursor, in which he varied the ratio of the concentrations of sugars A "constitutive" and B "adaptive." The results showed that the level of diauxic inhibition can be reduced and even eliminated by increasing the concentration of the B sugar relative to the A sugar
By the end of the 1940s, both enzymatic adaptation and diauxic inhibition were studied by Monod in the context of his common precursor model in order to understand the fundamental question of enzyme formation
Summary
Based on his experimental results Monod demonstrated that diauxie is caused by the inhibitory action of certain sugars, such as glucose, on adaptive enzymes (meaning an enzyme that appears only in presence of its substrate). During the 1940s, Monod performed new experiments on diauxie and proposed a model of enzyme formation that explained the diauxic inhibition/suppression mechanism.
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