title: Economics of membrane occupancy and respiro-fermentation.
abstract: The simultaneous utilization of efficient respiration and inefficient fermentation even in the presence of abundant oxygen is a puzzling phenomenon commonly observed in bacteria, yeasts, and cancer cells. Despite extensive research, the biochemical basis for this phenomenon remains obscure. We hypothesize that the outcome of a competition for membrane space between glucose transporters and respiratory chain (which we refer to as economics of membrane occupancy) proteins influences respiration and fermentation. By incorporating a sole constraint based on this concept in the genome-scale metabolic model of Escherichia coli, we were able to simulate respiro-fermentation. Further analysis of the impact of this constraint revealed differential utilization of the cytochromes and faster glucose uptake under anaerobic conditions than under aerobic conditions. Based on these simulations, we propose that bacterial cells manage the composition of their cytoplasmic membrane to maintain optimal ATP production by switching between oxidative and substrate-level phosphorylation. These results suggest that the membrane occupancy constraint may be a fundamental governing constraint of cellular metabolism and physiology, and establishes a direct link between cell morphology and physiology.
authors.affiliation: Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Kai
authors.initials: K
authors.lastname: Zhuang
authors.forename: Goutham N
authors.initials: GN
authors.lastname: Vemuri
authors.forename: Radhakrishnan
authors.initials: R
authors.lastname: Mahadevan
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000332:Aerobiosis; D000693:Anaerobiosis; D002462:Cell Membrane / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000502:physiology*; D005285:Fermentation; D015964:Gene Expression Regulation, Bacterial; D055786:Gene Knockout Techniques; D005798:Genes, Bacterial; D005947:Glucose / Q000378:metabolism; D051246:Glucose Transport Proteins, Facilitative / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism*; D010766:Phosphorylation
chemical_list: D051246:Glucose Transport Proteins, Facilitative; D008565:Membrane Proteins; D000255:Adenosine Triphosphate; D003576:Electron Transport Complex IV; D005947:Glucose; D010100:Oxygen