Channeling behavior and activity models for Escherichia coli K-12 acetohydroxy acid synthases at physiological substrate levels.
The channeling behavior of acetohydroxy acid synthases I and III (EC 4.1.3.18; AHAS) was studied by computer simulation of activities over a wide range of concentrations for the substrates pyruvate and 2-ketobutyrate. The ratios of reaction rates for both channels and three-dimensional plots of single-channel reaction rates versus substrate concentrations were introduced to compare the substrate channeling properties of the isozymes. Substrate ranges were identified in which AHAS I and III operated both channels, and in which they used only one. Kinetic constants were varied to simulate whether and how AHAS might be made channel-specific. Our study suggests that AHAS might be made channel-specific for acetolactate but not for acetohydroxybutyrate. We postulate specific physiological roles for AHAS I and III to support cell growth under conditions that vary the levels and balance of substrates.
Herring
P A
PA
Department of Microbiology, Michigan State University, East Lansing 48824.
McKnight
B L
BL
Jackson
J H
JH
D000095:Acetolactate Synthase / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D002087:Butyrates / Q000378:metabolism; D003198:Computer Simulation; D004926:Escherichia coli / Q000201:enzymology* / Q000254:growth & development; D007527:Isoenzymes / Q000378:metabolism; D007532:Isoleucine / Q000378:metabolism; D007700:Kinetics; D011773:Pyruvates / Q000378:metabolism; D014633:Valine / Q000378:metabolism
D000596:Amino Acids; D002087:Butyrates; D007527:Isoenzymes; D011773:Pyruvates; D007532:Isoleucine; C005087:alpha-ketobutyric acid; D000095:Acetolactate Synthase; D014633:Valine