Acetohydroxyacid synthase isozyme I from Escherichia coli has unique catalytic and regulatory properties.
AHAS I is an isozyme of acetohydroxyacid synthase which is apparently unique to enterobacteria. It has been known for over 20 years that it has many properties which are quite different from those of the other two enterobacterial AHASs isozymes, as well as from those of "typical" AHASs which are single enzymes in a given organism. These include a unique mechanism for regulation of expression and the absence of a preference for forming acetohydroxybutyrate. We have cloned the two subunits, ilvB and ilvN, of this Escherichia coli isoenzyme and examined the enzymatic properties of the purified holoenzyme and the enzyme reconstituted from purified subunits. Unlike other AHASs, AHAS I demonstrates cooperative feedback inhibition by valine, and the kinetics fit closely to an exclusive binding model. The formation of acetolactate by AHAS I is readily reversible and acetolactate can act as substrate for alternative AHAS I-catalyzed reactions.
Vinogradov
Valerie
V
Department of Life Sciences, Ben-Gurion University of the Negev, POB 657, Beer-Sheva 84105, Israel.
Vyazmensky
Maria
M
Engel
Stanislav
S
Belenky
Inna
I
Kaplun
Alexander
A
Kryukov
Olga
O
Barak
Ze'ev
Z
Chipman
David M
DM
D000095:Acetolactate Synthase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D000096:Acetone / Q000031:analogs & derivatives / Q000378:metabolism; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins / Q000378:metabolism*; D025461:Feedback, Physiological; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D007536:Isomerism; D007700:Kinetics; D014633:Valine / Q000494:pharmacology
D029968:Escherichia coli Proteins; D007527:Isoenzymes; D000096:Acetone; C035293:1-hydroxy-1-phenyl-2-propanone; D000095:Acetolactate Synthase; C510092:IlvB protein, E coli; C510093:IlvN protein, E coli; D014633:Valine