Regulation of yeast acetohydroxyacid synthase by valine and ATP

Pang, S. S. and Duggleby, R. G. (2001) Regulation of yeast acetohydroxyacid synthase by valine and ATP. Biochemical Journal, 357 3: 749-757. doi:10.1042/0264-6021:3570749

Author Pang, S. S.
Duggleby, R. G.
Title Regulation of yeast acetohydroxyacid synthase by valine and ATP
Journal name Biochemical Journal   Check publisher's open access policy
ISSN 0264-6021
Publication date 2001-08
Sub-type Article (original research)
DOI 10.1042/0264-6021:3570749
Volume 357
Issue 3
Start page 749
End page 757
Total pages 9
Place of publication London
Publisher Portland Press
Collection year 2001
Language eng
Subject C1
270108 Enzymes
780105 Biological sciences
0601 Biochemistry and Cell Biology
1101 Medical Biochemistry and Metabolomics
Abstract The first step in the common pathway for the biosynthesis of branched-chain amino acids is catalysed by acetohydroxyacid synthase (AHAS; EC The enzyme is found in plants, fungi and bacteria, and is regulated by controls on transcription and translation, and by allosteric modulation of catalytic activity. It has long been known that the bacterial enzyme is composed of two types of subunit, and a similar arrangement has been found recently for the yeast and plant enzymes. One type of subunit contains the catalytic machinery, whereas the other has a regulatory function. Previously, we have shown [Pang and Duggleby (1999) Biochemistry 38, 5222-5231] that yeast AHAS can be reconstituted from its separately purified subunits. The, reconstituted enzyme is inhibited by valine, and ATP reverses this inhibition. In the present work, we further characterize the structure and the regulatory properties of reconstituted yeast AHAS. High phosphate concentrations are required for reconstitution and it is shown that these conditions are necessary for physical association between the catalytic and regulatory subunits. It is demonstrated by CD spectral changes that ATP binds to the regulatory subunit alone, most probably as MgATP. Neither valine nor MgATP causes dissociation of the regulatory subunit from the catalytic subunit. The specificity of valine inhibition and MgATP activation are examined and it is found that the only effective analogue of either regulator of those tested is the non-hydrolysable ATP mimic, adenosine 5 '-[beta,gamma -imido]triphosphate. The kinetics of regulation are studied in detail and it is shown that the activation by MgATP depends on the valine concentration in a complex manner that is consistent with a proposed quantitative model.
Keyword Biochemistry & Molecular Biology
Acetolactate Synthase
Branched-chain Amino Acids
Kinetic Model
Subunit Interactions
Flavin Adenine-dinucleotide
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Medicine Publications
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Created: Tue, 14 Aug 2007, 15:18:37 EST