Dec 4, 2003

The active site and mechanism of action of recombinant acetohydroxy acid synthase from tobacco

FEBS Letters
Moon-Young YoonJung-Do Choi


Acetohydroxy acid synthase (AHAS) is one of several enzymes that require thiamine diphosphate and a divalent cation as essential cofactors. Recently, the three-dimensional structure of the enzyme from yeast has been determined [Pang et al., J. Mol. Biol. 317 (2002) 249-262]. While this structure sheds light on the binding of the cofactors and the reaction mechanism, the interactions between the substrates and the enzyme remain unclear. We have studied the pH dependence of kinetic parameters in order to obtain information about the chemical mechanism in the active site. Data are consistent with a mechanism in which substrate selectively catalyzed to the enzyme with an unprotonated base having a pK of 6.48, and a protonated group having a pK of 8.25 for catalysis. The temperature dependence of kinetic parameters was pH-dependent, and the enthalpies of ionization, DeltaH(ion), calculated from the slope of pK(1) and pK(2) are both pH-independent. The solvent perturbation of kinetic parameters was pH-dependent, and the pK(1) from the acidic side and the pK(2) from the basic side were shifted down 0.4 pH units and shifted up 0.6 units as water was replaced by 15% ethanol, respectively. The data are discussed in terms of the acid-base...Continue Reading

  • References19
  • Citations2


Mentioned in this Paper

Cations, Divalent
Ethanol Measurement
Enzymes, antithrombotic
Proteins, Recombinant DNA
Acetohydroxyacid Synthetase I
Mutagenesis, Site-Directed

Trending Feeds


Coronaviruses encompass a large family of viruses that cause the common cold as well as more serious diseases, such as the ongoing outbreak of coronavirus disease 2019 (COVID-19; formally known as 2019-nCoV). Coronaviruses can spread from animals to humans; symptoms include fever, cough, shortness of breath, and breathing difficulties; in more severe cases, infection can lead to death. This feed covers recent research on COVID-19.

Bone Marrow Neoplasms

Bone Marrow Neoplasms are cancers that occur in the bone marrow. Discover the latest research on Bone Marrow Neoplasms here.

IGA Glomerulonephritis

IgA glomerulonephritis is a chronic form of glomerulonephritis characterized by deposits of predominantly Iimmunoglobin A in the mesangial area. Discover the latest research on IgA glomerulonephritis here.

Cryogenic Electron Microscopy

Cryogenic electron microscopy (Cryo-EM) allows the determination of biological macromolecules and their assemblies at a near-atomic resolution. Here is the latest research.

STING Receptor Agonists

Stimulator of IFN genes (STING) are a group of transmembrane proteins that are involved in the induction of type I interferon that is important in the innate immune response. The stimulation of STING has been an active area of research in the treatment of cancer and infectious diseases. Here is the latest research on STING receptor agonists.

LRRK2 & Immunity During Infection

Mutations in the LRRK2 gene are a risk-factor for developing Parkinson’s disease. However, LRRK2 has been shown to function as a central regulator of vesicular trafficking, infection, immunity, and inflammation. Here is the latest research on the role of this kinase on immunity during infection.

Antiphospholipid Syndrome

Antiphospholipid syndrome or antiphospholipid antibody syndrome (APS or APLS), is an autoimmune, hypercoagulable state caused by the presence of antibodies directed against phospholipids.

Meningococcal Myelitis

Meningococcal myelitis is characterized by inflammation and myelin damage to the meninges and spinal cord. Discover the latest research on meningococcal myelitis here.

Alzheimer's Disease: MS4A

Variants within membrane-spanning 4-domains subfamily A (MS4A) gene cluster have recently been implicated in Alzheimer's disease by recent genome-wide association studies. Here is the latest research.