title: Reconstitution of holotransketolase is by a thiamin-diphosphate-magnesium complex.
abstract: When human erythrocyte apo-transketolase is mixed with cofactors and substrates, the progress curve exhibits a lag phase. Elimination of the lag phase requires the presence of saturating concentrations of cofactors, thiamin diphosphate and Mg2+. The most simple explanation of the observed hysteretic transition is that the slow binding of a Mg(2+)-thiamin-diphosphate species precedes slow isomerisation of the enzyme to the active form. Although the hysteretic transition involves more than one process, it does not involve the dissociation-association of enzyme subunits. The best estimate of the apparent Km, 1.59 +/- 0.23 microM, for the binding of Mg(2+)-thiamin diphosphate to transketolase was obtained in the presence of a high non-inhibitory concentration of magnesium and varied concentrations of thiamin diphosphate. Thus the reconstitution of the human enzyme differs from the yeast enzyme, which undergoes a rate-limiting dimerisation during reconstitution.
authors.affiliation: Department of Biochemistry, University of Queensland, Australia.
authors.forename: C K
authors.initials: CK
authors.lastname: Booth
authors.forename: P F
authors.initials: PF
authors.lastname: Nixon
mesh_terms: D004789:Enzyme Activation; D004912:Erythrocytes / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry*; D013379:Substrate Specificity; D013835:Thiamine Pyrophosphate / Q000737:chemistry* / Q000378:metabolism; D014174:Transketolase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D014174:Transketolase; D008274:Magnesium; D013835:Thiamine Pyrophosphate