Affinity of Microsomal glutathione transferase 1 trimer to GSH once GSH on one binding site is deprotonated

Value 2.5 mM Range: ±0.5 mM
Organism Rat Rattus norvegicus
Reference Alander et al., Microsomal glutathione transferase 1 exhibits one-third-of-the-sites-reactivity towards glutathione. Arch Biochem Biophys. 2009 Jul 1 487(1):42-8. p. 46 left column, top sentencePubMed ID19416719
Method The pre-steady state kinetic properties of MGST1 [refs 20,21 in article] allows the performance of single turn-over experiments where the enzyme, equilibrated with various concentrations of GSH, is rapidly mixed with a stoichiometric (1/trimer) concentration of CDNB. Upon mixing a rapid burst of product formation and release takes place. Subsequent GSH rebinding to the empty site and slow thiolate anion formation can then be observed (the rebinding phase is shown in Fig. 5A). Fitting the GSH dependence of kobs for the thiolate anion formation (Fig. 5B and Eqs. (2) and (3)) yielded the Kd for GSH (2.5±0.5mM). The presence of a low affinity site for GSH is consistent with the mass spectrometry and structural data, and was outside the sensitivity range for detection by conventional equilibrium binding techniques.
Comments To summarise, GSH initially binds to each of the three low affinity sites in MGST1 (Kd=50 mM). Once one molecule of bound GSH is deprotonated (Kd=20µM), the remaining active sites bind their GSH more strongly (Kd=2.5mM for the third GSH), but cannot promote deprotonation. This results in one-third-of-sites reactivity. See BNID 105544, 105545, 105547
Entered by Uri M
ID 105546