ISSN:
0887-3585
Schlagwort(e):
allostery
;
hexameric insulin
;
positive and negative cooperativity
;
half-site reactivity
;
Chemistry
;
Biochemistry and Biotechnology
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Medizin
Notizen:
The insulin hexamer is an allosteric protein exhibiting both positive and negative cooperative homotropic interactions and positive cooperative heterotropic interactions (C. R. Bloom et al., J. Mol. Biol. 245, 324-330, 1995). In this study, detailed spectroscopic analyses of the UV/Vis absorbance spectra of the Co(II)-substituted human insulin hexamer and the 1H NMR spectra of the Zn(II)-substituted hexamer have been carried out under a variety of ligation conditions to test the applicability of the sequential (KNF) and the half-site reactivity (SMB) models for allostery. Through spectral decomposition of the characteristic d → d transitions of the octahedral Co(II)-T-state and tetrahedral Co(II)-R-state species, and analysis of the 1H NMR spectra of T- and R-state species, these studies establish the presence of preexisting T- and R-state protein conformations in the absence of ligands for the phenolic pockets. The demonstration of preexisting R-state species with unoccupied sites is incompatible with the principles upon which the KNF model is based. However, the SMB model requires preexisting T- and R-states. This feature, and the symmetry constraints of the SMB model make it appropriate for describing the allosteric properties of the insulin hexamer. Proteins 26:377-390 © 1996 Wiley-Liss, Inc.
Zusätzliches Material:
8 Ill.
Materialart:
Digitale Medien
