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Equilibrium Unfolding Mechanism of Chicken Muscle Triose Phosphate Isomerase

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Triose phosphate isomerase (TIM) was prepared and purified from chicken breast muscle. The equilibrium unfolding of TIM by urea was investigated by following the changes of intrinsic fluorescence and circular dichroism spectroscopy, and the equilibrium thermal unfolding by differential scanning calorimetry (DSC). Results show that the unfolding of TIM in urea is highly cooperative and no folding intermediate was detected in the experimental conditions used. The thermodynamic parameters of TIM during its urea induced unfolding were calculated as ΔG =3.54 kcal•mol-1, and mG = 0.67 kcal•mol-1•M-1, which just reflect the unfolding of dissociated folded monomer to fully unfolded monomer transition, while the dissociation energy of folded dimer to folded monomer is probe silence. DSC results indicate that TIM unfolding follows an irreversible two-state step with a slow aggregation process. The cooperative unfolding ratio, ΔHcal/ΔHvH, was measured close to 2, indicating that the two subunits of chicken muscle TIM unfold independently. The van't Hoff enthalpy, ΔHvH, was estimated as about 200 kcal•mol-1. These results support the unfolding mechanism with a folded monomer formation before its tertiary structure and secondary structure unfolding.

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Keywords: CD; Chicken muscle triose phosphate isomerase; DSC; equilibrium unfolding mechanism; fluorescence; urea

Document Type: Research Article

Publication date: 2008-05-01

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  • Protein & Peptide Letters publishes short papers in all important aspects of protein and peptide research, including structural studies, recombinant expression, function, synthesis, enzymology, immunology, molecular modeling, drug design etc. Manuscripts must have a significant element of novelty, timeliness and urgency that merit rapid publication. Reports of crystallisation, and preliminary structure determinations of biologically important proteins are acceptable. Purely theoretical papers are also acceptable provided they provide new insight into the principles of protein/peptide structure and function.
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