Thermal denaturation of glutathione reductase from cyanobacterium Spirulina maxima.
The thermal unfolding of glutathione reductase (NAD[P]H:GSSG oxidoreductase EC 1.6.4.2.) from cyanobacterium Spirulina maxima was monitored by differential scanning calorimetry and circular dichroism at neutral pH. Covalent cross-linking of enzyme at different temperatures revealed dimer as the species undergoing the thermal transition. A single endotherm was observed, but its thermodynamic parameters showed dependence on the scan rate. In the transition zone, aggregation of the dimeric species was observed. Analysis of the enzyme heated at 80 degrees C revealed that the resultant species retained a high content of secondary structure. The addition of low concentrations of guanidinium hydrochloride resulted in a full cooperative thermal transition. A model in which the dimeric protein undergoes a partial unfolding in a kinetically controlled fashion is proposed, such that the experimental value of delta H(cal) results from the simultaneous occurrence of endothermic and exothermic events.
Rojo-Domínguez
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A
Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, México, D.F., México.
Hernández-Arana
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A
Mendoza-Hernández
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G
Rendón
J L
JL
D001426:Bacterial Proteins / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D019281:Dimerization; D005980:Glutathione Reductase / Q000737:chemistry*; D019791:Guanidine; D006146:Guanidines / Q000494:pharmacology; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D010940:Plant Proteins / Q000737:chemistry*; D011489:Protein Denaturation; D053545:Spirulina
D001426:Bacterial Proteins; D006146:Guanidines; D010940:Plant Proteins; D005980:Glutathione Reductase; D019791:Guanidine