A calorimetric study of pH-dependent thermal unfolding of leghemoglobin a from soybean.
The purpose of the present work is to study the pH-dependent thermal denaturation of soybean leghemoglobin fraction a in a cyanide complex (Lba.CN) and to compare the results with those of myoglobin (Mb), apomyoglobin (apoMb) and cyanometmyoglobin (Mb.CN) as well. Comparing measured calorimetrically change of enthalpy (DeltaHcal) and calculated Van't Hoff change of enthalpy (DeltaHvh) we have found that heat denaturation of Lba.CN can be described by the two-state transition model. The average value of the change of heat capacity (DeltaCpd) of Lba.CN is between such values for apoMb and Mb.CN suggesting for some stabilisation role of the cyanide ion (CN-) on the protein molecule. The maximum change of Gibbs free energy (DeltaGmax) of Lba.CN is between 7.0 and 11.2 kcal/mol depending on pH. The heat-denaturation of the protein occurs on heating the protein solution above 25 degrees C while the cold-denaturation occurs on cooling the protein below 25 degrees C.
Tzoneva
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RD
Institute of Biophysics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 21, Sofia 1113, Bulgaria. rumitz@obzor.bio21.acad.bg
Mishonova-Alexova
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EI
D002152:Calorimetry, Differential Scanning; D006863:Hydrogen-Ion Concentration; D007874:Leghemoglobin / Q000737:chemistry*; D017510:Protein Folding; D013025:Glycine max / Q000737:chemistry*
D007874:Leghemoglobin