Volume changes of the molten globule transitions of horse heart ferricytochrome c: a thermodynamic cycle.
Volume changes among the unfolded (U), native (N), and molten globule (MG) conformations of horse heart ferricytochrome c have been measured. U to N (pH 2 to pH 7) was determined in the absence of added salt to be -136 +/- 5 mL/mol protein. U to MG (pH 2, no added salt to pH 2, 0.5 M KCl) yielded + 100 +/- 6 mL/mol. MG to N was broken into two steps, N to NClx at pH 7 by addition of buffered KCl to buffered protein lacking added salt (NClx = N interacting with an unknown number, X, of chloride ions), and MG to NClx by jumping MG at pH 2 in 0.5 M KCl to pH7 at the same salt concentration. The delta V of N to NClx was -30.9 +/- 1.4 mL/mol protein, whereas MG to NClx entailed a delta V of -235 +/- 6 mL/mol. Within experimental error, the results add up to zero for a complete thermodynamic cycle. We believe this to be the first volumetric cycle to have been measured for the conformational transitions of a protein. The results are discussed in terms of hydration contributions from deprotonation of the protein, other hydration effects, and the formation and/or enlargement of packing defects in the protein's tertiary structure during the steps of folding.
Foygel
K
K
Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, New Jersey 08903, USA.
Spector
S
S
Chatterjee
S
S
Kahn
P C
PC
D000818:Animals; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003574:Cytochrome c Group / Q000737:chemistry*; D006736:Horses; D006863:Hydrogen-Ion Concentration; D009206:Myocardium / Q000737:chemistry; D011189:Potassium Chloride / Q000494:pharmacology; D011487:Protein Conformation; D017510:Protein Folding; D013816:Thermodynamics
D003574:Cytochrome c Group; D011189:Potassium Chloride