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The unfolding enthalpy of the pH 4 molten globule of apomyoglobin measured by isothermal titration calorimetry

Published online by Cambridge University Press:  01 July 2000

MARC JAMIN ,
MARIAN ANTALIK ,
STEWART N. LOH ,
D. WAYNE BOLEN  and
ROBERT L. BALDWIN
MARC JAMIN
Affiliation:
Department of Biochemistry, Beckman Center, Stanford University School of Medicine, Stanford, California 94305-5307 Present address: Laboratoire de Biophysique Moleculaire et Cellulaire DBMS/BMC CEA-Grenoble, 17, rue des Martyrs, Grenoble 38054, France.
MARIAN ANTALIK
Affiliation:
Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston, Texas 77555-1052 Present address: Department of Biophysics, Institute of Experimental Physics, Slovak Academy of Sciences, Kosice 04353, Slovakia.
STEWART N. LOH
Affiliation:
Department of Biochemistry, Beckman Center, Stanford University School of Medicine, Stanford, California 94305-5307 Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, New York 13210
D. WAYNE BOLEN
Affiliation:
Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston, Texas 77555-1052
ROBERT L. BALDWIN
Affiliation:
Department of Biochemistry, Beckman Center, Stanford University School of Medicine, Stanford, California 94305-5307
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Abstract

The unfolding enthalpy of the pH 4 molten globule from sperm whale apomyoglobin has been measured by isothermal titration calorimetry, using titration to acid pH. The unfolding enthalpy is close to zero at 20 °C, in contrast both to the positive values expected for peptide helices and the negative values reported for holomyoglobin and native apomyoglobin. At 20 °C, the hydrophobic interaction should make only a small contribution to the unfolding enthalpy according to the liquid hydrocarbon model. Our result indicates that some factor present in the unfolding enthalpies of native proteins makes the unfolding enthalpy of the pH 4 molten globule less positive than expected from data for peptide helices.

Keywords

apomyoglobinmolten globuletitration calorimetryunfolding enthalpy
Type
Research Article
Information
Protein Science , Volume 9 , Issue 7 , July 2000 , pp. 1340 - 1346
Copyright
2000 The Protein Society

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