A step towards understanding the folding mechanism of horseradish peroxidase. Tryptophan fluorescence and circular dichroism equilibrium studies.


Abstract

The guanidinium chloride denaturation/renaturation of the holo- and apo-horseradish peroxidase isoenzyme c (HRP) has been studied by fluorescence and circular dichroism spectroscopies. A distinct equilibrium intermediate of the apoprotein could be detected at low concentrations of guanidinium chloride (0.5 M). This intermediate has a secondary structure content like that of the native protein but a poorly defined tertiary structure. Renaturation of the apo-HRP is reversible and 100% activity could be obtained after addition of a twofold excess of free haem. The denaturation of the holo-HRP is more complex and occurs in two distinct steps; unfolding of the protein backbone and loss of the haem. The denatured protein folds back to its native conformation but the incorporation of the haem occurs only after the secondary structure is formed. Ca2+ appears to be important for the stability of the protein as the apo-HRP is more resistant to denaturation in the presence of Ca2+. The free-energy change during unfolding of the apo-HRP was determined in the absence and presence of Ca2+ and found to be 9.2 kJ/mol and 16.7 kJ/mol, respectively. The importance of Ca2+ to the protein stability was also supported by studies on the loss of the haem from the protoporphyrin-IX-apo-HRP complex. Study holds ProTherm entries: 7575, 7576 Extra Details: equilibrium intermediate; secondary structure content;,native conformation; protoporphyrin-IX-apo-HRP complex

Submission Details

ID: rfYL5BvX3

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:34 p.m.

Version: 1

Publication Details
Pappa HS;Cass AE,Eur. J. Biochem. (1993) A step towards understanding the folding mechanism of horseradish peroxidase. Tryptophan fluorescence and circular dichroism equilibrium studies. PMID:8444158
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