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The charge transfer band in horseradish peroxidase correlates with heme in‐plane distortions induced by calcium removal
Author(s) -
Laberge Monique,
Szigeti Krisztian,
Fidy Judit
Publication year - 2004
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.20040
Subject(s) - chemistry , heme , horseradish peroxidase , calcium , peroxidase , crystallography , enzyme , photochemistry , biophysics , biochemistry , organic chemistry , biology
Horseradish peroxidase C (HRPC) is a class III peroxidase whose structure is stabilized by the presence of two endogenous calcium atoms. Calcium removal has been shown to decrease the enzymatic activity of the enzyme. The spin state of the iron, a mixture of high spin (HS) and mixed quantum spin state (QS) consisting of intermediate spin (IS) 3/2 + (HS) 5/2, is also significantly affected by calcium removal, going from a predominant QS component to a predominant HS component upon removal of one calcium. Removal of both calcium ions, however, results in the appearance of a significant LS contribution, easily monitored in the charge transfer (CT) band region by low‐T absorption. Normal structural decomposition (NSD) calculations of the in‐plane (ip) modes of the heme extracted from HRPC native and Ca 2+ ‐depleted models show that removal of the proximal calcium is associated with perturbed E u and increased A 1g ip distortions of the heme. The effect of complete or distal calcium removal on the heme also results in increased A 1g ip distortions, but in significantly decreased E u distortions. The overall effect is to decrease the nonplanarity of the heme: the total ip distortion of the native HRPC heme is 0.200 and 0.134 Å for the Ca 2+ ‐depleted species. Our NSD results corroborate the role proposed for the protein matrix, namely to fine‐tune the active site by inducing subtle changes in heme planarity and spin state of the iron. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004