tailieunhanh - Báo cáo khoa học: Allosteric modulation of Euphorbia peroxidase by nickel ions

A class III peroxidase, isolated and characterized from the latex of the perennial Mediterranean shrub Euphorbia characias, contains one ferric iron–protoporphyrin IX pentacoordinated with a histidine ‘proximal’ ligand as heme prosthetic group. | ỊFEBS Journal Allosteric modulation of Euphorbia peroxidase by nickel ions Francesca Pintus1 Anna Mura1 Andrea Bellelli2 Alessandro Arcovito3 Delia Spano1 Anna Pintus1 Giovanni Floris1 and Rosaria Medda1 1 Department of Applied Sciences in Biosystems University of Cagliari Cagliari Italy 2 Department of BiochemicalSciences A. Rossi Fanelli University of Rome La Sapienza and CNR Center of Molecular Biology Rome Italy 3 Institute of Biochemistry and ClinicalBiochemistry Catholic University of Sacred Heart Rome Italy Keywords calcium heme proteins hydrogen peroxide nickel peroxidase Correspondence R. Medda Dipartimento di Scienze Applicate ai Biosistemi CittỂỉ Universitaria I-09042 Monserrato CA Italy Fax 39 070 6754523 Tel 39 070 6754517 E-mail rmedda@ Received 13 November 2007 revised 7 January 2008 accepted 9 January 2008 doi A class III peroxidase isolated and characterized from the latex of the perennial Mediterranean shrub Euphorbia characias contains one ferric iron-protoporphyrin IX pentacoordinated with a histidine proximal ligand as heme prosthetic group. In addition the purified peroxidase contained 1 mole of endogenous Ca2 per mole of enzyme and in the presence of excess Ca2 the catalytic efficiency was enhanced by three orders of magnitude. The incubation of the native enzyme with Ni2 causes reversible inhibition whereas in the presence of excess Ca2 Ni2 leads to an increase of the catalytic activity of Euphorbia peroxidase. UV visible absorption spectra show that the heme iron remains in a quantum mechanically mixed-spin state as in the native enzyme after addition of Ni2 and only minor changes in the secondary or tertiary structure of the protein could be detected by fluorescence or CD measurements in the presence of Ni2 . In the presence of H2O2 and in the absence of a reducing agent Ni2 decreases the catalase-like activity of Euphorbia peroxidase and accelerates another pathway in which the inactive stable .