PURIFICATION AND PROPERTIES OF A HALOPHILIC CATALASE PEROXIDASE FROM HALOARCULA-MARISMORTUI

A heme protein, hCP, from the extreme halophile, Haloarcula marismortu i, showing both peroxidatic and catalatic activity has been purified a nd characterized as a catalase-peroxidase. Catalatic activity is enhan ced by molar concentrations of NaCl or (NH4)(2)SO4, while peroxidase a ctivity decreases with increasing salt concentration. Optimal pH value s are 6.0 for peroxidatic activity assayed in absence of NaCl and 7.5 for catalatic activity assayed in molar concentrations of NaCl. The tw o activities present saturation behaviour with increasing H2O2 concent ration with apparent K-m values of 0.5 and 2.5 mM for the peroxidatic and catalatic activities, respectively. A molecular mass of 81292 +/- 9 Da was measured for the polypeptide by mass spectroscopy. One heme g roup (protoporphyrin IX with an iron atom in the ferric state) is asso ciated with one molecule of hCP. Its amino-acid composition shows hCP to contain a high proportion of acidic residues. The EPR spectrum of t he NO-compound of reduced (ferrous) hCP strongly suggests that the pro ximal ligand of the heme is the imidazole group of a histidine residue .