The catalase activity of ferrihaems

Abstract

1. The variation of the specific stoicheiometric catalatic activity of proto- and deuteroferrihaem with total ferrihaem concentration has been studied at 25 degrees C over a wide range of pH. For deuteroferrihaem the results imply that only monomeric ferrihaem species contribute significantly to the catalatic activity. Protoferrihaem is more highly dimerized in solution and, in this system, contributions to the catalatic activity from both monomeric and dimeric ferrihaem species were observed. The ratio of the specific activity of protoferrihaem monomer to that of dimer varied from approximately 20 at pH7 to 5x10(4) at pH12.2. 2. The specific activity of protoferrihaem monomer closely resembles that of deuteroferrihaem monomer, both in magnitude and pH-dependence. In both cases the activity is inversely proportional to [H(+)]. In contrast, the activity of catalase is independent of pH in the range 5-10. At pH13 the activity of ferrihaem monomer becomes equal to the maximal activity of catalase. The results are in good agreement with those reported by Brown et al. (1970b) and provide support for the assumptions upon which this previous analysis relied. 3. Information from the literature concerning the catalatic activity and dimerization of the iron(III) complex of 4,4',4'',4'''-tetrasulphophthalocyanine (Waldmeier & Sigel, 1971; Sigel et al., 1971) have been re-analysed. The results imply that both the monomeric and dimeric complexes contribute to catalatic activity and these activities closely resemble those of the corresponding protoferrihaem species.

Interactions of Porphyromonas gingivalis with oxyhaemoglobin and deoxyhaemoglobin

“…Whereas this enzyme is instrumental in protecting the cell during exposure to atmospheric oxygen and from macrophage-derived oxidants [31,32], it is likely that superoxide dismutase is an essential pre-requisite for haem acquisition from oxyhaemoglobin. Any H # O # generated by P. gingi alis through O − # dismutation would be destroyed by both monomeric and µ-oxo dimeric Fe(III)PPIX molecules by virtue of their inherent catalase activities [33].…”

Transmissible Burkholderia cepacia genomovar IIIa strains bind and convert monomeric iron(III) protoporphyrin IX into the μ-oxo oligomeric form

“…We have suggested that this protein may serve as a receptor for uptake of iron(III) protoporphyrin IX. Alternatively, it may facilitate cell-surface deposition of ferrihaems which can then act defensively against attack by hydrogen peroxide by virtue of their inherent catalase activity (Brown et al, 1970;Jones et al, 1973) as recently demonstrated for Porphyromonas gingivalis (Smalley et al, 2000). However, we have found that the ability of cells to bind iron(III) protoporphyrin IX is not restricted to HBP-positive genomovar IIIa isolates (Smalley et al, 2001).…”

“…In addition, the catalase activities of cells of both genomovar IIIa and I strains after exposure to iron(III) protoporphyrin IX monomers were double those of cells carrying bound m-oxo oligomers. This finding is predictable on the basis that the catalase activity of the monomer is higher than the m-oxo oligomer (Jones et al, 1973;Brown et al, 1970). The increased catalase activity displayed by the genomovar IIIa isolates as a result of binding of ferrihaems would provide an advantage over other genomovars to endure fluxes of H 2 O 2 released from neutrophils.…”

“…Thus, the fact that 77 and 149 kDa proteins were stained at 6?5 and not at 7?5 indicated that these components preferentially pick up monomers rather than m-oxo oligomers. Since Fe(III)PPIX.OH monomers are more catalytic than the m-oxo oligomers in their ability to destroy hydrogen peroxide (Brown et al, 1970;Jones et al, 1973), it is likely that Fe(III)PPIX.OH molecules bound to the cell surface at pH 6?5 would more efficiently protect against H 2 O 2 than m-oxo oligomers. However, it should be noted that the m-oxo oligomer (Brown et al, 1970) may be preferentially oxidized and partially decomposed compared to the monomer during exposure to H 2 O 2 (Grinberg et al, 1999) and thus constitute a cell-surface layer which can act as a sacrificial barrier against this oxidant as reported for P. gingivalis (Smalley et al, 2000).…”

“…However, ferrihaem molecules, i.e. the [Fe(III)PPIX] 2 O complex and Fe(III)PPIX.OH monomers, can destroy hydrogen peroxide by virtue of their inherent catalase activity (Brown et al, 1970;Jones et al, 1973) (Smalley et al, 2000). Haem-containing and carrying molecules, including haemoglobin, haemopexin (Barnard et al, 1993;Liem et al, 1975) and myeloperoxidase released from neutrophils represent a source of haem in the infected CF lung during inflammation.…”