Purification and characterization of ferro- and cobalto-chelatases

A continuous anaerobic fluorimetric assay for ferrochelatase by monitoring porphyrin disappearance

A continuous spectrofluorimetric assay for determining ferrochelatase activity has been developed using the physiological substrates ferrous iron and protoporphyrin IX under strictly anaerobic conditions. In contrast to heme, the product of the ferrochelatase-catalyzed reaction, protoporphyrin IX is fluorescent, and therefore the progress of the reaction can be monitored by following the decrease in protoporphyrin fluorescence intensity (with excitation and emission wavelengths at 505 and 635 nm, respectively). This continuous fluorimetric assay detects activities as low as 0.01 nmol porphyrin consumed min(-1), representing an increase in sensitivity of up to two orders of magnitude over the currently used, discontinuous assays. The determination of the steady-state kinetic parameters of ferrochelatase yielded K(m)(PPIX)=1.4+/-0.2 microM, K(m)(Fe(2+))=1.9+/-0.3 microM, and k(cat)=4.0+/-0.3 min(-1). In addition to its applicability for acquisition of kinetic data to characterize ferrochelatase and recombinant variants, this new method should permit detection of low concentrations of ferrochelatase in biological samples.

Cloning of murine ferrochelatase

Ferrochelatase (protoheme ferro-lyase, EC 4.99.1.1) catalyzes the last step in the heme biosynthetic pathway, the chelation of ferrous iron and protoporphyrin to form heme. The activity of ferrochelatase is deficient in the inherited disease protoporphyria. In this study, murine ferrochelatase cDNAs were obtained by screening cDNA libraries with an oligonucleotide probe. The derived amino acid sequence of murine ferrochelatase has 47% identity with the recently cloned Saccharomyces cerevisiae ferrochelatase, but it is not significantly similar to other published sequences. Results of Southern blotting are consistent with a single murine ferrochelatase gene, while Northern blotting demonstrates two ferrochelatase transcripts in all tissues examined. The ferrochelatase protein and mRNAs have different relative concentrations in different tissues. The cloning of murine ferrochelatase cDNAs provides the basis for future studies on ferrochelatase gene expression and on the identification of the molecular defect in protoporphyria.

Liver ferrochelatase from normal and hexachlorobenzene porphyric rats. Mechanism of drug action

1. The action of hexachlorobenzene (HCB) on hepatic ferrochelatase was investigated. 2. A direct action of HCB, pentachlorophenol, porphyrins and haem on this enzyme activity was discarded. 3. In HCB porphyric liver there is probably an activator tightly bound to the enzyme. 4. Pyridoxal phosphate (PPL) may be a cofactor of ferrochelatase from both normal and porphyric rats. 5. The PPL would be involved in the binding site of Fe2+ or at least in the approaching of Fe2+ to the active site of the enzyme. 6. The differences found between normal and porphyric preparations could be attributed to conformational changes elicited by the HCB.