Ferrochelatase activity inAzospirillum brasilense with reference to the influence of metal cations

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Abstract
Ferrochelatase in membrane preparations fromAzospirillum brasilense displayed an activity of 2.17 μmol protoheme formed · h−1 · mg protein−1 which is 10-fold greater than previous reports for other bacteria. This ferrochelatase showed an apparentK m of 20.9 μM for Fe2+, a pH optimum of 6.0–6.5, and stimulation by oleic or stearic acids. Co2+, Cu2+ and Zn2+ inhibited the incorporation of Fe2+ into protoporphyrin IX while Ni2 and Mg2+ had no effect on protoheme synthesis. Activity with Fe2+ and mesoporphyrin IX was less than with protoporphyrin IX but deuteroporphyrin IX produced the highest rate of protoheme synthesis. The membrane fraction containing ferrochelatase activity was found to insert Cu2+, Ni2+, Zn2+ and Co2+ enzymatically into protoporphyrin IX to produce metalloporphyrins. Cu2+ incorporation into protoporphyrin IX proceeded at a rate greater than with Fe2+ and theK m for Cu2+ was 21.9 μM.