Studies on the ferrochelatase activity of mitochondria and submitochondrial particles with special refefence to the regulatory function of the mitochondrial inner membrane

Mitochondrial ferrochelatase activity has been studied in coupled rat liver mitochondria and in ultrasonically treated rat liver mitochondria using deuteroporphyrin IX and Fe(III) as the substrates. 1. 1. There were significant differences between the ferrochelatase reaction of intact mitochondria as compared to sonicated mitochondria with respect to pH and temperature optima, changes in substrate and protein concentration, and sensitivity to uncoupler and product inhibition. 2. 2. The translocation of iron and deuteroporphyrin to the ferrochelatase on the M-side of the inner membrane depended on an energized inner membrane, i.e. when the uncoupler carbonyl cyanide m-chlorophenylhydrazone was added to a suspension of intact mitochondria prior to either iron or deuteroporphyrin, the ferrochelatase reaction was depressed by approx. 70%. The uncoupler had no effect on the ferrochelatase reaction of sonicated mitochondria. 3. 3. Hemin inhibited the ferrochelatase reaction of intact mitochondria as well as of sonicated mitochondria, partly by inhibiting the catalytic activity of the ferrochelatase, and partly by interfering with the translocation of the substrate(s). 4. 4. When the mitochondria were incubated in a sucrose medium, endogenously synthesized deuteroheme did not penetrate freely to the outside of the inner membrane. 5. 5. It is concluded that the transport of the substrates as well as the products across the inner membrane serves an important regulatory role in the overall ferro-chelatase reaction.