Properties of membrane bound ferrochelatase purified from baboon liver mitochondria

1. 1. Baboon ferrochelatase was purified to apparent homogeneity. 2. 2. The pH optimum was 7.85 and the pI 5.3. 3. 3. The estimated molecular weight was 205 K made up by two 50+60 K heterodimers. 4. 4. The K m, values for proto- and mesoporphyrin were 18.5 and 10.8 μM with iron as co-substrate. With cobalt as co-substrate the K m values were 34.5 and 10.4 μM, respectively. The mean K m value for iron was 2.2 μM while cobalt acted as a complete inhibitor. 5. 5. Lead played a dual role that of both pseudo substrate and inhibitor. As shown by inhibitor kinetics, Pb acted as a two-step two-site parabolic competitive inhibitor. The mean K i value at low Pb levels was 0.65 mM and at high levels 0.17 mM. 6. 6. Substrate inhibition occurred above 36 μM for proto- and 44 μM for mesoporphyrin with iron as co-substrate. For iron,with mesoporphyrin as co-substrate it occurred above 29 μM.