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Jones MS, Jones OT: Ferrochelatase of Rhodopseudomonas spheroides. Biochem J. 1970 Sep;119(3):453-62.
Extracts of Rhodopseudomonas spheroides contain two ferrochelatases: one is soluble and forms metalloporphyrins from deuteroporphyrin and haematoporphyrin; the other is particulate and forms metalloporphyrins from protoporphyrin, mesoporphyrin, deuteroporphyrin and haematoporphyrin. Neither enzyme incorporates Mg (2+) into porphyrins or Fe (2+) into porphyrin cytochrome c. By using the particulate enzyme, plots of 1/v versus 1/s when one substrate was varied and the other kept constant showed that neither substrate affected the K (m) of the other. The suggested sequential mechanism for the reaction is supported by derivative plots of slopes and intercepts. The K (m) for deuteroporphyrin was 21.3mum and that for Co (2+) was 6.13mum. The enzyme incorporated Co (2+), Fe (2+), Zn (2+), Ni (2+) and Mn (2+); Cd (2+) was not incorporated and was an inhibitor, competitive with respect to Co (2+), non-competitive with respect to deuteroporphyrin. The K (i) for Cd (2+) was 0.73mum. Ferrochelatase was inhibited by protohaem, non-competitively with respect to Co (2+) or with respect to deuteroporphyrin. Inhibition by magnesium protoporphyrin was non-competitive with respect to deuteroporphyrin, uncompetitive with respect to Co (2+). The inhibitory concentrations of the metalloporphyrins are lower than those required for the inhibition of delta-aminolaevulate synthetase by protohaem. Fe (2+) is not incorporated aerobically into porphyrins unless an electron donor, succinate or NADH, is supplied; the low aerobic rate of metalloporphyrin synthesis obtained is insensitive to rotenone and antimycin. The rate of Fe (3+) incorporation increases as anaerobic conditions are achieved. |
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