HAEM SYNTHASE AND COBALT PORPHYRIN SYNTHASE IN VARIOUS MICRO-ORGANISMS

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Abstract
The preparation of a crude extract of Clostridium tetanomorphum containing cobalt prrphyrin synthase but little haem-synthase activity is described. The properties of cobalt porphyrin synthase in the clostridial extracts is compared with the properties of a haem synthase present in crude extracts of the yeast Torulopsis utilis. Cobalt porphyrin synthase in extracts of C. tetanomorphum inserts Co2+ ions into the following dicarboxylic porphyrins in descending order of rate of insertion meso-, deutero- and proto-porphyrins. Esterification renders meso- and deutero-porphyrins inactive as substrates. Neither the tetracarboxylic (coproporphyrin-III) nor the octacarboxylic (uroporphyrin-III) compounds are converted into cobalt prophyrins by the extract, but the non-enzymic incorporation of Co2+ ions into these two porphyrins is rapid. These extracts are unable to insert Mn2+, Zn2+, Mg2+, or Cu2+ ions into mesoporphyrin. Crude extracts of T. utilis readily insert both Co2+ and Fe2+ ions into deutero-, meso, and proto-porphyrins. Unlike the extracts of C. tetanomorphum, these preparations catalyze the insertion of Co2+ ions into deuteroporphyrin more rapidly than into mesoporphyrin. This parallels the formation of haems by the T. utilis extract. Cobalt porphyrin synthase is present in the particulate fraction of the extracts of C. tetanomorphum but requires a heat-stable factor present in the soluble fraction. This soluble factor can be replaced by reduced glutathione (GSH). Cobalt porphyrin synthase in the clostridial extract is inhibited by iodoacetamide and to a smaller extent by p-chloromecuribenzoate and N-ethylmaleimide. The haem synthases of T. utilis and Micrococcus denitrificans are also inhibited by various thiol reagents.