| Co-Investigator(Kenkyū-buntansha) |
FURUKAWA Takako Kansai Medical University, Hygiene, Research Associate, 医学部, 助手 (00221557)
KOHNO Hirao Kansai Medical University, Hygiene, Assistant Professor., 医学部, 講師 (30148522)
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| Research Abstract |
Coproporphyrinogen oxidase (CPOX), protoporphyrinogen oxidase (PPOX) and ferrochelatase (FECH) in terminal steps of heme biosynthesis are located in mitochondria. To clarify association and interaction of three enzymes in mitochondria where transport of porphyrin intermediates occurs, regulation of expressions of cloned CPOX,PPOX and FECH during erythroid differentiation was examined. The induction of CPOX and FECH mRNAs in mouse erythroleukemia cells occurred within 6 h after dimethylsulfoxide treatment, while PPOX mRNA remained constant, indicating that PPOX is not a rate-limiting step of heme biosynthesis. Onset of an increase in heme content of the differentiated cells delayd at least 6h, as compared with the induction of FECH,suggesting that the rate limiting step of heme biosynthesis during erythroid differentiation cannot be ascribed for heme synthesis but iron metabolism in mitochondria. Attempts to isolate iron metabolizing molecules, however, have not been succeeded. Active CPOX of the mouse cloned cDNA was expressed as a soluble form, and histidine residues are essential to maintain the structure as well as to catalytic activity. Otherwise, C-terminus of human FECH contains iron-sulfur cluster which is destroyed by NO,leading to inactivation of the enzyme. Finally we also demonstrated that peripheral-type benzodiazepine receptors exhibit affinity for porphyrins and heme, and suggest that the receptors play a role of transport of porphyrins and heme in mitochondria.
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