Ca(2+) modulates respiratory and steroidogenic activities of human term placental mitochondria |
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Authors: | García-Pérez Cecilia Pardo Juan Pablo Martínez Federico |
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Affiliation: | Departamento de Bioqui;mica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, DF 04510, México, Mexico. |
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Abstract: | We investigated the effects of calcium on the oxidative metabolism and steroidogenic activity of human term placental mitochondria. Submicromolar Ca(2+) concentrations stimulated state 3 oxygen consumption with 2-oxoglutarate and isocitrate and activated the 2-oxoglutarate and the NAD-isocitrate dehydrogenases by diminishing their Michaelis-Menten constants. Ca(2+) inhibited NADP-isocitrate dehydrogenase (NADP-ICDH) and the synthesis of progesterone. The NADP-ICDH maximal velocity was threefold higher than that of NAD-ICDH and had a threefold lower K(m) for isocitrate than NAD-ICDH. Isocitrate but not malate or 2-oxoglutarate supported progesterone synthesis. Calcium inhibition of progesterone synthesis was observed with isocitrate but not with malate or 2-oxoglutarate. Tight regulation of NADP-isocitrate dehydrogenase by calcium ions suggests that this enzyme plays an important role in placental mitochondrial metabolism. |
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Keywords: | Mitochondria Steroidogenesis Placenta Respiration NADP-isocitrate dehydrogenase Calcium |
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