The effect of calmodulin and far-red light on the kinetic properties of the mitochondrial and microsomal calcium-ion transport system from corn |
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Authors: | Peter Dieter Dieter Marmé |
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Affiliation: | 1. Institut für Biologie III der Universit?t, Sch?nzlestrasse 1, D-7800, Freiburg, Federal Republic of Germany
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Abstract: | The kinetic properties of active Ca2+ transport into mitochondria and microsomal membrane vesicles prepared from coleoptiles of dark-and light-grown corn seedlings have been studied. The apparent values for K m and V max for Ca2+ of the mitochondrial transport system from dark-grown plants are about one order of magnitude higher than those from the microsomal transport system. Calmodulin has no effect on the Ca2+ accumulation into mitochondria whereas the apparent maximum transport velocity and affinity for Ca2+ of the microsomal Ca2+-transport system are both increased by calmodulin. When intact corn seedlings are irradiated with far-red light, the calmodulin-induced increase of the apparent maximum transport velocity and affinity for Ca2+ can no longer be observed. From these data it can be concluded that the low cytoplasmic Ca2+ concentration in the cytoplasm of coleoptile cells from dark-grown corn is maintained by a calmodulin-regulated Ca2+ pump. Irradiation with photomorphogenically active far-red light lowers the Ca2+-transport activity and thus causes an increase of the cytoplasmic, free-Ca2+ concentration. The physiological implications will be discussed. |
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