Abstract
1. 1. Ca 2+ in the culture medium stimulates only slightly the growth and respiration of Saccharomyces cerevisiae. 2. 2. Neither energy-linked Ca 2+ transport nor high-affinity Ca 2+ binding occur in mitochondria isolated from Saccharomyces cerevisiae or from Torulopsis utilis. 3. 3. Metabolism-independent, low-affinity binding of Ca 2+ does, however, occur in mitochondria isolated from both yeasts. The concentration of these sites varies between 40 and 50 nmoles per mg of mitochondrial protein. Their affinity for Ca 2+ is rather low ( K m = 10–20 μM). 4. 4. Mitochondria of Saccharomyces cerevisiae contain about 10 nmoles of endogenous Ca 2+ per mg of mitochondrial protein, which is bound or sequestered in a very stable manner. 5. 5. The respiration of mitochondria from Saccharomyces cerevisiae is stimulated by valinomycin in the presence of KCl, suggesting that energy-linked transport of K + occurs. 6. 6. The results show that energy-linked Ca 2+ transport is not a universal attribute of intact mitochondria from all species. Since the yeast cells lack high-affinity Ca 2+ binding capacity, they may lack a specific Ca 2+ carrier. The basic energy-dependent cation pump may however be present in these mitochondria, since they can transport K + in the presence of valinomycin.
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