Abstract
The interactions of Ca 2+ with mitochondria from Saccharomyces cerevisiae were explored. Mitochondria were loaded with the metallochromic dye Fluo-3 to measure the concentration of free calcium in the matrix. Addition of EGTA or Ca 2+ led to fluctuations in mitochondrial free calcium between 120 and 400 nM. Ca 2+ variations were slower at 4°C than at 25°C or in the presence of phosphate instead of acetate. The net uptake of 45Ca 2+ was higher with phosphate than with acetate. The optimum pH for Ca 2+ uptake was 6.8. Ruthenium red did not affect the uptake of Ca 2+. Addition of antimycin-A or uncouplers led to a small and transient release of Ca 2+. Addition of EGTA or the monovalent cations Na + or K + resulted in higher release of Ca 2+. Site I but not site II dependent O 2 consumption was partially inhibited by EGTA. The effect of Ca 2+ on NADH oxidation is similar to results reported with enzymes from mammalian sources which use NADH, such as the pyruvate, isocitrate and oxoglutarate dehydrogenases.
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