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Yeast mitochondrial calcium uptake: regulation by polyamines and magnesium ions
T V Votyakova1, E N Bazhenova, R A Zvjagilskaya
1A. N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow.
Abstract:
Spermine, spermidine, and magnesium ions modulate the kinetic parameters of the Ca2+ transport system of Endomyces magnusii mitochondria. Mg2+ at concentrations up to 5 mM partially inhibits Ca2+ transport with a half-maximal inhibiting concentration of approximately 0.5 mM. In the presence of 2 mM MgCl2, the S0.5 value of the Ca2+ transport system increases from 220 to 490 microM, which indicates decreased affinity for the system. Spermine and spermidine exert an activating effect, having half-maximal concentrations of 12 and 50 microM, respectively. In the case of spermine, the S0.5 value falls to 50-65 microM, which implies an increase in the transport system affinity for Ca2+. Both Mg2+ and spermine cause a decrease of the Hill coefficient, giving evidence for a smaller degree of cooperativity. Spermine and spermidine enable yeast mitochondria to remove Ca2+ from the media completely. In contrast, Mg2+ lowers the mitochondrial buffer capacity. When both Mg2+ and spermine are present in the medium, their effects on the S0.5 value and the free extramitochondrial Ca2+ concentration are additive. The ability of spermine and Mg2+ to regulate yeast mitochondrial Ca2+ transport is discussed.
Insights
Spermine, spermidine, and magnesium ions significantly impact calcium transport in yeast mitochondria. These molecules modulate affinity and cooperativity, influencing how mitochondria manage calcium levels.
Area of Science:
- Mitochondrial physiology
- Biochemistry
- Ion transport mechanisms
Background:
- Mitochondria play a crucial role in cellular calcium homeostasis.
- The Ca2+ transport system in Endomyces magnusii mitochondria is essential for regulating intracellular calcium levels.
- Polyamines like spermine and spermidine, along with magnesium ions, are known to interact with cellular processes.
Purpose of the Study:
- To investigate the modulatory effects of spermine, spermidine, and magnesium ions on the kinetic parameters of the Ca2+ transport system in Endomyces magnusii mitochondria.
- To elucidate the specific mechanisms by which these substances influence calcium uptake and buffering capacity.
- To understand the combined effects of magnesium and spermine on mitochondrial calcium transport.
Main Methods:
- Kinetic analysis of Ca2+ transport in isolated Endomyces magnusii mitochondria.
- Measurement of Ca2+ transport parameters (S0.5, Hill coefficient) under varying concentrations of Mg2+, spermine, and spermidine.
- Assessment of mitochondrial calcium buffering capacity in the presence of these ions.
Main Results:
- Magnesium ions (Mg2+) partially inhibit Ca2+ transport, decreasing affinity and lowering the Hill coefficient, indicating reduced cooperativity.
- Spermine and spermidine activate Ca2+ transport, increasing affinity for Ca2+ and decreasing the Hill coefficient.
- Spermine and spermidine enhance the ability of mitochondria to completely remove Ca2+ from the medium, while Mg2+ reduces mitochondrial buffer capacity.
Conclusions:
- Spermine, spermidine, and Mg2+ are significant modulators of yeast mitochondrial Ca2+ transport kinetics.
- These ions differentially affect Ca2+ affinity, cooperativity, and buffering capacity, highlighting their distinct roles in mitochondrial calcium regulation.
- The additive effects of Mg2+ and spermine suggest complex interactions in controlling extramitochondrial Ca2+ concentrations.