Author(s): Akerman KE, Wikstrm MK, Saris NE
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Abstract The kinetic plot (initial rate of Ca2+ transport versus concentration) of mitochondrial Ca2+ transport is hyperbolic in a sucrose medium. The plot becomes sigmoidal in the presence of competitive inhibitors of Ca2+ binding to low affinity sites of the membrane surface such as Mg2+ and K+. The plot also becomes sigmoidal in the presence of Ba2+. Ba2+ is a competitive inhibitor of both Ca2+ transport and Ca2+ binding to the low affinity sites. The 5i for the inhibition of Ca2+ transport by Ba2+ increases in the presence of K+ and Mg2+, which suggests a competition for the low affinity sites between the cations. The plot is still hyperbolic in the presence of La3+, which inhibits Ca2+ transport competitively. Ruthenium red which is a pure non-competitive inhibitor of mitochondrial Ca2+ transport, does not affect the shape of the kinetic plot. These results indicate that the surface potential, which depends on the ions bound to the low affinity sites, determines whether the kinetics of Ca2+ uptake in mitochondria is sigmoidal or hyperbolic.
This article was published in Biochim Biophys Acta
and referenced in Biochemistry & Analytical Biochemistry