Slow Ca2+-induced inactive/active transition of the energy-dependent Ca2+ transporting system of rat liver mitochondria: clue for Ca2+ influx cooperativity.
Rat liver mitochondria essentially free of endogenous Ca2+ show low initial rate of energy-dependent Ca2+ uptake. Preincubation of mitochondria under de-energized conditions in the presence of small amounts of external Ca2+ results in a 8-10-fold time-dependent increase of energy-dependent Ca2+ uptake. Ca2+-dependent activation of the Ca2+-transporting system follows first-order kinetics (t1/2 approximately 1 min in the presence of 5 microM Ca2+ at 20 degrees C). Ca2+-activated mitochondria demonstrate a simple hyperbolic initial rate-Ca2+ concentration dependence, whereas strong apparent cooperativity is observed in the velocity-substrate curves for Ca2+-depleted mitochondria. It is concluded that apparent cooperativity of the energy-dependent Ca2+ uptake is due to slow (as compared with the 'turnover number') activation of a Ca2+-specific uniporter which is inactive in the absence of external Ca2+.
Kasparinsky
F O
FO
Department of Biochemistry, School of Biology, Moscow State University, Russian Federation.
Vinogradov
A D
AD
D000818:Animals; D001150:Arsenazo III / Q000494:pharmacology; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism*; D051381:Rats; D013386:Succinates / Q000378:metabolism; D019802:Succinic Acid
D015220:Calcium Channels; D008565:Membrane Proteins; D013386:Succinates; D001150:Arsenazo III; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D004533:Egtazic Acid; D019802:Succinic Acid; D002118:Calcium