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Slow Ca 2+ ‐induced inactive/active transition of the energy‐dependent Ca 2+ transporting system of rat liver mitochondria: clue for Ca 2+ influx cooperativity
Author(s) -
Kasparinsky F.O.,
Vinogradov A.D.
Publication year - 1996
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(96)00606-0
Subject(s) - cooperativity , mitochondrion , chemistry , biophysics , kinetics , activation energy , calcium , substrate (aquarium) , biochemistry , biology , physics , organic chemistry , quantum mechanics , ecology
Rat liver mitochondria essentially free of endogenous Ca 2+ show low initial rate of energy‐dependent Ca 2+ uptake. Preincubation of mitochondria under de‐energized conditions in the presence of small amounts of external Ca 2+ results in a 8–10‐fold time‐dependent increase of energy‐dependent Ca 2+ uptake. Ca 2+ ‐dependent activation of the Ca 2+ ‐transporting system follows first‐order kinetics ( in the presence of 5 μM Ca 2+ at 20°C). Ca 2+ ‐activated mitochondria demonstrate a simple hyperbolic initial rate‐Ca 2+ concentration dependence, whereas strong apparent cooperativity is observed in the velocity‐substrate curves for Ca 2+ ‐depleted mitochondria. It is concluded that apparent cooperativity of the energy‐dependent Ca 2+ uptake is due to slow (as compared with the ‘turnover number’) activation of a Ca 2+ ‐specific uniporter which is inactive in the absence of external Ca 2+ .