Calcium-binding properties of the mitochondrial channel-forming hydrophobic component.
A hydrophobic, low-molecular weight component extracted from mitochondria forms a Ca2+-activated ion channel in black-lipid membranes (Mironova et al., 1997). At pH 8.3-8.5, the component has a high-affinity binding site for Ca2+ with a Kd of 8 x 10(-6) M, while at pH 7.5 this Kd was decreased to 9 x 10(-5) M. Bmax for the Ca2+-binding site did not change significantly with pH. In the range studied, 0.2 +/- 0.06 mmol Ca2+/g component were bound or one calcium ion to eight molecules of the component. The Ca2+ binding was strongly decreased by 50-100 mM Na+, but not by K+. Treatment of mitochondria with CaCl2 prior to ethanolic extraction resulted in a high level of Ca2+-binding capacity of the partially purified component. Cyclosporin A, a specific inhibitor of the mitochondrial permeability transition, when added to the mitochondrial suspension, decreased the Ca2+-binding activity of the purified extract severalfold. The calcium-binding capability of the partially purified component correlates with its calcium-channel activity. This indicates that the channel-forming component might be involved in the permeability transition that stimulates its formation.
Gateau-Roesch
O
O
Department of Biochemistry, INSERM 189, Lyon-Sud Medical School, Oullins, France. roesch@lyon-sud.univ-lyon1.fr
Pavlov
E
E
Lazareva
A V
AV
Limarenko
E A
EA
Levrat
C
C
Saris
N E
NE
Louisot
P
P
Mironova
G D
GD
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012965:Sodium Chloride / Q000494:pharmacology
D015220:Calcium Channels; D012965:Sodium Chloride; D002118:Calcium