The presence of two classes of high-affinity cyclosporin A binding sites in mitochondria. Evidence that the minor component is involved in the opening of an inner-membrane Ca(2+)-dependent pore.
The inner membrane of rat liver mitochondria contains a reversible Ca(2+)-dependent pore, opening of which is largely blocked by cyclosporin A. Analyses of [3H]cyclosporin binding to rat liver mitochondria demonstrate two classes of high-affinity binding site with capacities of less than 5 pmol and approximately 60 pmol cyclosporin.mg mitochondrial protein-1 in addition to partitioning into membrane phospholipids (0.03 pmol.mg mitochondrial protein.nM-1). Direct measurement [14C]sucrose entry into the matrix space indicates that cyclosporin A inhibits pore opening by interacting with the low-capacity sites. The same low-capacity sites (Kd cyclosporin, 8 nM) are possibly attributable to peptidylprolyl cis-trans-isomerase, although investigation of pore state interconversion from the rapid kinetics of [14C]sucrose entrapment in the matrix space does not indicate that cyclosporin-sensitive prolyl isomerization occurs at the actual step of pore opening/closure. It is suggested that the low-capacity cyclosporin-binding component may stabilize the open pore state; this is supported by the observations that Ca2+ decreases cyclosporin binding to this component and that cyclosporin brings about closure of the pre-opened pore. The implications for the possible number of functional pores in mitochondria are discussed.
McGuinness
O
O
Department of Biochemistry, University College London, England.
Yafei
N
N
Costi
A
A
Crompton
M
M
D000591:Amino Acid Isomerases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D015220:Calcium Channels / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D003524:Cyclosporins / Q000378:metabolism*; D004533:Egtazic Acid; D005230:Fatty Acids, Nonesterified / Q000032:analysis; D008297:Male; D008930:Mitochondria, Liver / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D019696:Peptidylprolyl Isomerase; D051381:Rats; D011919:Rats, Inbred Strains; D013367:Submitochondrial Particles / Q000201:enzymology / Q000378:metabolism
D015220:Calcium Channels; D002352:Carrier Proteins; D003524:Cyclosporins; D005230:Fatty Acids, Nonesterified; D004533:Egtazic Acid; D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase