Coupling factor B is a component of the Fo proton channel of mitochondrial H+-ATPase

The proximal N-terminal amino acid residues are required for the coupling activity of the bovine heart mitochondrial factor B

Treatment of the recombinant bovine factor B with trypsin yielded a fragment (amino acid residues 62-175) devoid of coupling activity. Removal of the N-terminal Trp2-Gly3-Trp4 peptide resulted in a significant loss of coupling activity in the FB(DeltaW)(2)(-W)(4) deletion mutant. Sucrose density gradient centrifugation demonstrated co-sedimentation of recombinant factor B with the ADP/ATP carrier, which is present in preparations of H(+)-translocating F(0)F(1)-ATPase, but not in preparations of complex V. The N-terminally truncated factor B mutant FB(DeltaW)(2)(-W)(4) did not co-sediment with the ADP/ATP carrier. Recombinant factor B co-sedimented with partially purified membrane sector F(0), extracted from F(1)-stripped bovine submitochondrial particles with n-dodecyl-beta-d-maltoside. Factor B inhibited the passive proton conductance catalyzed by F(0) reconstituted into asolectin liposomes. A factor B mutant, bearing a photoreactive unnatural amino acid pbenzoyl-l-phenylalanine (pBpa) substituted for Trp2, cross-linked with F(0) subunits e and g as well as the ADP/ATP carrier. These results suggest that the N-terminal domain and, in particular, the proximal N-terminal amino acids are important for the coupling activity and protein-protein interactions of bovine factor B.

Why is inorganic phosphate necessary for uncoupling of oxidative phosphorylation by Cd2+ in rat liver mitochondria?

The phosphate (Pi)-dependent uncoupling action of Cd2+ in oxidative phosphorylation in rat liver mitochondria was studied mainly in terms of Pi transport. Cd2+ at 2 microM caused full uncoupling in the presence of 10 mM Pi, but no uncoupling in the absence of Pi. Cd2+ released state 4 respiration after a certain lag-time, and then the respiration increased progressively with time. After its addition, Cd2+ was taken up by mitochondria in a similar period to the lag time before respiratory release. KIH-201, a potent and specific inhibitor of Pi transport via the Pi/H+ symporter, abolished the uncoupling completely. Cd2+ caused dissipation of the electric transmembrane potential (delta psi) and swelling of mitochondria in a Pi-dependent manner. Uncoupling by Cd2+ was found to take place in parallel with the uptake of Pi into mitochondria via the Pi/H+ symporter, suggesting that the uncoupling was due to acceleration of H+ influx through the Pi/H+ symporter activated by Cd2+.

Amino-terminal amino acid sequence of beef heart mitochondrial coupling factor B

Bovine heart mitochondrial coupling factor B was isolated and purified to homogeneity in its active form. The amino-terminal amino acid sequence of the alkylated protein was determined. Two chains with exactly the same sequence except for the presence of an additional Phe at the amino-terminus on one of them were obtained. The 55 amino acid sequence appears to be largely hydrophilic with several charged amino acid residues. This sequence showed no homology with the E. coli unc operon, oligomycin sensitivity conferring protein, or coupling factor 6 or any protein in the data base.

Mitochondrial sulfhydryl groups under oligomycin-inhibited, aging, and uncoupling conditions: beneficial influence of cardioprotective drugs

Uncoupling, oligomycin-inhibited, and aging/swelling conditions comprise three models for mitochondrial dysfunction. In these models, the effects of cardioprotective agents on rat heart mitochondrial membrane -SH reactivity have been studied. For -SH detection two different chromophores were used: dithionitrobenzoate (NbS2) and monobromobimane (MB). The objective of this study is to reveal the influence of three cardioprotective substances against the loss of membrane -SH reactivity: (i) The thiol reagent 2-mercaptopropionylglycine (MPG) prevents the decrease of thiols caused by carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP), aging, and oligomycin measured with MB and NbS2, and the diminution by oleate detected with MB. The small amount of MPG (6 nmol/mg protein), necessary for the protection, agrees with oligomycin sensitivity of the -SH groups concerned. (ii) The active metabolite of molsidomine, 3-morpholinosydnonimine (SIN-1), protects against the decrease of thiols by FCCP, oleate, and aging monitored with MB. In the case of oligomycin -SH groups accessible to NbS2 are protected. (iii) Another antianginal drug, isosorbidedinitrate (ISDN) does not protect membrane thiol groups. In contrast to SIN-1, ISDN probably requires enzymatic activation. It is suggested that MPG as well as SIN-1 may help to restitute the original -SH status of the mitochondrial membrane.