Branca D, Roberti M S, Vincenti E, Scutari G
Dipartimento di Chimica Biologica, Università di Padova, Italy.
Arch Biochem Biophys. 1991 Nov 1;290(2):517-21. doi: 10.1016/0003-9861(91)90575-4.
2,6-Diisopropylphenol, a general anesthetic, was previously reported to reduce the transmembrane electrical potential in isolated rat liver mitochondria without affecting the rate of ATP production. This effect appeared to contrast with the generally accepted chemiosmotic mechanism for oxidative phosphorylation. In this study we further examined the influence of 2,6-diisopropylphenol on the production of ATP by isolated mitochondria and we studied its effect on the permeability of the inner mitochondrial membrane to protons. In order to clarify the effects of 2,6-diisopropylphenol on mitochondrial ATP production the activities of the adenine nucleotide translocator and the ATP synthetase were evaluated. The results obtained indicate that the depression of the transmembrane electrical potential elicited by 2,6-diisopropylphenol decreased the activity of the ATP synthetase (as expected in the chemiosmotic model for energy coupling), but not that of the adenine nucleotide translocator. The decrease of the ATP synthetase activity, however, did not result in an apparent inhibition of the overall rate of ATP production in isolated mitochondria due to the rate-limiting effect of the adenine nucleotide translocator in this process. Moreover 2,6-diisopropylphenol was found to increase the permeability to protons of the inner mitochondrial membrane; this effect became more marked as the pH of the incubation medium was increased, demonstrating that it involved the dissociated form of 2,6-diisopropylphenol. These observations suggested that 2,6-diisopropylphenol affected oxidative phosphorylation by acting as a mild protonophore and that its effectiveness was limited by the low fraction of phenol dissociated at near-physiological pH.
2,6-二异丙基苯酚是一种全身麻醉剂，此前有报道称它能降低离体大鼠肝线粒体的跨膜电位，而不影响ATP的产生速率。这种效应似乎与普遍接受的氧化磷酸化化学渗透机制形成对比。在本研究中，我们进一步研究了2,6-二异丙基苯酚对离体线粒体ATP产生的影响，并研究了其对线粒体内膜质子通透性的作用。为了阐明2,6-二异丙基苯酚对线粒体ATP产生的影响，我们评估了腺嘌呤核苷酸转位酶和ATP合酶的活性。所得结果表明，2,6-二异丙基苯酚引起的跨膜电位降低会降低ATP合酶的活性（正如能量偶联的化学渗透模型所预期的那样），但不会降低腺嘌呤核苷酸转位酶的活性。然而，由于腺嘌呤核苷酸转位酶在此过程中的限速作用，ATP合酶活性的降低并未导致离体线粒体中ATP产生的总体速率受到明显抑制。此外，发现2,6-二异丙基苯酚可增加线粒体内膜对质子的通透性；随着孵育介质pH值的升高，这种效应变得更加明显，表明它涉及2,6-二异丙基苯酚的解离形式。这些观察结果表明，2,6-二异丙基苯酚通过作为一种温和的质子载体来影响氧化磷酸化，并且其有效性受到在接近生理pH值下苯酚解离比例低的限制。
