Jezek P, Borecký J
Department of Membrane Transport Biophysics, Institute of Physiology, Academy of Sciences of the Czech Republic, CZ-14220 Prague 4, Czech Republic.
Am J Physiol. 1998 Aug;275(2):C496-504. doi: 10.1152/ajpcell.1998.275.2.C496.
The physiological role of monocarboxylate transport in brown adipose tissue mitochondria has been reevaluated. We studied pyruvate, alpha-ketoisovalerate, alpha-ketoisocaproate, and phenylpyruvate uniport via the uncoupling protein (UCP1) as a GDP-sensitive swelling in K+ salts induced by valinomycin or by monensin and carbonyl cyanide-p-(trifluoromethoxy)phenylhydrazone in Na+ salts. We have demonstrated that this uniport is inhibited by fatty acids. GDP inhibition in K+ salts was not abolished by an uncoupler, indicating a negligible monocarboxylic acid penetration via the lipid bilayer. In contrast, the electroneutral pyruvate uptake (swelling in ammonium pyruvate or potassium pyruvate induced by change in pH) mediated by the pyruvate carrier was inhibited by its specific inhibitor alpha-cyano-4-hydroxycinnamate but not by fatty acids. Moreover, alpha-cyano-4-hydroxycinnamate enhanced the energization of brown adipose tissue mitochondria, which was monitored fluorometrically by 2-(4-dimethylaminostyryl)-1-methylpyridinium iodide and safranin O. Consequently, we suggest that UCP1 might participate in futile cycling of unipolar ketocarboxylates under certain physiological conditions while expelling these anions from the matrix. The cycle is completed on their return via the pyruvate carrier in an H+ symport mode.
对棕色脂肪组织线粒体中单羧酸转运的生理作用进行了重新评估。我们通过解偶联蛋白（UCP1）研究了丙酮酸、α-酮异戊酸、α-酮异己酸和苯丙酮酸的单向转运，其表现为缬氨霉素或莫能菌素以及羰基氰化物 - p -（三氟甲氧基）苯腙在钾盐中诱导的对GDP敏感的肿胀，以及在钠盐中诱导的肿胀。我们已经证明这种单向转运受到脂肪酸的抑制。在钾盐中GDP的抑制作用不会被解偶联剂消除，这表明单羧酸通过脂质双分子层的渗透可忽略不计。相比之下，由丙酮酸载体介导的电中性丙酮酸摄取（由pH变化诱导的丙酮酸铵或丙酮酸钾中的肿胀）受到其特异性抑制剂α-氰基-4-羟基肉桂酸的抑制，但不受脂肪酸的抑制。此外，α-氰基-4-羟基肉桂酸增强了棕色脂肪组织线粒体的能量化，这通过2-（4-二甲基氨基苯乙烯基）-1-甲基碘化吡啶和番红O进行荧光监测。因此，我们认为UCP1可能在某些生理条件下参与单极酮羧酸盐的无效循环，同时将这些阴离子从基质中排出。当它们通过丙酮酸载体以H⁺同向转运模式返回时，循环完成。
