Hutson S M, Rannels S L
J Biol Chem. 1985 Nov 15;260(26):14189-93.
Efflux of branched chain alpha-keto acids from preloaded rat heart mitochondria was slow at low external pH. Efflux was first order, and measured rate constants, kappa efflux, were 0.104 +/- 0.005 and 0.115 +/- 0.006 min-1 for alpha-ketoisovalerate and alpha-ketoisocaproate (KIC), respectively. Efflux was stimulated significantly by branched chain alpha-keto acids and related carboxylates such as alpha-ketocaproate and alpha-ketovalerate, but not by substrates for the pyruvate transporter. KIC was the preferred substrate, and the apparent exchange K0.5 for KIC was 0.14 +/- 0.10 mM. Exchange was 7-8-fold faster than efflux, and the maximal rate of exchange at saturating concentrations of alpha-ketoisovalerate and KIC appeared to be independent of the metabolite used. It is proposed that branched chain alpha-keto acids cross the inner mitochondrial membrane on a specific transporter. Transport occurs with a proton, i.e. by proton symport, and is sensitive to inhibition by cinnamic acid derivatives.
在低外部pH值下，预先加载的大鼠心脏线粒体中支链α-酮酸的流出速度较慢。流出呈一级反应，α-酮异戊酸和α-酮异己酸（KIC）的测量速率常数κ流出分别为0.104±0.005和0.115±0.006 min⁻¹。支链α-酮酸和相关羧酸盐（如α-酮己酸和α-酮戊酸）可显著刺激流出，但丙酮酸转运体的底物则无此作用。KIC是首选底物，KIC的表观交换K0.5为0.14±0.10 mM。交换速度比流出快7 - 8倍，在α-酮异戊酸和KIC饱和浓度下的最大交换速率似乎与所用代谢物无关。有人提出支链α-酮酸通过特定转运体穿过线粒体内膜。转运与质子一起进行，即通过质子同向转运，并且对肉桂酸衍生物的抑制敏感。
