The uptake of ornithine and lysine by rat liver mitochondria

Ornithine and lysine are taken up by rat liver mitochondria with an apparent Km of 1.3 and 2.4 mM, respectively. Neither lysine methylester alpha-N-acetyl lysine, nor epsilon-N-acetyl lysine inhibits the uptake of either ornithine or lysine. The zwitterionic form of these amino acids is taken up by liver mitochondria. Lysine inhibits the uptake of ornithine and vice versa. The inhibition is in both cases of the mixed type. Arginine strongly inhibits the uptake of both ornithine and lysine. Alkalinization of the mitochondrial matrix decreases the rate of uptake of ornithine and of lysine, while acidification of the mitochondrial matrix increases these rates. It is concluded that ornithine and lysine are taken up via a common carrier in exchange for H+.