Penetration of amino acids into isolated mitochondria.

It has been shown in a preceding paper (I) that glycine in liver and kidney cells is metabolically inhomogeneous for short time intervals. Intravenously administered radioactive glycine was trapped in a synthetic reaction and found to have greater specific activity than the total cellular glycine recovered simultaneously. The reaction used, hippurate synthesis, is a mitochondrial reaction (2, 3). A number of substances are known not to permeate mitochondria freely, and the possibility that the observed inhomogeneity is due to glycine being one of these substances requires investigation. Sucrose will only partially penetrate into isolated mitochondria (4-7), and the penetration of water into the part not accessible to sucrose is responsible for osmotic swelling of mitochondria (8). Similar but less extensive observations have been made for other substances, such as citrate, succinate, pyruvate, and ATP (7, 9), but such behavior has not yet been demonstrated in viva. The techniques used for these substances as well as the technique in viva described previously (1) have been used to study the penetration of glycine and other amino acids into mitochondria.