Presence of a Phosphatido-peptide Fraction in Liver Cell Membrane and its Possible Role in the Active Transport of Ammo-acids

Abstract

PREVIOUS work in this laboratory has shown that a phosphatido-peptide fraction becomes promptly labelled during the perfusion of the isolated rat liver with rat blood containing labelled amino-acids, and reaches a maximum in its radioactivity a few minutes after the start of the experiment^1–3. The reaction is strongly inhibited by metabolic inhibitors, such as ethionine, potassium cyanide and 2,4-dinitrophenol. It was also shown that the phosphatido-peptide contained in the 1,000 × g fraction of liver homogenates, which contains at least a large part of cell membranes⁴, incorporates the radioactivity more rapidly than that contained in the mitochondrial or in the microsomal fraction and in the 105,000 × g supernatant. The radioactivity bound to the phosphatido-peptide fraction was released after incubation with a liver cathepsin preparation; other proteolytic enzymes so far tested were devoid of such a property.