1. Shifts of enzymatic activity have been followed during the formation and evolution of the droplets that form in the cells of the proximal convolution of the nephron of the rat after the injection of a 50 per cent solution of egg white in isotonic saline. 2. Twelve hours after injection there is a 35 to 40 per cent decrease in succinoxidase and cytochrome oxidase activities in the fraction containing the larger particles; i.e. mitochondria and droplets in equal concentration. Although after 30 hours the quantitative proportion of droplets and mitochondria is the same as previously, the activities of the fraction have returned to the normal observed originally in the uninjected rat in a corresponding fraction consisting of mitochondria only. 3. The microsome fraction shows an average increase of 35 per cent in oxidative enzyme activities during the early period following injection, and decreases to the original figure in the later period of droplet formation. 4. It is concluded from the shifting pattern of localization of oxidative enzyme activity within the cell particulates that the absorption droplets arise by the incorporation of the mitochondrial elements, which originally contain the highest enzyme activity, with absorbed protein through the intermediate stage of smaller (microsomal) particles.

Animals↗

PubMed1954

Cellular mechanisms of protein metabolism in the nephron. V. The intracellular partition and the incorporation into protein of intravenously injected L-lysine.

Parenteral injection of amino acids resulted in the formation of Gram-positive droplets in the cytoplasm of the proximal convoluted tubule cells of the kidney of the rat within 15 minutes after intravenous administration. At this time the free alpha amino nitrogen in the cortex of the kidney had increased 2-fold. At the end of 1 hour this level was still somewhat higher than that of the control animals. The administration of increasing amounts of the amino acid disclosed the existence of a maximal concentration level in the renal cortex. When it was reached droplets appeared. Fractionation of the cells 15 minutes after the injection of lysine resulted in the recovery of free amino acid in the supernatant fluid but 1 hour after the injection lysine was contained within the particulate protein of the fractions which contain droplets. The increase in lysine was of the order of 2- 3-fold. It is concluded that the mitochondria-droplet complex is a locus of amino acid concentration and metabolism within the cytoplasm of the renal cell. A method is described for the determination of lysine in micro quantities.

Amino Acids↗

PubMed1953

Intracellular localization of succinoxidase and cytochrome oxidase of the kidney cortex.

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Biological Phenomena↗