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.

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