Labeled plasma proteins obtained from donor dogs, previously fed ϵ-C14-dl-lysine, have been given intravenously to recipient dogs.

The disappearance of labeled globulin from the plasma at a rate considerably faster than albumin has been confirmed.

Evidence suggesting that the mass of protein in solution in the extravascular, extracellular fluid is approximately equal to the plasma proteins in circulation has been derived from a study of the dilution of labeled plasma protein by repeated injections of non-labeled plasma protein.

In a period of 7 days the transfer of C14 from plasma to tissue proteins amounted to between 30 and 40 per cent of the activity in the labeled plasma protein injected intravenously. The conversion was accompanied by a very small loss of activity in the urine and expired air and the activity remained in the lysine residue of the liver and probably of other tissues.

The data presented favor the view that plasma proteins are utilized in the body economy after partial catabolism within the cell area and provide no evidence of complete breakdown to the amino acid level.

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