The uptake of a variety of amino acids into nuclear proteins of tumors and other tissues.

In a recent report, (2) it was noted tha t Llysine-U-C 14 was incorporated to a greater extent into the nuclear proteins of t ransplantable ra t tumors than into the nuclear proteins of a variety of other tissues. The greater incorporation of the labeled lysine into the histones of the tumor was evidenced by (a) the high specific act ivi ty (S.A.) of the histones, as compared either with the specific activities of other proteins in the tumor or with the specific activities of histones of other tissues and (b) the higher percentage of the total isotope in the histones of the tumor than in histones of other tissues. As a result of these initial findings, two avenues of research have been pursued in this laboratory in recent months. In the first of these, which forms the subject mat te r of the present report, the findings obtained with lysine have been amplified and modified through the s tudy of the incorporation of seventeen radioactive amino acids into proteins of various fractions of the cells of liver, kidney, spleen, pancreas, small intestine, and Walker tumor. The tissues studied were selected because of the high specific act ivi ty of their proteins following the injection of L-lysine-U-C 14 (~). In the second approach, the histones of these tissues have been subjected to chromatographic separation as well as separation by differential precipitation (4). In the present series of experiments, 10 gc. of a given amino acid were injected into a tumorbearing rat, and 60 minutes later the tissues indicated above were excised and fractionated as indicated previously (~). I t was found tha t there was marked variat ion in the uptake and the distribution of the different amino acids. The relative