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Published June 1, 1949 | Published
Journal Article Open

The incorporation of labeled lysine into the proteins of guinea pig liver homogenate


When C14-labeled lysine is incubated with guinea pig liver homogenate, α-aminoadipic, α-ketoadipic, and glutaric acids are formed from the lysine (1). These transformations were established by finding the radioactivity of the C14 tracer in the metabolic products. The homogenate proteins coagulated by boiling at pH 5 also contained radioactivity. The counts given by the proteins corresponded to about 0.02 to 0.03 per cent of that added as lysine; the extent of lysine incorporation into the proteins was of the same order of magnitude as Melchior and Tarver (2) had found after incubating S35-labeled methionine and Winnick et al. (3, 4) C14-labeled glycine with rat tissue homogenates. Yet we could not satisfy ourselves that the radioactivity remaining in the proteins in our experiments, although it persisted through exhaustive extraction, did not come from traces of adsorbed radioactive lysine. Some counts were found in the protein when the homogenate was boiled prior to incubation with isotopic lysine.

Additional Information

© 1949 American Society of Biological Chemists. Received for publication, December 29, 1948. The microanalyses were carried out by Mr. G. Swinehart. The authors were assisted by A.A. Dvorsky, H.E. Jeffrey, M. Keighley, and A. Tollestrup. This work is a part of that done under contract with and joint sponsorship of the Office of Naval Research, United States Navy Department, and the United States Atomic Energy Commission. The C14 used in this investigation was supplied by the Monsanto Chemical Company, Clinton Laboratories, Oak Ridge, Tennessee, and obtained on allocation from the United States Atomic Energy Commission.

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