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Evidence for Polypeptide Synthesis in the Caiman from Mixtures Deficient in Essential Amino Acids¹

Department of Biochemistry, Louisiana State University Medical Center, New Orleans, Louisiana 70112

Caimans were injected with a complete balanced mixture of free amino acids in the same ratio as that found in fish muscle (complete mix) and with mixtures of the same composition and ratio except that three essential amino acids were omitted (incomplete mix). Plasma was analyzed, and the half-life of each amino acid was determined and compared with the previously determined half-life of the same amino acid when given alone. Whereas there were 30-fold differences in the half-lives among the amino acids when given singly, every amino acid component of both mixtures disappeared at about the same rate. Essential amino acids in the balanced mixes disappeared several times as fast as they did when given singly. Removal of amino acids from the plasma after injection of unbalanced mixes was much slower than that from balanced mixes, and the amino acids disappeared at different rates. The half-lives of injected single amino acids commonly found in proteins were reduced greatly by subsequent injection of balanced complete or incomplete mixes, while the half-lives of amino acids not found in proteins were unaffected. Inhibition of protein synthesis by cycloheximide lengthened the half-lives of all the amino acids in both the complete and incomplete mixes, and acceleration of protein synthesis by insulin injection shortened the half-lives of the amino acids in both mixes. It is postulated that immediate protein synthesis follows injection of complete balanced mixtures, and that some type of macromolecule synthesis follows injection of balanced but incomplete mixtures, balanced except for the omission of three amino acids.

KEY WORDS: • amino acid disposal • caiman

¹ Supported in part by a grant from the Edward G. Schlieder Foundation.

Manuscript received 24 August 1973.