Appearance of Serine upon Alkaline Incubation of Iodinated Polytyrosine


3,5-DIIODOTYROSINE is known to be a precursor of thyroxine1,2. The formation of thyroxine from two diiodotyrosine residues leads obviously to the formation of a three-carbon α-amino-acid. Thus simple dismutation would lead to alanine2,3, while an oxidative mechanism involving the formation of a labile intermediate of quinonic structure should yield serine1,2,4. In the latter case, serine could be formed either by the direct hydrolysis of the labile intermediate4, or by the hydration of dehydroalanine formed upon molecular dissociation of the labile intermediate1. If the unsubstituted 3,5-diiodotyrosine is used in the reaction, dehydroalanine formed may also be hydrolysed to pyruvic acid and ammonia. Johnson and Tewkesbury identified these two products in their reaction mixture4. Pitt-Rivers identified alanine among the products of the aerobic incubation of N-acetyl-L-diiodotyrosine chromatographically, but stated that alanine could have been formed afterwards from pyruvic acid5.

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  1. 1

    Harington, C. R., J. Chem. Soc., 193 (1944).

  2. 2

    Roche, J., and Michel, R. “Advances in Protein Chem.”, 6, 253 (1951); Physiol. Rev., 35, 583 (1955).

  3. 3

    Roche, J., Michel, R., and Nunez, J., Bull. Soc. Chim. Biol., 37, 229 (1955).

  4. 4

    Johnson, T. B., Tewkesbury, jun., L. B., Proc. U.S. Nat. Acad. Sci., 28, 73 (1942).

  5. 5

    Pitt-Rivers, R., Biochim. Biophys. Acta, 2, 311 (1948); Biochem. J., 43, 223 (1948).

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    Katchalski, E., and Sela, M., J. Amer. Chem. Soc., 75, 5284 (1953).

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    Bowden, C. H., and Maclagan, N. F., Biochem. J., 56, vii (1954).

  8. 8

    Tatum, E. L., and Lederberg, J., J. Bacteriol., 53, 673 (1947).

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