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April 8, 1933


JAMA. 1933;100(14):1129. doi:10.1001/jama.1933.02740140053030

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To the Editor:  —In The Journal, Dec. 24, 1932, appeared an interesting article entitled "Cystine Nephrolithiasis," by George H. Ewell, M.D. Attention should, however, be directed to the following misstatements in Dr. Ewell's communication:

  • "Chemically, cystine is a complex organic compound and belongs in the amino-acid group, the only one that contains sulphur, the latter being about 25 per cent of its content."

  • "Feeding experiments on dogs and rats have shown that it [cystine] is an essential amino-acid necessary for growth and maintenance of body weight, and no other substance can replace it."

  • "The chemical formula of cystine is [S.CH2CH(NH2). CCOOH]2 and by oxidation is broken up into two molecules of cystinic acid; these substances are stored in the body tissue and play a great rôle in oxidation processes."

Cystine is not the only sulphur-containing amino-acid found in proteins; methionine also contains sulphur. Furthermore, the latter amino-acid is apparently capable

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