The physiology of the amino acids / by Frank P. Underhill.

  • Underhill, Frank P. (Frank Pell), 1877-1932.
Date:
1915
Catalogue details

Licence: In copyright

Credit: The physiology of the amino acids / by Frank P. Underhill. Source: Wellcome Collection.

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    tisic acid is a step in the degradations of these amino acids has been doubted by Dakin who believes that there is in these subjects an abnormal formation of homogentisic acid as well as an inability to destroy it once formed. In accord with this idea he has shown how tyrosine and phenylalanine may be destroyed with- out homogentisic acid as an intermediary product (see p. 103). On the other hand, it has been demonstrated by Abderhalden that normal individuals may eliminate homogentisic acid when excessive quantities of tyrosine are fed. Also the administration of tyrosine or phenyl- alanine, or of foods rich in tyrosine, that is proteins, causes a significant increase in the excretion of homo- gentisic acid. If alkaptonurics live on a protein-free diet for short periods of time the excretion of homo- gentisic acid is markedly diminished, but does not dis- appear entirely. Undoubtedly the aromatic amino acids formed from tissue metabolism do not suffer destruction to any greater extent than those introduced into the blood from the food protein. Why an alkap- tonuric individual fails to destroy the tyrosine radicle is still a matter of conjecture. Cystinuria and Diaminuria Under ordinary circumstances cystine, the sulphur bearing amino acid fails to appear in the excreta, prob- ably undergoing extensive destruction. The sulphur is oxidized to sulphuric acid and eliminated as a sul- phate in the urine. In certain individuals, however, cystine appears in the urine and owing to its relatively