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152 THE PROTEIN SUBSTANCES.
was first found by E. Schulze and Barbieri l
in etiolated lupin sprouts.
It is produced in the acid cleavage of protein substances in quantities
rarely above 5-6 per cent. It has been prepared synthetically in several
ways by Erlenmeyer, Jr., Sorensen and E. Fischer, Wheeler and
Hoffman.2
The /-phenylalanine crystallizes in small, shining leaves or fine needles
which are rather difficultly soluble in cold water but readily soluble in
hot water. The solution has a faint bitter taste. A 5-per cent solution
acidified with hydrochloric acid or sulphuric acid is precipitated by
phosphotungstic acid, while a more dilute solution is not precipitated.
On putrefaction, phenylalanine yields phenylacetic acid. On heat-
ing with potassium dichromate and sulphuric acid (25 per cent) an odor
of phenylacetaldehyde is produced and benzoic acid is formed. In
aqueous solution it has a rotation of (a) D = — 35.1°. The phenyliso-
cyanate-1-phenylalanine melts at about 182° C.
/-Tyrosine (p-oxyphenyl-a-aminopropionic acid),
C6H4 (OH)
C9HiiN03 = CH2
CH(NH2)’
COOH
is produced from most protein substances under the same conditions
as leucine, which it habitually accompanies. The largest quantity of
tyrosine obtained from animal proteins was about 10-13 per cent (see
tables, pages 106, 107, 115 and 125). In gelatin and a few keratins
tyrosine is absent. It is especially found with leucine, in large quantities,
in old cheese (Tupos), from which it derives its name. Tyrosine has not
been found with certainty in perfectly fresh organs. It occurs in the
intestine during the digestion of protein substances, and it has about
the same physiological and pathological importance as leucine.
Tyrosine was prepared by Erlenmeyer and Lipp from p-amino-
phenylalanine by the action of nitrous acid, and according to another
method by Erlenmeyer and Halsey.3 On fusing with caustic alkali
it yields p-oxybenzoic acid, acetic acid, and ammonia. On putrefaction
it may yield oxyphenylethylamine, oxyphenylpropionic acid, oxyphenyl-
acetic acid, p-cresol and phenol.
1
Ber. d. d. chem. Gesellsch., 14, and Zeitschr. f. physiol. Chem., 12.
2
Erlenmeyer, Annal. d. Chem. u. Pharm., 275; Sorensen, Zeitschr. f. physiol.
Chem., 44; E. Fischer, Ber. d. d. chem. Gesellsch., 37; Wheeler and Hoffman, Amer.
Chem. Journ., 45.
3
Erlenmeyer and Lipp, Ber. d. d. chem. Gesellsch., 15; Erlenmeyer and Halsey,
ibid., 80.
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