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142 THE PROTEIN SUBSTANCES.
globin, and Fischer and Dorpinghaus 18.3 -per cent from horn sub-
stance.1
.
The leucine obtained by cleavage of protein substances is generally
Z-leucine, which is levorotatory in water solution and dextrorotatory
in acid solution. The leucine prepared synthetically by Hufner 2
from isovaleraldehyde, ammonia, and hydrocyanic acid is optically
inactive. Inactive leucine may also be prepared, by the cleavage of pro-
teins with baryta at 160-180° C, because of a ready racemation. The
e/-/-leucine may be split into the two components by various means, espe-
cially by the preparation of the formal combination.3
On oxidation the leucines yield the corresponding oxyacids (leucinic
acids). Leucine is decomposed on heating, evolving carbon dioxide,
ammonia, and amylamine. On heating with alkalies, as also in putre-
faction, it yields valeric acid and ammonia. On putrefaction it yields
isoamylamine and isocaproic acid.
Leucine crystallizes when pure in shining, white, very thin plates,
usually forming round knobs or balls, either appearing like hyaline, or
with alternating light and dark concentric layers which consist of radial
groups of crystals. By slow heating, leucine melts and sublimes into
white woolly flakes, which are similar to sublimed zinc oxide. At the
same time an odor of amylamine is developed. Quickly heated in a
closed capillary tube, it melts with decomposition at 293-295°.
Leucine, as obtained from animal fluids and tissues is always impure,
and is very easily soluble in water and rather easily in alcohol. Pure
leucine is soluble with difficulty. Pure /- and d-leucine dissolve in 4C-
46 parts water, more readily in hot alcohol, but with difficulty in cold
alcohol. The (/-/-leucine is much less soluble. According to Haber-
mann and Ehrexfeld 4 100 parts of boiling glacial acetic acid dissolve
29.23 parts of leucine. The specific rotation of /-leucine, dissolved in
hydrochloric acid (20 per cent solution) is (a) D = +15.6° according to
Fischer and Warburg. In aqueous solution it is (a) D = —10.40°,
according to F. Ehrlich and Wendel.5
The solution of leucine in water is not, as a rule, precipitated by
metallic salts. The boiling-hot solution may, however, be precipitated
by a boiling-hot solution of copper acetate, and this fact is made use of
in separating leucine from other substances. If the solution of leucine
1
Erlenmeyer and Schoffer, cited from Maly, Chem. d. Verdauungssiifte, in Her-
mann’s Handb. d. Physiol., 5, Theil 2, p. 209; Fischer and his collaborators, ibid., 36.
-Jouni. f. prakt. Chem. (N. F.), 1.
Fischer and Warburg, Ber. d. d. chem. Gesellsch., 38.
*Zeitschr. f. physiol. Chem., 37.
R
Fischer and Warburg, Ber. d. d. chem. Gesellsch., 38; E. Ehrlich and Wendel,
Biochem. Zeitschr., 8.
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