Full resolution (JPEG) - On this page / på denna sida - II. The Protein Substances - I. Simple Proteins - B. Albuminoids or Albumoids
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114 THE PROTEIN SUBSTANCES.
was the first to prove positively the abundant occurrence of cystine in
the cleavage products. Morner obtained from ox horn, human hair,
and the shell-membrane of the hen’s egg 6.8, 13.92, and 7.62 per cent
cystine calculated on the basis of the dry substance. Buchtala l
obtained
the following amounts of cystine from the respective keratin forma-
tions, namely, 12.98-14.53 per cent from human hair, 5.15 per cent from
nails, 7.98 per cent from horsehair, 3.20 per cent from horse hoofs, 7.27
per cent from ox hair, 5.37 per cent from ox hoofs, 7.22 from pig bristles,
2.17 per cent from pig hoofs, 6.30 per cent from goose feathers, 2.14
per cent from chicken spurs, 1.88 per cent from the epidermis scales of
chicken feet and 4.7 per cent from elephant epidermis. From the amount
of sulphur split off by alkali, Morner concludes that, at least in ox
horn and human hair, all the sulphur exists as cystine. Galimard 2
was able to get only a qualitative test for cystine in the keratin of the
adder eggs. Suter, Morner, and Friedmann 3
have obtained ct-thio-
lactic acid as a hydrolytic cleavage product of the keratin substances.
The last-mentioned investigator was also able to detect thioglycolic acid
in the cleavage products of wool.
The shell membrane of the hen’s egg, and the eggshells of amphibians
and certain fishes are, as above mentioned, ordinarily classified as kera-
tins. These bodies among themselves, as well as on comparison with
other keratins, show a marked difference in properties, this being very
evident from the tabulation on page 115.
The large quantity of cystine in the keratins is considered as espe-
cially characteristic, and they differ in this regard from^he other proteins.
The shell membrane of the hen’s egg behaves like a keratin in regard to the
large amount of cystine contained, but differs essentially by the absence
of tyrosine. It is remarkable that the egg membrane of the Selachii,
which biologically is analogous with ovokeratin, differs from the typical
keratins by the absence of cystine, while it contains, on the contrary,
large amounts of tyrosine. The typical keratins differ among them-
selves in regard to composition, thus the keratin from the sheep hoofs
contains 2 per cent phenylalanine, while this ammo-acid is absent in the
keratin of hair and feathers. It is difficult to say whether or not this
is due to a difference in the purity of the bodies or not. The keratins
investigated chemically, thus far, do not form a sufficient characteristic
group.
1
Morner, ibid., 34 and 42; Emmerlinp:, Ref. in Chemiker Zeitung, 1894; Buchtala,
Zeitschr. f. physiol. Chem., 52, fii*, and 78.
*Chem. Centralbl, II, 1905.
1
Suter, Zeitschr. f. physiol. Chem., 20; Morner. ibid., 42; Friedmann, Hofmeister’s-
Beitrage, 2.
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