Organic Syntheses, Coll. Vol. 1, p.194 (1941); Vol. 5, p.39 (1925).
Human hair (Note 1)
is freed from foreign matter (Note 2)
, washed well with a lukewarm solution of soap (Note 3)
, then twice with cold distilled water, and dried. This washing removes the natural oils from the hair (Note 4)
. Two kilos of the dry, washed hair is pushed into a 12-l. round-bottomed Pyrex flask
, and 4 l. of 20 per cent hydrochloric acid (Note 5)
is added. An air-cooled reflux condenser
, consisting of a wide glass tube
, is attached to the flask. The hair is hydrolyzed by heating on the steam bath (Note 6)
until the biuret reaction is entirely negative; this requires one hundred twenty to one hundred forty-four hours.
The mixture is filtered hot, and the insoluble residue is washed with distilled water. The total filtrate is now partially neutralized with 300 cc. of 40 per cent sodium hydroxide
solution, while the mixture is well stirred and cooled, and then a saturated solution of 3750 g. of crystallized sodium acetate
is added. The Congo red test for mineral acid should then be entirely negative. Care must be taken not to make the solution alkaline
with sodium hydroxide (Note 7)
. After standing for three days at room temperature, the precipitated cystine
is filtered on a suction funnel
. This crude material, containing, in addition to the cystine
, some "humin" pigments and tyrosine
, is dissolved in 3 l. of 3 per cent hydrochloric acid
. The solution is filtered and completely decolorized by two to five treatments with 20–25 g. portions of decolorizing carbon (Norite)
which has been completely freed from calcium phosphate
by boiling with dilute hydrochloric acid
and washing with cold water. The filtrate after decolorizing should be water-clear, or at the most only slightly yellow. If it shows more color, the treatment with decolorizing carbon
should be carried out again. The solution should finally be filtered once by gravity to remove traces of a solid impurity which is apt to pass through the suction funnel.
is precipitated from the clear solution by adding a filtered saturated solution of 900–1000 g. of crystallized sodium acetate
until the Congo red reaction is negative. After standing five to six hours (Note 8)
, the cystine
is filtered and washed twice with 100–200 cc. portions of hot, distilled water to remove the last traces of tyrosine
. By this method the typical colorless hexagonal plates of cystine
are obtained. The yield is 100–106 g.
per cent of the weight of the starting material).
Crude sheep's wool may also be employed, but the yield is not so high (about 2.6 per cent).
Hair obtained from barber shops generally contains matches, paper, hair-pins, and cigarette butts, and similar impurities which should be sorted out by hand as completely as possible. The other principal contamination is sand which causes little trouble and need not be removed.
A high grade of soap should be employed. Hair kept in hot dilute sodium carbonate
solution for one to two hours yields little or no cystine
The oily material may also be removed by extracting with gasoline
, but this procedure involves considerably more labor.
The hydrolysis can be carried out in a much shorter time by heating over a flame or on a sand bath
, but there is great danger of breaking the flask on account of bumping, and of racemizing the cystine
If the mixture is allowed to stand for a longer time, tyrosine
tends to crystallize out with the cystine
may be obtained by the hydrolysis of a large number of proteins. However, the keratins are the only common proteins rich enough in cystine
to serve as a source for this amino acid. Many investigators have devised methods for its isolation from the hydrolytic products of human hair,1
and horse hair.4
The method of Folin5
is the basis for most of the others. The procedure described does not claim to give so high a yield as some of those reported in the literature, but is convenient and gives consistent results.
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