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468 DIGESTION.
On adding peptone or certain salts the pepsin may be heated to 70
c
C.
for the same time without destruction.
The behavior of pepsin on heating its acid solution is influenced not
only by the degree of acidity, but by the duration of heating and also
by the amount of other bodies in the solution. If an acid (0.2 per cent
HC1) infusion of the calf’s stomach be warmed for several days to about
40 or 45° C, a part of the pepsin is destroyed, but we obtain in this
manner an infusion which still dissolves proteins but has no rennin action
(Hammaesten 1
). The pepsin from different animals acts differently
in this regard and the pepsin of the pike stomach is very quickly destroyed
at 37-40° C.
Pepsin is extraordinarily sensitive to the action of alkalies, not only
caustic, and carbonated, but also against the hydroxides of the alka-
line earths. It is easily made inactive by these substances. If the
action of the alkali is not too strong then, as shown by Pawlow and
Tichomieow,2
the enzyme can in part be reactivated by the addition
of acid if the greater part (about four-fifths), of the alkalinity be neutral-
ized by the addition of acid and then after some hours more acid be added.
If the entire quantity of acid be added at one time the reactivation does
not take place.
The only property which is characteristic of pepsin is that it dissolves
protein bodies in acid but not in neutral or alkaline solutions, with the
formation of proteoses, peptones, and other products.
The methods for the preparation of relatively pure pepsin depend,
as a rule, upon its property of being thrown down with finely divided
precipitates of other bodies, such as calcium phosphate or cholesterin.
The rather complicated methods of Beucke and Sundbeeg are based
upon this property. Pekelhaeing makes use of a prolonged dialysis
and precipitation with 0.2 p. m. HC1.
Very permanent pepsin solutions, from which the enzyme with con-
siderable protein can be precipitated by alcohol, may be prepared by
extraction with glycerin. Solutions having a strong action may also
be prepared by making an infusion of the gastric mucosa of an animal
in acidified water (2-5 p. m. HC1). This is unnecessary, as we can obtain
pure gastric juice according to Pawlow’s method, and also because very
active commercial preparations of pepsin can be bought in the market.
The Action of Pepsin on Proteins. Pepsin is inactive in neutral or
alkaline reactions, but in acid liquids it dissolves coagulated protein
bodies. The protein always swells and becomes transparant before
it dissolves. Unboiled fibrin swells up in a solution containing 1 p. m.
HO, forming a gelatinous mass, and does not dissolve at ordinary tem-
1
Zeitschr. f. physiol. Chem., 56. 2
Ibid., 54.
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