The Interaction Of Serum Albumins With Calcium Page 4

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326
N. H. MARTIN AND D. J. PERKINS
I950
The recent studies of Scatchard, Scheinberg &
Armstrong (1950) on the interaction of protein with
chloride ions would, in a detailed treatment, entail
a
correction of Donnan coefficients, but as all our
experiments were carried out over a limited and
comparable range of pH and chloride concentration
we have not introduced such a correction.
The variations in binding shown in the varying
samples of ox albumin suggest two possibilities: that
the different techniques used for separation of
albumin have modified the calcium-binding capacity
of the molecule
to different extents, or that the
fractionating methods are separating out different
albumins. The other fractionated albumin shown in
Table
3 was kindly given to us by Dr R. A. Kekwick.
He had rejected the specimen because for indepen-
dent
reasons it was regarded as below standard.
Electrophoretic
analysis was perfectly satisfactory,
and there was no indication from the behaviour of
the material in solution that it had been modified;
nevertheless, as the table shows, we were unable to
demonstrate any calcium binding. The ether-
fractionated
concentrates (2), which had been
handled with care, are shown in Table 2, and give
calcium-binding capacities comparable with those of
the methanol-fractionated (1) and the ethanol-
fractionated five times recrystallized product (4).
It seems certain, therefore, that molecular modifi-
cation can occur during fractionation. Table 2 shows
analyses of three carefully purified albumins given
us
by the
courtesy of Prof. W. L.
Hughes of Harvard.
The albumin ten times recrystallized with decanol
(5) had
a
calcium-binding capacity lower than either
the five times recrystallized albumin (4) or the ether-
fractionated (2) and methanol-fractionated (1) crude
materials. These albumins had comparable calcium-
binding capacities. The product recrystallized
with
mercury (6) had a considerably higher calcium-
binding capacity. All these three materials
stem
from an ethanol fractionation and had been pre-
pared with every care. The possibility arises, there-
fore, that the process of recrystallization had resulted
in the separation of two albumins present in normal
serum and differing in their calcium-binding
capacity. We appreciate that without accurate yield
tables for these purified specimens it is not possible
to be dogmatic, but we submit that the data are
indicative of the presence of at least two albumins
in normal human serum.
SUMMARY
1. Purified albumins from differing species have
been examined for their calcium-binding capacities.
A species difference is observed.
2. Albumins from individual
species purified by
varying techniques show variations in calcium-
binding capacities.
3. These variations are
discussed,
and it is sug-
gested that, while
some
results suggest modifications
of the albumin
during purification,
there is evidence
that certain
techniques
of
crystallization
result in
the fractionation of distinct albumins.
Our thanks
are
due
to
the
Biophysics Department
of the
Lister Institute for the facilities
granted
to us.
REFERENCES
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