JBC, Vol. 252, Issue 12, 4326-4329, Jun, 1977
Limited pepsin digestion of human plasma albumin
J. Heaney-Kieras and T. P. King
Limited pepsin digestion of human plasma albumin at pH 3.5 and 0 degrees in
the presence of octanoate caused cleavage at residue 307 of the albumin
molecule to yield two fragments. Thw two fragments corresponding to the
NH2- and the COOH-terminal halves of the molecule were isolated in yields
of about 15%. The COOH-terminal fragment is a mixture in which about 85% of
the molecules had an additional cleavage at residue 422 of the albumin
molecule. The COOH-terminal fragment with the additional cleavage at
residue 422 contains two peptides which are linked by a disulfide bridge at
residues 391 and 437 of the albumin molecule. Both the NH2- and the
COOH-terminal fragment of human albumin showed no detectable binding of
octanoate anions, that is, less than 1/170 of the binding constant of the
primary site of human albumin. These findings differ from earlier
observations on limited pepsin digestion of bovine plasma albumin where the
corresponding COOH-terminal fragment had the octanoate-binding activity,
about 1/8 of the primary binding constant of bovine albumin, while the
NH2-terminal fragment did not. The COOH-terminal fragment of bovine albumin
did not have cleavage at residue 422 as in the corresponding fragment of
human albumin. However, it is not clear that the loss of octanoate-binding
activity of fragment C of human albumin is a direct consequence of the
cleavage at residue 422.
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