Untitled - D Ank Unlimited

papain 552 papain
+H 3 N
+H 3 N NH 3 +
V L
V H
L Chain
H Chain
C L
C H 1 C H 1
–S–S–
C H 2 C H 2
H Chain
–S–S–
–S–S–
C H 3 C H 3
–S–S–
– OOC COO –
the tissue. It is added in excess, which results in one of its
antigen-binding sites remaining free. After washing, the
PAP is placed in the section, and the rabbit antibody part of
this complex will be bound to the free antigen-binding site
of the linking antibody. The unbound PAP complex is then
washed away by rinsing. A substrate of hydrogen peroxide
and aminoethyl-carbazole (AEC) is placed on the tissue
section, leading to formation of a visible color reaction
product that can be seen by light microscopy. Peroxidase
is localized only at sites where the PAP is bound via
linking antibody and primary antibody to antigen molecules,
permitting the antigen to be identified as an area
H Chain
CL
V H
H Chain
L Chain
V L
NH 3 +
Papain
digestion
+H 3 N
Fab fragment
Antibody Fc fragment
SS SS
+H3 N
V L
V H
L Chain
H Chain
C L
C H 1
–S–S–
Papain digestion of IgG yielding two Fab and one Fc fragments.
S S
of reddish-brown pigment. Tissues may be counterstained
with hematoxylin.
papain
A proteolytic enzyme extracted from Carica papaya used
to digest each immunoglobulin (IgG) molecule into two Fab
fragments and one crystallizable Fc fragment. This aids
efforts to reveal the molecular structure of immunoglobulins.
Papain cleaves the IgG molecule on the opposite side
of the central disulfide bond from pepsin, which cleaves the
molecule to the C terminus side, leading to the formation
of one bivalent F(ab′) 2 fragment in contrast to the univalent
Fab fragments. The Fc fragment of papain digestion has
Fab
SS S S
Papain
digestion
C H 2 C H 2
H Chain
–S–S–
–S–S–
C H 3 C H 3
C H 1
–S–S–
– OOC COO –
The Fab fragment is comprised of one light chain and the variable and C H1 regions of a heavy chain. They are united by disulfide bonds and have a single
binding site for antigen. The heavy chain part of a Fab fragment is referred to as Fd. Further digestion with papain yields and Fc′.
S S
SS
S S
Papain
digestion
Fab
S SS
SS
S S
Papain
digestion
A Fab fragment is comprised of one light chain and the variable and CH1 regions of a heavy chain united by a disulfide bond, with a single binding site for
antigen. The heavy chain part of a Fab fragment is referred to as Fd. Further digestion with papain yields an Fc′.
Fc
Fab
SS
S S
Fabc
SS
Fd
Fc´
H Chain
L chain
C L
V H
H Chain
L Chain
NH 3 +
V L
NH 3 +