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(Received for publication, November 21, 1995; and in revised form, January 26,
1996) The dissociation of the
Volume 271,
Number 15,
Issue of April 12, 1996 pp. 8754-8762
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
3500-kDa hexagonal bilayer (HBL)
hemoglobin (Hb) of Lumbricus terrestris upon exposure to Gdm
salts, urea and the heteropolytungstates
[SiW
O
]
(SiW),
[NaSb
W
O
]
(SbW) and
[BaAs
W
O
]
(AsW) at neutral pH was followed by gel filtration, SDS-polyacrylamide
gel electrophoresis, and scanning transmission electron microscopy.
Elution curves were fitted to sums of exponentially modified gaussians
to represent the peaks due to undissociated oxyHb, D (200 kDa),
T+L (50 kDa), and M (25 kDa) (T =
disulfide-bonded trimer of chains a-c, M = chain d, and L = linker chains). OxyHb dissociation
decreased in the order Gdm
SCN > GdmCl > urea >
GdmOAc and AsW > SbW > SiW. Scanning transmission electron
microscopy mass mapping of D showed 10-nm particles with masses of
200 kDa, suggesting them to be dodecamers (a+b+c)
d.
OxyHb dissociations in urea and GdmCl and at alkaline pH could be
fitted only as sums of 3 exponentials. The time course of D was
bell-shaped, indicating it was an intermediate. Dissociations in SiW
and upon conversion to metHb showed only two phases. The kinetic
heterogeneity may be due to oxyHb structural heterogeneity. Formation
of D was spontaneous during HBL reassembly, which was minimal (
10%) without Group IIA cations. During reassembly, maximal (60%)
at 10 mM cation, D occurs at constant levels (15%),
implying the dodecamer to be an intermediate.
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