Biology Reference
In-Depth Information
Table 2.
Crystallization of BR in Swollen Lipidic
L
3
Mesophases.
a
Bacteriorhodopsin
crystals
Additive
8
11
15
18
(%)
None
MPD
(%)
10
14
18
22
None
PPO
(%)
7
12
17
22
+
Jeffamine M-600
(%)
27
30
35
40
None
1,4-Butanediol
(%)
18
22
26
30
None
t-Butanol
(M)
0.6
1.2
1.7
2.2
None
KSCN
a
The different colors of the cells correspond to the results of visual observation of the behavior of BR
after the addition of the additives. Purple corresponds to stable BR and red, pink, yellow and white
correspond to different levels of BR degradation.
Crystallization from vesicles
The third approach is crystallization from vesicles with a very large pro-
tein/lipid ratio (Takeda
et al
., 1998). It was previously observed that pur-
ple membranes of
Halobacterim salinarum
(a two-dimensional BR
crystal where the trimers of the protein are tightly packed in a perfect
hexagonal lattice) treated with the detergent n-octyl-b-D-glucopyranoside
under certain conditions lead to the creation of spherical protein clusters
with a diameter of
50 nm which are hexagonal close-packed (Kouyama
et al
., 1994). This was revealed by atomic force microscopy images of the
crystal surface. Electron micrographs of mechanically disintegrated crys-
tals show that the inside of the protein cluster is filled with the mother
liquor. The crystal is made up of hollow protein clusters. When disinte-
grated crystals are illuminated in the presence of a lipophilic anion, a
significant alkalization of the external medium occurs. This result demon-
strates that the protein cluster contains native lipids and that the cytoplas-
mic side of the protein faces the external medium. It has been claimed that
X-ray diffraction patterns and the observed diameter of the spherical shell
suggest that about 200 bacteriorhodopsin trimers are aligned on a polyhe-
dral surface lattice. Vesicle formation from purple membranes was
studied in detail in Denkov
et al
. (1998).
∼
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