Potassium channels exclude the smal

Potassium channels exclude the smaller
alkali metal cations Li1 (radius 0.60 Å) and
Na1 (0.95 Å) but allow permeation of the
larger members of the series Rb1 (1.48 Å)
and Cs1 (1.69 Å). In fact, Rb1 is nearly a
perfect K1 (1.33 Å) analog because its size
and permeability characteristics are very
similar to those of K1. Because they are
more electron dense than K1, Rb1 and Cs1
allow visualization of the locations of permeant
ions in the pore. By difference electron
density maps calculated with data from
crystals transferred into Rb1-containing
(Fig. 6a) or Cs1-containing (Fig. 6b) solutions,
multiple ions are well defined in the
pore. The selectivity filter contains two
ions (inner and outer ions) located at opposite
ends, about 7.5 Å apart (center to
center). In the Rb1 difference map, there
actually are two partially separated peaks at
the inner aspect of the selectivity filter.
These peaks are too close to each other (2.6
Å) to represent two simultaneously occupied
ion binding sites. We suspect that they
represent a single ion (on average) in rapid
equilibrium between adjacent sites. The
single inner ion peak in the Cs1 difference
map undoubtedly reflects the lower resolution
at which the map was calculated (to 5
Å for Cs1 versus 4.0 Å for Rb1), because
the Rb1 difference map, when calculated at
the same lower resolution, also shows only a
single peak at the Cs1 position. The Rb1
positions correspond to strong peaks (pre-sumably, K1 ions) in a high contour native
electron density map (not shown). Thus,
the selectivity filter contains two K1 ions.
A third weaker peak is located below the
selectivity filter at the center of the large
cavity in the Rb1 difference map (Fig. 6a,
cavity ion) and in the Cs1 difference map
at a lower contour (not shown). Electron
density at the cavity center is prominent in
MIR maps, even prior to averaging (Fig. 6c,
lower diffuse peak). The difference electron
density maps show this to be related to the
presence of one or more poorly localized
cations situated at least 4 Å away from
the closest protein groups.

ผลลัพธ์ (ไทย) 3:

Potassium channels exclude the smaller
alkali metal cations Li1 (radius 0.60 Å) and
Na1 (0.95 Å) but allow permeation of the
larger members of the series Rb1 (1.48 Å)
and Cs1 (1.69 Å). In fact, Rb1 is nearly a
perfect K1 (1.33 Å) analog because its size
and permeability characteristics are very
similar to those of K1. Because they are
more electron dense than K1, Rb1 and Cs1
allow visualization of the locations of permeant
ions in the pore. By difference electron
density maps calculated with data from
crystals transferred into Rb1-containing
(Fig. 6a) or Cs1-containing (Fig. 6b) solutions,
multiple ions are well defined in the
pore. The selectivity filter contains two
ions (inner and outer ions) located at opposite
ends, about 7.5 Å apart (center to
center).ในแผนที่มีจริง ๆความแตกต่าง Rb1 ,
2 บางส่วนแยกยอดที่
ด้านภายในของตัวกรองหัวกะทิ .
ยอดเหล่านี้อยู่ใกล้กับแต่ละอื่น ๆด้วย ( 2.6
Å ) เพื่อแสดงสองพร้อมกันครอบครอง
ไอออนผูกพันเว็บไซต์ เราสงสัยว่าพวกเขา
เป็นตัวแทนของไอออนเดี่ยว ( เฉลี่ย ) สมดุลอย่างรวดเร็ว
ระหว่างติดเว็บไซต์
เดียวภายในไอออนสูงสุดในความแตกต่าง
CS1