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Biophysical studies of membrane proteins/peptides. Interaction with ...

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[ 1+<br />

(2 / π)arcsin(<br />

R'<br />

/ 2R<br />

)]<br />

BINDING OF A QUINOLONE ANTIBIOTIC TO BACTERIAL<br />

PORIN OmpF<br />

⎧<br />

p<br />

R'<br />

⎪<br />

0 < R'<br />

< 2R<br />

'2 2<br />

p<br />

⎪<br />

Rd<br />

− Rp<br />

W ( R'<br />

) = ⎨<br />

(A4)<br />

⎪ 2R'<br />

⎪<br />

'2 2<br />

2Rp<br />

< R'<br />

< R'<br />

d<br />

⎪⎩<br />

Rd<br />

− Rp<br />

Note that, whereas for R’ > 2R p (where R p is the cylindrical protein radius)<br />

W(R’) is as expected for a uniform distribution <strong>of</strong> acceptors in a planar disk (only<br />

corrected in the denominator for the excluded area resulting from the existence <strong>of</strong> a<br />

protein molecule inside R d ), for R’ < 2R p the more complex expression denotes that only<br />

a fraction <strong>of</strong> the region between R’ and R’ + dR is available to acceptors (the shaded<br />

area in Fig. A1B). Insertion <strong>of</strong> this distribution function in the definition <strong>of</strong> J(t) (the<br />

integral in Eq. A1), together <strong>with</strong> the substitution α = cosθ = w/R, leads to<br />

⎡<br />

2 1<br />

6<br />

2w<br />

⎛ t ⎞⎛<br />

R0<br />

⎞ 6<br />

−3<br />

J ( t)<br />

= ∫ exp⎢<br />

⎜−<br />

⎟⎜<br />

⎟ α ⎥ f ( α)<br />

α dα<br />

(A5)<br />

'2 2<br />

Rd<br />

− R<br />

p + ⎢⎣<br />

⎝ τ<br />

2 ' 2 ⎠⎝<br />

⎠<br />

w / w R D<br />

w<br />

d<br />

⎥⎦<br />

⎤<br />

where<br />

⎧<br />

⎪<br />

w<br />

w<br />

⎪<br />

1<br />

< α <<br />

2 '2<br />

2 2<br />

w + Rd<br />

w + 4Rp<br />

⎪<br />

f ( α)<br />

= ⎨<br />

(A6)<br />

⎪<br />

w<br />

⎪ ⎛<br />

2<br />

1 1<br />

⎞<br />

< α <<br />

⎪<br />

⎜ w 1− α<br />

1<br />

+ arcsin ⎟<br />

2 2<br />

+<br />

π ⎜ ⎟<br />

w 4Rp<br />

2<br />

⎩ ⎝<br />

2αRp<br />

⎠<br />

We now rearrange Eq. A5 into<br />

123

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