Equilibrium binding constants for Tl+ with gramicidins A, B and C in a lysophosphatidylcholine environment determined by 205Tl nuclear magnetic resonance spectroscopy.
Nuclear Magnetic Resonance (NMR) 205Tl spectroscopy has been used to monitor the binding of Tl+ to gramicidins A, B, and C packaged in aqueous dispersions of lysophosphatidylcholine. For 5 mM gramicidin dimer in the presence of 100 mM lysophosphatidylcholine, only approximately 50% or less of the gramicidin appears to be accessible to Tl+. Analysis of the 205Tl chemical shift as a function of Tl+ concentration over the 0.65-50 mM range indicates that only one Tl+ ion can be bound by gramicidin A, B, or C under these experimental conditions. In this system, the Tl+ equilibrium binding constant is 582 +/- 20 M-1 for gramicidin 1949 +/- 100 M-1 for gramicidin B, and 390 +/- 20 M-1 for gramicidin C. Gramicidin B not only binds Tl+ more strongly but it is also in a different conformational state than that of A and C, as shown by Circular Dichroism spectroscopy. The 205Tl NMR technique can now be extended to determinations of binding constants of other cations to gramicidin by competition studies using a 205Tl probe.
Hinton
J F
JF
Koeppe
R E
RE
Shungu
D
D
Whaley
W L
WL
Paczkowski
J A
JA
Millett
F S
FS
D006096:Gramicidin; D007700:Kinetics; D008244:Lysophosphatidylcholines; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D011485:Protein Binding; D013329:Structure-Activity Relationship; D013793:Thallium
D008244:Lysophosphatidylcholines; D006096:Gramicidin; D013793:Thallium