Recognition sites structure

Cholanic acid also possesses the ability of transporting cations across a lipophilic membrane but the selectivity is not observed because it contains no recognition sites for specific cations. In the basic region, monensin forms a lipophilic complex with Na+, which is the counter ion of the carboxylate, by taking a pseudo-cyclic structure based on the effective coordination of the polyether moiety. The lipophilic complex taken up in the liquid membrane is transferred to the active region by diffusion. In the acidic region, the sodium cation is released by the neutralization reaction. The cycle is completed by the reverse transport of the free carboxylic ionophore. 

Fig. I. Structure of the model compound. R and R represent the recognition sites.----, Hydrogen bonding...

By structural complementarity, dicationic l,4-diazabicyclo[2.2.2]octane (VII) provides an appropriate recognition site for phosphate ions and two stearyl side chains attached to the amines add lipophilic properties 59,60). Such a carrier model can selectively extract nucleotides from aqueous solution to chloroform solution via lipophilic salt formation. The order of nucleotide affinity is ATP > ADP > AMP. The selectivity ratios were 45 for ADP/AMP and 7500 for ATP/AMP at pH 3. The relative transport rate was ATP > ADP > AMP. The ratios were 60 for ATP/AMP and 51 for ADP/AMP. The modes of interaction of ADP and ATP are proposed to be as shown in Fig. 6. 

The formation of such complexes apparently involves a delicate balance of binding forces, since a-phenyl-ethylamine 30 shows only modest tendencies to form 2 1 complexes and its stacking efficiency is reduced. The structural details of these complexes are not known, but intermoleeular NOE experiments favor structures such as shown in 31. The distance between the aromatic and amine recognition sites in the... 

Mash, D.C. and Staley, J.K. Cocaine recognition sites on the human dopamine transporter in drug overdose victims. In Neurotransmitter Transporter Structure and Function, Reith, M.E.A., Ed. Humana, New York, 1996, 56. 

Van Regenmortel, M. H. V. (1999c), Molecular design versus empirical discovery in peptide-based vaccines. Coming to terms with fuzzy recognition sites and ill-defined structure-function relationships in immunology , Vaccine, 18, 216-221. 

Lo Conte, L., Chothia, C and Janin, J. (1999) The atomic structure of protein-protein recognition sites../. Mol. Biol. 285,2177-2198. 

---