Location of third binding-site

Fig. 12.—Location" of the Third Binding-site in Nitroanilines (X), Sugars (-y), and Dipeptide Sweeteners (S). [Distances given in pm.]...

In the 70 S initiation complex, formylme-thionine tRNA is initially located at a binding site known as the peptidyl site (P). A second binding site, the acceptor site (A), is not yet occupied during this phase of translation. Sometimes, a third tRNA binding site is defined as an exit site (E), from which uncharged tRNAs leave the ribosome again (see p. 252 not shown). 

Based on the amino acid sequence determined by Behrens et al. (37) and Meloun et al. (38) and the identity of the diisopropylfluoro-phosphate reactive residue (39), we tentatively have located the tryptophan binding site in the carboxyl terminal third of HSA including or adjacent to tyrosine 411 (34). However Gambhir et al. (40) previously have identified a histidine residue near the amino terminal end of the sequence as being in that site. The conformation of HSA may be such that both residues are in that site however other explanations are also possible. 

Dodd, J. R. and Christie, D. L. (2001) Cysteine 144 in the third transmembrane domain of the creatine transporter is located close to a substrate-binding site.. /. Biol. Chem. 276, 46983-46988. 

The EPR spectral data indicated that two cyanide anions bind to copper at low temperature where two cyanide anions and two histidines are present in the basal plane and the third histidine residue is present in the axial position. It has been proposed that the second cyanide anion displaces the coordinated water. Similarly, it has been proposed that the oxalate anion coordinated in a bidentate fashion and displaced the coordinated water. In case of sulfonamides, the coordination geometry is reported to be the same as that of ZnCa. 13C NMR spectroscopy was used to explore the location of C02 and HCO3 with respect to metal ion in CuCa (129,130,138). It indicated that HCO3 is bound directly to Cu (137). The affinity constant of C02 for CuCa is <1 M-1 but the paramagnetic effect is paradoxically high (130). These results indicated that C02 does not bind to a specific site but probably is attracted by the cavity either by hydrophobic interactions or by the metal ion or by both. 

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