The solution conformations of pyridoxal-5′ -phosphate and pyridoxamine-5′-phosphate have been investigated using Eu(III) as a nuclear magnetic resonance shift probe. Binding of Eu(III) to pyridoxal phosphate results in the formation of two complexes, at the phosphate group and theo-hydroxy-aldehyde moiety, which are in slow exchange on the nuclear magnetic resonance time-scale. The lanthanide-induced pseudo contact shifts calculated using the McConnell-Robertson equation (J. Chem. Soc. (1950), 22, 1561) are in good agreement with the experimentally observed values for both pyridoxal phosphate and pyridoxamine phosphate and lead to a family of closely related conformations.

The binding ofRicinus communis agglutinin andAbrus agglutinin to 4-methylumbelliferyl β-D-galactopyranoside was studied by equilibrium dialysis, fluo-rescence quenching and fluorescence polarization. The number of binding sites and the association constant value obtained by fluorescence polarization for bothRicinus communis agglutinin andAbrus agglutinin are in close agreement with those obtained by the other methods. This indicates the potential of ligand-fluorescence polarization measurements in the investigation of lectin-sugar interactions.

Alamethicin and related α-aminoisobutyric acid peptides form transmembrane channels across lipid bilayers. This article briefly reviews studies on the effect of alamethicin on lipid phase transitions in lipid bilayers and on mitochondrial oxidative phosphorylation. Fluorescence polarization studies, employing 1,6-diphenyl-1,3,5-hexatriene as a probe, suggest that alamethicin fluidizes lipid bilayers below the phase transition t-emperature, but has little effect above the gel-liquid crystal transition point. Alamethicin is shown to function as an uncoupler of oxidative phosphorylation in rat liver mitochondria. The influence of alamethicin on mitochondrial respiration is modulated by the phosphate ion concentration in the medium. Classical uncoupling activity is evident at low phosphate levels while inhibitory effects set in at higher phosphate concentrations. Time-dependent changes in respiration rates following peptide addition are rationalized in terms of alamethicin interactions with mitochondrial membrane components.

The interactions of symmetrical alkyldiamines with bilirubin-IX α have been examined in dichloromethane and dioxane solutions, by visible region difference sPectroscoPy and florescence methods. In dioxane solutions a clear difference is observed between the comPlexes of the shorter chain diamines (number of sPacer methylene grouPs (n ≤4) ) and the longer chain diamines (n ≥6) . The variations in sPectral features with diamine chain length are less Pronounced in dichloromethane. The sPectroscoPic results are consistent with the occurrence of distinct bilirubin conformations dePending uPon the solvent and the geometry of the interacting recePtor. Based on molecular modelling two conformations are ProPosed. A ‘ridge-tile’ model similar to that observed in crystals is favoured for binding to the longer diamines, while a ‘quasi-cyclic’ structure is Preferred for interaction with the short chain diamines.