Possibility of a Double Well Potential in the Proton Bridge of Visual Pigments and Bacteriorhodopsin

The resonance Raman effect is examined in the case of vibrations which are governed by a double well potential. It is shown that in such a case the intensity of a resonance Raman line depends on three factors: the relative populations of the two wells in the . ground state and in the resonating electronic excited state and the displacement of the potential minima between the ground state and the excited state. Depending on the shapes of the potentials in the two states, the ground state populations might become unimportant as a factor determining intensities and the only observed Raman line might be due to the less populated well. It is suggested that such a situation is likely to exist for the proton bridge of the chromophore of visual pigments and bacteriorhodopsin, the Schiff bases of 11-cis and all-trans retinals respectively. This raises the question if resonance Raman spectra alone are capable of giving evidence of the extent of protonation of the chromophore in the ground state

Recognition of Anesthetic Barbiturates by a Protein Binding Site: A High Resolution Structural Analysis

Barbiturates potentiate GABA actions at the GABAA receptor and act as central nervous system depressants that can induce effects ranging from sedation to general anesthesia. No structural information has been available about how barbiturates are recognized by their protein targets. For this reason, we tested whether these drugs were able to bind specifically to horse spleen apoferritin, a model protein that has previously been shown to bind many anesthetic agents with affinities that are closely correlated with anesthetic potency. Thiopental, pentobarbital, and phenobarbital were all found to bind to apoferritin with affinities ranging from 10–500 µM, approximately matching the concentrations required to produce anesthetic and GABAergic responses. X-ray crystal structures were determined for the complexes of apoferritin with thiopental and pentobarbital at resolutions of 1.9 and 2.0 Å, respectively. These structures reveal that the barbiturates bind to a cavity in the apoferritin shell that also binds haloalkanes, halogenated ethers, and propofol. Unlike these other general anesthetics, however, which rely entirely upon van der Waals interactions and the hydrophobic effect for recognition, the barbiturates are recognized in the apoferritin site using a mixture of both polar and nonpolar interactions. These results suggest that any protein binding site that is able to recognize and respond to the chemically and structurally diverse set of compounds used as general anesthetics is likely to include a versatile mixture of both polar and hydrophobic elements

INFRARED SPECTRA OF SIMPLE AMINES AND THEIR IONS

Author Institution: Institut d\'e Chimic, Universit\'e de Montr\'ealA preliminary account is given of a comparative study of infrared spectra of simple amines and their chlorohydrates. Primary, secondary, and tertiary amines and their respective ions are studied,-- aliphatic, aromatic and aza-compounds -- and a general view on these spectra is sought. The effect of lonization on the amino-groups is discussed on the basis of the NH stretching and bending bands. Other bands in the spectra give information on modifications in the structure of the hydrocarbon part of these molecules following ionization. All the amines and ions were examined in various media: liquid or solid, aqueous solutions if possible, and solution of the hydrochlorides in their own amines or other amines when the latter are liquids. Relations between spectra taken in these media change in a significant manner for different types of compounds. The results are compared with known ultraviolet data