Transition Moments Of Chromophores Research Articles

The novel behaviour of interactions between Ni2+ ion and human or bovine serum albumin

We discovered a series of novel behaviours of interactions between Ni2+ ion and human or bovine serum albumin. Our results indicated that there exist two closely neighbouring identical prior binding sites in the binding of human or bovine serum albumin with Ni2+ ions, not only one. It is very likely that, after the binding of the first Ni2+ ion, an induced slow conformational transition happens, which leads to the binding of the second Ni2+ ion and shows itself as a hysteretic effect for a process of non-enzymic protein binding with metal ions. As the concentrations of the 1:1 (molar ratio of Ni2+ ion to protein) system increase, an increasing hypochromic effect is observed. Such a hypochromic effect has not been reported previously; however, it is in accord with the mechanism of dipole-dipole interactions between the electric dipole transition moments of chromophores.

Orientation of the chromophore transition moment in the 4-leaved shape model for pea phytochrome molecule in the red-light absorbing form and its rotation induced by the phototransformation to the far-red-light absorbing form

Orientation of the chromophore transition moment in pea phytochrome (subunit molecular mass, 114 kDa) in the red-light-absorbing form (P r) and its rotation induced by the phototransformation to the far-red-light-absorbing (P fr) form was studied by measuring linear dichroism of oriented phytochrome prepared by a ‘gel squeezing method’. The phytochrome in P r showed a negative linear dichroism. On the contrary, the P fr form showed positive linear dichroism. Assuming that the molecular axis for the two-fold rotational symmetry in the ‘4-leaved shape model’ proposed recently for the dimeric molecular structure of the phytochrome [(1989) FEBS Lett. 247, 139–142], is oriented in parallel with the direction of the external constraint, the average azimuthal angle between the molecular axis and the transition moment of the chromophore was calculated as 59° or 121° for P r and 52° or 128° for P fr. These results explain well the polarotropic responses by phytochrome observed in plant organisms.

Angle of the retinal of bacteriorhodopsin in blue membrane

The electric dichroism of purple and cation-depleted (blue) membrane was measured in a.c. electric fields at saturation. A decrease of 5.5 degrees in the direction of the chromophore transition moment with respect to the membrane normal was found upon removal of cations from purple membrane.

Electric Linear Dichroism Study of Sodium Poly(p-styrenesulfonate) and Its 9-Aminoacridinium Complex in Aqueous Solutions

Abstract Electric linear dichroism (ELD) of sodium poly(p-styrenesulfonate) (NaPSS) and its 9-aminoacridinium (AA) complex at a mixing ratio of polymer residue-to-dye of 6.14 was studied in aqueous solutions at 20 °C. ELD signals were measured in the electric field strength range 0—ca. 19 kV/cm at the absorption peak wavelengths; they showed a saturating trend at extremely high fields. The average angles between the orientation axis of NaPSS and the transition moments of chromophores were estimated to be 60° at 224.5 nm and 57° at 262 nm for the side chain phenyl group and 50° at 404 nm for the bound AA by using theoretical orientation functions derived for mono- and polydisperse systems. The ELD spectra were measured at fixed field strengths; 275–215 nm for NaPSS and 440–282 nm for NaPSS–AA. The reduced dichroism of NaPSS remained nearly constant throughout the 262 nm band but steadily changed below 224 nm in the 224.5 nm band, indicating that another band exists in the far UV region. The ELD spectrum of the NaPSS–AA complex revealed that the two electronic 1La and 1Lb transition moments of the bound AA are tilted at different angles to the orientation axis of the NaPSS backbone.

Three-dimensional crystals of membrane proteins: bacteriorhodopsin.

The intrinsic membrane protein bacteriorhodopsin has been crystallized by salt precipitation after solubilization by octyl glucoside. Two different crystal forms were obtained, depending on the nature of the salt used and the pH. Needles formed in the presence of sodium phosphate and in ammonium sulfate solutions above pH 4.8. Cubes appeared in sodium citrate solutions or ammonium sulfate. Unlike the cubic crystals, the birefringent needles showed strong linear dichroism, which allowed determination of the orientation of the chromophore's transition moment. The procedure described here may be of general use in crystallographic studies of membrane proteins.

Plane-polarized light in microspectrophotometry

Theoretical analysis permits the description of absorptive interaction between plane-polarized light and visual pigment in single, side-illuminated, vertebrate photoreceptors. The distribution of light in the aperture cone of the microscope condenser and the distribution of chromophore transition moment in the cylindrical cell are to produce two components of absorption: in the direction of propagation as well as in the plane of polarization. Measured dichroic ratio is precisely interpreted in terms of axial extinction and condenser aperture. The accuracy of the former is analyzed as a function of the latter parameter. Numerical aperture size selection is discussed.