Conformational analysis of erythrosine B (FD&C Red No. 3) and its comparison with thyroid hormone structures

Deiodinases control local cellular and systemic thyroid hormone availability

Iodothyronine deiodinases (DIO) are a family of selenoproteins controlling systemic and local availability of the major thyroid hormone l-thyroxine (T4), a prohormone secreted by the thyroid gland. T4 is activated to the active 3,3'-5-triiodothyronine (T3) by two 5'-deiodinases, DIO1 and DIO2. DIO3, a 5-deiodinase selenoenzyme inactivates both the prohormone T4 and its active form T3. DIOs show species-specific different patterns of temporo-spatial expression, regulation and function and exhibit different mechanisms of reaction and inhibitor sensitivities. The main regulators of DIO expression and function are the thyroid hormone status, several growth factors, cytokines and altered pathophysiological conditions. Selenium (Se) status has a modest impact on DIO expression and translation. DIOs rank high in the priority of selenium supply to various selenoproteins; thus, their function is impaired only during severe selenium deficiency. DIO variants, polymorphisms, SNPs and rare mutations have been identified. Development of DIO isozyme selective drugs is ongoing. A first X-ray structure has been reported for DIO3. This review focusses on the biochemical characteristics and reaction mechanisms, the relationships between DIO selenoproteins and their importance for local and systemic provision of the active hormone T3. Nutritional, pharmacological, and environmental factors and inhibitors, such as endocrine disruptors, impact DIO functions.

Molecular mobility and dynamic site heterogeneity in amorphous lactose and lactitol from erythrosin B phosphorescence

We have used phosphorescence from erythrosin B to characterize the molecular mobility and dynamic heterogeneity in dry films of amorphous lactose and lactitol from -25 to 120 degrees C. The phosphorescence emission spectra red-shifted and broadened with temperature in both sugars, indicating that both the rate of dipolar relaxation and the extent of inhomogeneous broadening increased dramatically at higher temperature. Phosphorescence intensity decays were well fit using a stretched exponential decay model; the rate constant for non-radiative quenching due to collisions with the matrix was calculated from the lifetimes. Arrhenius plots of this rate were non-linear, increasing very gradually at low and dramatically at high temperatures in both sugars. The rate of quenching was significantly lower in a 1:1 (wt/wt) mixture of lactose/lactitol in both the glass and the melt, providing strong evidence that specific interactions within the mixture lowered the matrix mobility. The lifetimes varied systematically with emission wavelength in both matrixes; analysis of the temperature dependence indicated that the activation energy for non-radiative quenching of the triplet state varied somewhat with emission wavelength. Time-resolved emission spectra collected as a function of delay time following pulsed excitation exhibited significant shifts to higher energy as a function of time. These data support a photophysical model in which erythrosin B molecules are distributed among matrix sites that vary such that blue-emitting sites with slower rates of matrix dipolar relaxation also have slower rates of molecular collisions. The amorphous matrixes of lactose and lactitol in both the glass and the melt state are thus characterized by dynamic site heterogeneity in which different sites vary in terms of their overall molecular mobility.

Dynamic site heterogeneity in amorphous maltose and maltitol from spectral heterogeneity in erythrosin B phosphorescence

We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in thin films of either maltose or maltitol to investigate the physical properties of these amorphous pure sugar matrixes. Intensity decays collected as a function of emission wavelength over the range from 640 to 720 nm were analyzed using a stretched exponential kinetic model in which the lifetime (tau) and the stretching exponent (beta) were the physically relevant parameters. The lifetimes varied systematically with emission wavelength in both matrixes. Analysis of the temperature dependence of the lifetime at each wavelength provided an estimate of the activation energy for nonradiative quenching of the triplet state; the activation energy also varied with emission wavelength. In addition, time-resolved emission spectra exhibited a blue shift with time following excitation. These data support a photophysical model in which probes are distributed among sites that vary in terms of overall molecular mobility and in which sites with lower rates of dipolar relaxation also have lower rates of collisional quenching of the erythrosin triplet state. The amorphous matrix of both maltose and maltitol in both the glass and the melt state is thus characterized by dynamic site heterogeneity in which different sites vary in terms of their overall molecular mobility.