Ruthenium red as a resonance Raman probe of Ca2+ binding sites in biological materials

The binding of Ruthenium red to tubulin

The inhibition of microtubule assembly by Ruthenium red (Deinum, J., Wallin, M., Kanje, M. and Lagercrantz, C. (1981) Biochim. Biophys. Acta 675, 209-213) could be counteracted by either taxol or dimethyl sulfoxide. Ruthenium red remained bound to the assembled microtubules. Microtubules assembled in the presence of Ruthenium red and taxol showed the typical taxol-dependent stability. The dimethyl sulfoxide-induced microtubules showed normal assembly characteristics, e.g., were GTP dependent, could be disassembled by cold, colchicine and Ca2+ and had no alterations in ultrastructure. The absolute disassembly induced by Ca2+ in the presence of dimethyl sulfoxide and Ruthenium red was dependent on the microtubule protein concentration, but independent in the absence of Ruthenium red. Ruthenium red was strongly bound to purified tubulin also in the presence of 8% (v/v) dimethyl sulfoxide. The dimethyl sulfoxide-induced assembly of purified tubulin in the presence of Ruthenium red was slightly stimulated, although the critical protein concentration was the same. It was found by resonance Raman spectroscopy with a flow technique that Ruthenium red did not bind to a specific calcium binding site on tubulin, although binding to a GTP binding site cannot be excluded. The wavenumbers of the lines in the region 375-500 cm-1 differ from those found for Ruthenium red bound to typical calcium-binding proteins such as calmodulin. Although Ruthenium red binds to serum albumin as well, the spectrum with albumin resembled that of the free dye.

Passive membrane permeability to small molecules and ions in transformed mammalian cells: probable role of surface phosphorylation

Addition of ATP to medium surrounding intact, transformed 3T3 cells causes the formation of aqueous channels in the plasma membrane. This effect of extracellular ATP is sharply dependent on the pH and temperature of the incubation medium, and is inhibited by low levels of La3+ or ruthenium red; inhibition is also obtained with concentrations of Mg2+ ions that exceed a ratio of Mg/ATP of one. The effect of ATP on membrane channel formation is unaffected by chelators of metal ions or by prior modification of the cell surface with various surface-active enzymes or sulfhydryl reagents. Under conditions which favor aqueous channel formation, incubation of intact 3T6 cells with ATP (gamma-32P) leads to phosphorylation of two membrane components with apparent molecular weight of 40,000 (40K) and 110,000 (110K) daltons; the 110K component which is unaffected by trypsin under normal conditions is rendered trypsin-sensitive by the phosphorylation reaction, probably as a result of a conformational change. Conditions which inhibit aqueous channel formation also inhibit phosphorylation of the 110K protein and decrease the labeling of the 40K component. These results indicate the probable role of cell surface phosphorylation, involving one or both of these components, in the formation of aqueous channels in transformed 3T3 cells. Aqueous channel formation by extracellular ATP is not associated with gross unfolding of the cell surface as revealed by lactoperoxidase-catalyzed iodination of the 3T6 cell surface.

X-ray structure of [Ru3 O2 (NH3)14]6+, cation of the cytological reagent Ruthenium Red

The X-ray crystal structure of [Ru3 O2 (NH3)14] (S2 O3)3 . 4H2 O, the thiosulphate salt of Ruthenium Red, has been determined. The cation contains an essentially linear N-Ru-O-Ru-O-Ru-N backbone formed from three ruthenium coordination octahedra, giving an effectively cylindrical shape to the ion. Resonance Raman spectra are consistent with retention of this structure in solution.