quin-2

(2-[(2-bis-[carboxymethyl]aono-5-methoxyphenyl)-methyl-6- methoxy-8-bis[carboxymethyl]aminoquinoline); a fluorescent compound that binds Ca⁺⁺ tightly. The wavelengths of light that cause fluorescence when Ca⁺⁺ is bound are longer than the wavelengths that cause fluorescence when Ca⁺⁺ is not bound. When excited at two different wavelengths, the ratio of the fluorescence intensities at the two wavelengths gives the ratio of the concentrations of bound to free Ca⁺⁺. Free q. concentration can be measured precisely, so free Ca⁺⁺ concentration can be calculated precisely. Q. may be injected into cells to measure moment-to-moment changes in intracellular Ca⁺⁺ concentration. SEE ALSO: aequorin, fura-2.