Chemistry of photoproteins as interface between bioactive molecules and protein function

Abstract

Bioluminescence of Okinawan squid includes a photoprotein named "Symplectin" which gives light by addition of Na+ (or K+). The chromophore is covalently bound-imidazopyrazinone analog to protein. Symplectin was extracted with 0.6M KCl and was analyzed to be composed of 3 different molecular-size proteins. Symplectin A, the smallest photoproteins, was purified by gel permeation chromatography to have 15kd by MALDI/TOF mass spectrometry. The molecular mechanism of this luminescence is described. Bioluminescence is also applied for trace analyses and the chromophore in some new fireflies is chemically analyzed. We made a very sensitive detection system of luciferin to a detection limit of 10-16 mol/10μl by using immobilized luciferase and a single photon-counter. An example of the firefly luminescence application is demonstrated in an inhibitory-assay of protein phosphatase activity by inhibitors in the same class of tautomycin/okadaic acid.