Cadmium-induced luminescence of recombinant photoprotein obelin

AbstractIt has been shown for the first time that Cd2+ ions induce substantial bioluminescence of a Ca2+-binding photoprotein: recombinant obelin. The optimum pH for the bioluminescent reaction in the presence of Cd2+ ions is pH 6. The intensity, L, of the light emission for the Cd2+ ions is 75% of the intensity of the signal in the presence of Ca2+. The quantum yields of the reactions in the presence of Cd2+ and Ca2+ are 0.18 and 0.24 respectively. The slope of the straight line (between 5 and 90% of Lmax in the coordinates of log(L(Lmax-L)) vs. log([Cd2+]) is 1.75 ± 0.06, which indicates positive cooperative character of this reaction. At a concentration exceeding 1 · 10−3 M, Cd2+ inhibits the bioluminescent reaction