Abstract
Addition of calcium tons to the Ca2+-regulated photoproteins, such its aequorin and obelin, produces it blue bioluminescence originating from fluorescence transition of the protein-bound product coelenteramide. The kinetics of several transient fluorescent species of the bound coelenteramide is resolved after picosecond-laser excitation and streak camera detection. The Initially formed spectral distributions at picosecond-times are broad, evidently comprised of two contributions, One at higher energy (similar to 25 000 cm(-1)) assigned as from the Ca2+-discharged photoprotein-bound coelenteramide in its neutral state. This component decays much more rapidly (t(1/2) similar to 2 ps) in the case of the Ca2+-discharged obelin than aequorin (t(1/2) similar to 30 ps). The Second component at lower energy shows several intermediates in the 150-500 ps miles. with it Final species having spectral maxima 19 400 cm(-1), bound to Ca2+-discharged obelin. and 2 1300 cm(-1), bound to Ca2+-discharged aequorin, and both have it fluorescence decay lifetime of 4 ns It is proposed that the rapid kinetics of these fluorescence transients oil the picosecond time scale, correspond to times For relaxation of the protein Structural environment of the binding cavity