A circadian rhythm of the luciferin binding protein fromGonyaulax polyedra

It has previously been shown that a protein extracted fromGonyaulax polyedra strongly and specifically binds luciferin, the substrate of the bioluminescent reaction. This binding is markedly dependent on pH with tight binding at pH 8.0 and almost no binding at pH 6.5, as measured by two independent methods. A procedure for the determination of the dissociation constant (Kd) of the luciferin binding protein (LBP) is presented, and Kd is estimated to be7×10−9 M at pH 8.0, assuming an overall quantum yield of 0.1 for the bioluminescent reaction. With cells grown in a 12 h light — 12 h dark cycle, 5 to 10 times more LBP activity can be extracted from dark phase cells than from light phase cells. This rhythm persists in a circadian fashion in cultures maintained in constant dim light.