Fig. 4.

Effect of the presence of exogenous protochlorophyllide on cyclase activity. P (28 μg of protein) and S (140 μg of protein) were set up under standard assay conditions, with various concentrations of protochlorophyllide. One set of samples was quenched at time zero, and the protochlorophyllide extracted was quantitated (▴). The second set of samples was incubated for 20 min, and the protochlorophyllide present in these samples is indicated (▪). The cyclase activity at each concentration of added protochlorophyllide is the difference between the zero time and incubated samples. At all protochlorophyllide concentrations, this difference was ≈230 pmol of protochlorophyllide per mg of protein for every 20-min period.