Kinetics of Accumulation of Ribulose-1,5-bisphosphate Carboxylase during Greening in Euglena gracilis: Photoregulation.

The preparation of a rabbit antibody to ribulose-1,5-bisphosphate carboxylase (RuBPCase) from Euglena gracilis and its use to quantitate RuBPCase in dark- and light-grown cells and during light-induced chloroplast development (greening) are described. Light-grown Euglena have at least 36 times more RuBPCase than dark-grown Euglena. Light is required for both the initiation and continued increase in net synthesis of RuBPCase over the dark level: brief illumination 12 hours before exposure to continuous light eliminates the lags in the accumulation and increase in activity of RuBPCase (as well as in chlorophyll accumulation); net synthesis is blocked in greening cells returned to the dark or exposed to 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Streptomycin or cycloheximide prevents RuBPCase accumulation when added at the beginning of greening but only partially blocks accumulation when added after 25 hours of greening. After 24 hours of greening, the activity of RuBPCase per milligram chlorophyll continues to increase slowly while concentration of the enzyme per milligram chlorophyll remains constant. This increased activity may be due to activation of the enzyme as well as to net synthesis.