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

The accumulation of ribulose-1,5-bisphosphate carboxylase (RuBPCase) in resting Euglena gracilis strain Z during greening is photo-regulated (Freyssinet, Eichholz, Buetow 1984 Plant Physiol 75: 850-857. Greening resting cells are not photosynthetically competent for about the first 24 hours in the light. Therefore, substrates for a net synthesis of the enzyme must come from endogenous constituents. During this time, degradation of endogenous paramylum (carbohydrate) reserves provides the main source of substrates. By about 24 hours of greening, resting cells are photosynthetically competent and RuBPCase accumulation becomes highly sensitive to 3-(3,4 dichlorophenyl)-1,1-dimethylurea. Therefore, from about 24 hours of greening onward, substrates (and/or energy) for RuBPCase synthesis are provided by photosynthesis. Ethanol, a nutritional substrate ordinarily used constitutively by Euglena for growth, inhibits RuBPCase accumulation when added to the resting medium in the light. The alcohol exerts this negative regulatory effect by limiting the availability of substrates needed for a net synthesis of the enzyme.