Biosynthesis of ribulose-1.5-bisphosphate carboxylase in greening cells of Euglena gracilis

Light induction of chloroplast development in Euglena leads to quantitative changes in the protein composition of the soluble cell part. One major part of these is the observed accumulation of ribulose-1.5-bisphosphate carboxylase/oxygenase (RuBPCase) enzyme (EC 4.1.1.39). As measured by immunoelectrophoresis, a small amount of RuBPCase (about 10^-6 pmol) is present in a dark-grown cell, whereas a greening cell (72h) contains 10–20 pmol enzyme. Both the cytoplasmic and chloroplastic translation inhibitors, cycloheximide and spectinomycin, have a strong inhibitory effect on the synthesis of the enzyme throughout the greening process of Euglena cells. Electrophoretic and immunological analyses of the soluble phase prepared from etiolated or greening cells do not show the presence of free subunits of the enzyme. For each antibiotic-treated greening cell, the syntheses of both subunits are blocked. Our data indicate that tight reciprocal control between the syntheses of the two classes of subunits occurs in Euglena. In particular, the RuBPCase small subunit synthesis in greening Euglena seems more dependent on the protein synthesis activity of the chloroplast than the syntheses of other stromal proteins from cytoplasmic origin.Abbreviations LSU large subunit of ribulose-1.5-bisphosphate carboxylase - RuBP ribulose-1.5-bisphosphate - RuBP-Case ribulose-1.5-bisphosphate carboxylase - SSU small subunit of ribulose-1.5-bisphosphate carboxylase