The effect of decreased oxygen concentration on photosynthetic biomass production was determined for Euglena gracilis Klebs strain z and Chlamydomonas reinhardtii Dangeard. At a constant carbon dioxide concentration of 0.03% (v/v), decreasing the oxygen concentration from 21% to 2% (v/v) gave a two-fold increase in dry-weight yield for E. gracilis; a result consistent with the operation of a functional glycollate pathway in this alga. A similar effect of oxygen concentration on dry-weight yield was not observed with C. reinhardtii.

Regreening cultures were transferred back into darkness after harvesting the cells by centrifugation and resuspending them in an equivalent volume of Hutner's medium (15).Inhibitors were dissolved in the appropriate culture medium and sterilized by Seitz filtration before being added to cultures at times indicated under "Results."Inhibitors. The D-threo-isomer of chloramphenicol was used exclusively throughout this work (8). The final concentration of inhibitors used was D-threo-chloramphenicol, 1 mg/ml; cyclohemixide, 15 ,g/ml; 5-fluorouracil, 5 mm; rifampicin, 250 ,ug/ml. NaH'4C03 into acid-stable product was determined exactly as described previously (21). RESULTS AND DISCUSSIONEuglena RuDPCase has been recently purified and characterized (22). This enzyme has the high mol wt and distinctive quaternary structure which is typical for this enzyme isolated from higher plants and green algae (11,16,18,20,27). In the presence of sodium dodecyl sulfate, the enzyme dissociates into two nonidentical subunits of mol wt 55,000 and 15,000; eight 600 www.plantphysiol.org on May 9, 2018 -Published by Downloaded from

Ribulose 1,5-diphosphate carboxylase was isolated from Euglena gracilis Klebs strain Z Pringsheim, Chlorella fusca var. vacuolata, and Chlamydobotrys stellata, and the subunits from each enzyme were separated and purified by gel filtration on Ribulose 1,5-diphosphate carboxylase, the enzyme that catalyzes CO2 fixation in photosynthetic and chemosynthetic organisms (15), has recently been purified from the green algae Euglena gracilis (16,20), Chlamydomonas reinhardtii (4), Chlorella sps (10, 23), and Chlamydobotrys stellata (17). In the presence of SDS, the enzyme from algae dissociates into two nonidentical subunits of mol wt 55,000 and 15,000, eight large and eight small subunits constituting the multimeric enzyme (16). Inhibitor studies with Euglena (3, 11) support current concepts regarding the synthesis of RuDP Case2 in eukaryotic cells (2,8) that the larger subunit is coded for by chloroplast DNA and synthesized on 68S chloroplast ribosomes, while the small subunit is coded for by nuclear DNA and synthesized on 87S cytoplasmic ribosomes. The regulation of biosynthesis and assembly of such multimeric proteins over the Euglena cell cycle has been little investigated. Preliminary experiments with regreening Euglena cultures suggest that under these conditions, the synthesis of RuDP Case subunits may not be in synchrony (11,12). Further progress is dependent on methods for detecting nascent RuDP Case subunits, and with this objective in view, we have produced antibodies to Euglena RuDP Case subunits and determined their specificity. These antibodies have also been used to determine serological affinity between isolated subunits of RuDP Case from green algae.