PIanta (1982) 154:284-288 Plant, a 9 Springer-Verlag 1982 Variations in ribulose 1,5-bisphosphate carboxylase protein levels, activities and subcellular distribution during photoautotrophic batch culture of Chlorogloeopsis fritschii T. Lanaras and G.A. Codd Department of BiologicalSciences,Universityof Dundee, Dundee DD1 4HN, ILK. Abstract. Ribulose 1,5-bisphosphate (RuBP) carbox- ylase is present in the cytoplasm and carboxysomes (polyhedral bodies) of the cyanobacterium Chloro- gloeopsisfritschii. In vitro enzyme activities have been measured throughout photoautotrophic batch cul- ture, together with RuBP carboxylase protein concen- trations, determined by rocket immunoelectrophore- sis. Enzyme activities and protein levels in the cyto- plasmic and carboxysomal fractions varied in an ap- parently inverse manner during growth. The RuBP carboxylase activities per unit enzyme protein were maximal in late lag phase/early exponential phase for both cellular enzyme pools. Both rates per unit en- zyme protein declined during exponential phase, cyto- plasmic enz3ane activity remaining consistently higher than that of the carboxysomal enzyme. Activities per unit cytoplasmic and carboxysomal enzyme protein showed very low, similar rates in late stationary phase and death phase. Dialysis experiments indicated that such changes were not due to interference in activity assays by soluble endogenous effectors. Major shifts in the subcellular distribution of RuBP carboxylase protein were found versus culture age, enzyme protein levels being predominantly carboxysomal in lag phase, mainly soluble in exponential phase and then mainly carboxysomal again in stationary/death phase. The data are discussed in terms of carboxysome func- tion and the question of control of RuBP carboxylase synthesis in cyanobacteria. Key words: Carboxysome - Chlorogloeopsis - Cyano- bacteria - Polyhedral bodies - Ribulose 1,5-bisphos- phate carboxylase. Introduction D-Ribulose 1,5-bisphosphate (RuBP) carboxylase is present in soluble and particulate cell-free extracts Abbreviations: RuBP =D-ribulose 1,5-bisphosphate; LTIB = low Tris isolation buffer; HTIB=high Tris isolation buffer; RIE= 9 rocket immunoelectrophoresis of cyanobacteria (Codd and Stewart 1976; Badger 1980). The particulate enzyme in Anabaena cylindrica and Chlorogloeopsisfritschii is located in the polyhed- ral bodies (Codd and Stewart t976; Lanaras and Codd 1980, 1981 a), which may thus be termed cyano- bacterial carboxysomes (see Shively 1974; Stewart and Codd 1975). Polyhedral bodies have been found in all cyanobacteria thus far examined (e.g. Fogg et al. 1973; Stewart and Codd 1975; Obukowicz and Ken- nedy 1980; van Eykelenburg 1979). Several chemo- autotrophic bacteria also contain polyhedral bodies and RuBP carboxylase has been shown to be present in those of Thiobacillus neapolitanus (Shively et al. 1973a, 1973b) Nitrobacter agilis (Westphal 1977; Shi- vely et al. 1977) and Nitrosomonas sp. (ttarms et al. 1981). Studies on the relative abundance of soluble (cyto- plasmic) and particulate (carboxysomal) RuBP car- boxylase in cyanobacteria are lacking. Cellular car- boxysome numbers were found to correlate with car- boxysomal RuBP carboxylase activity throughout photoautotrophic batch culture of A. cyIindrica, values being high during the lag and stationary phases and minimal during the early phase of exponential growth (Stewart 1977). It is not known how changes in carboxysomal RuBP carboxylase activity compare with the activity of the soluble enzyme and these have now been studied. We have also measured RuBP carboxylase protein levels in the cytoplasmic and car- boxysomal fractions by rocket immunoelectrophore- sis to examine the subcellular compartmentation of the enzyme during photoautotrophic batch culture of C. fritsehii. Material and methods Organism and growth conditions. Chlorogloeopsis fritschii strain CU t411/Ib (CultureCentre for Algaeand Protozoa,Cambridge,U.K.) was grownphotoautotrophically in Medium C of Kratz and Myers (1955). Cells were grown in t8 dm 3 batch cultures in 20 dm 3 aspi- rators equipped with magneticstirrers. Cultures were maintained at 25 ~ sparged with sterile air at a rate of about 7 dm 3 rain 1, 0032-0935/82/0154/0284/$01.00