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Articles

Ribulose Bisphosphate Carboxylase from Three Chlorophyll c-Containing Algae ¹

Physical and Immunological Characterizations

Botany Department, University of Georgia, Athens, Georgia 30602, Microbiology Department, University of Georgia, Athens, Georgia 30602

Distinctive properties are identified in the molecular structure of ribulose, 1,5-bisphosphate carboxylase/oxygenase (RuBPCase) in chlorophyll c-containing algae (i.e., chromophytes). Using purified enzyme from Cryptomonas sp., Coccolithophora sp., and Cylindrotheca fusiformis, we have determined that the RuBPCase holoenzyme of each species has a molecular weight, subunit composition, and isoelectric points of its subunits similar to the purified enzymes from pea and Chlamydomonas reinhardtii. The large subunits from chromophytes exhibit microheterogeneity in their isoelectric points, whereas two to four well-resolved isoelectric variants of the small subunit were observed in each RuBPCase preparation. In spite of the high degree of similarity in terms of physical properties, both the small and large RuBPCase subunits of the chromophytes are structurally different from those of chlorophytes; immunological studies demonstrate that RuBPCase subunits of these two groups have few antigenic determinants in common.

¹ Supported by Department of Energy grant DE-FG02-84ER 13188 to GWS. D. L. K. was supported by National Science Foundation grants BSR 8215587 and OCE 8117834 to R. E. H.