Variations in Kinetic Properties of Ribulose-1,5-bisphosphate Carboxylases among Plants

Abstract

Studies of ribulose-1,5-bisphosphate (RuBP) carboxylase taxonomically diverse plants [Casuarina, Clematis, Fragaria, Fissidens, Ilex, Ginkge, Kalanchos spp. Macrozania, Selaginella, Magnolia, Rumex, Pellaea, Populis, Pinus and Pteridium] show that the enzyme from C2 and crassulacean acid metabolism pathway species exhibits lower Km (CO2) values (12-25 .mu.M) than does that from C4 species (28-34 .mu.M). RuBP carboxylase from aquatic angiosperms, an aquatic bryophyte, fresh water and marine algae has yielded consistently high Km (CO2) values (30-70 .mu.M), similar in range to that of the enzyme from C4 terrestrial plants. This variation in Km (CO2) is discussed in relation to the correlation between the existence of CO2-concentrating mechanisms for photosynthesis and the affinity of the enzyme for CO2. The Km (RuBP) of the enzyme from various sources ranges from 10-136 .mu.M, mean .+-. SD = 36 .+-. 20 .mu.M. This variation in Km (RuBP) does not correlate with different photosynthetic pathways but shows taxonomic patterns. Among the dicotyledons, the enzyme from crassinucellate species exhibits lower Km (RuBP) (18 .+-. 4 .mu.M) than does that from tenuinucellate species (25 .+-. 7 .mu.M).