Comparison of the kinetic properties of ribulose bisphosphate carboxylase in chloroplast extracts of spinach, sunflower and four other reductive pentose phosphate-pathway species

Abstract

Extracts from chloroplasts of spinach [Spinacia oleracea], sunflower [Helianthus annuus] and 4 other reductive pentose phosphate (C3)-pathway spp. [Beta vulgaris, Pisum sativum, Lactuca sativa and Chenopodium bonus henricus] were measured spectrophotometrically with or without a modified preactivation procedure. In all 6 spp. this modification yielded Km (CO2) values in the range of 7-15 .mu.M and maximum velocities, at 20.degree. C, of 129-431 .mu.mol of CO2 carboxylated/h per mg of chlorophyll. In general, both the carboxylation and electron-transport capacities of sunflower were somewhat greater than that of the other species, and this is discussed in relation to the superior rates of photosynthesis believed to be displayed by the parent tissue.