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

1978 ◽  
Vol 171 (2) ◽  
pp. 477-482 ◽  
Author(s):  
M E Delaney ◽  
D A Walker
Keyword(s):  
Electron Transport ◽  
Pentose Phosphate Pathway ◽  
Pentose Phosphate ◽  
The Other ◽  
Kinetic Properties ◽  
Ribulose Bisphosphate Carboxylase ◽  
Ribulose Bisphosphate ◽  
Bisphosphate Carboxylase

Extracts from chloroplasts of spinach, sunflower and four other reductive pentose phosphate (C3)-pathway species were measured spectrophotometrically with or without a modified preactivation procedure. In all six species this modification yielded Km (CO2) values in the range of 7-15 micron and maximum velocities, at 20 degrees C, of 129-431 mumol 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.

Ribulose bisphosphate carboxylase—oxygenase: its role in photosynthesis

1986 ◽  
Vol 313 (1162) ◽  
pp. 305-324 ◽  
Keyword(s):  
Electron Transport ◽  
Carbon Assimilation ◽  
Kinetic Properties ◽  
Ribulose Bisphosphate Carboxylase ◽  
Ribulose Bisphosphate ◽  
Rubp Carboxylase ◽  
Bisphosphate Carboxylase ◽  
Triose Phosphate ◽  
Ribulose Bisphosphate Carboxylase Oxygenase

Synthesis of triose phosphate by the chloroplast requires three substrates: light, CO 2 and orthophosphate (P i ). In the response of the rate of carbon assimilation to the concentration of CO 2 , the kinetic properties of RuBP carboxylase-oxygenase (Rubisco) constitute the main limitation at low CO 2 concentrations, while at higher concentrations of CO 2 the limitation is shifted towards the reactions leading to the regeneration of the substrate, RuBP, driven by electron transport. In these circumstances, light or P i or both, can become limiting. The characteristics of Rubisco that can affect photosynthesis fall under three main headings: (1) amount and kinetic constants; (2) activation state; and (3) regulation of catalysis (including the role of effectors, such as Pt and glycerate 3-phosphate (PGA)). These characteristics are analysed, and the role of changes in activity of the enzyme is discussed in the context of limitation and regulation of the photosynthetic process. Other factors considered are the regeneration of RuBP and its relation to electron transport, P i supply, and photorespiration. The influence that expected increases in atmospheric CO 2 concentration, and/or genetic improvements in the characteristics of the enzyme, may have on the present balance between the partial processes of photosynthesis, is discussed.

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