Variations in the Specific Activity of Ribulose-1,5-bisphosphate Carboxylase between Species Utilizing Differing Photosynthetic Pathways

Abstract

Carnegie Institution of Washington, Stanford, California 94305 (J. A. B.) MATERIALS AND METHODSThe in vitro specific activity of ribulose-1,5-bisphosphate carboxylase (RuBPCase) (micromoles CO2 fixed per minute per milligram enzyme) from a number of C3 and C4 species and one green alga were measured. RuBPCases from species which utilize the C4 pathway have a specific activity -2-fold higher than those from C3 species. RuBPCase from Chlamydomonas reinhardtii has a specific activity similar to the C4 enzyme. Higher specific activity forms of RuBPCase are associated with a decreased enzyme affiity for CO2 (increased K4C021). A small but significant difference in the specific activity of RuBPCase from two C4 decarboxylation types was also observed. The relationship between enzymic properties and the presence or absence of a CO2 concentrating mechanism is discussed.RuBPCase3 (EC 4.1.1.39) catalyzes the primary CO2 fixation reaction in all photosynthetic organisms. However, the concentration of CO2 (and 02) at the site of carboxylation can differ markedly between such organisms as a consequence of the presence or absence of CO2 concentrating mechanisms. It has been suggested that differences in the kinetic properties of RuBPCase may be an evolutionary result of such variation in the CO2 concentration available to the enzyme (14,22). Previous studies have generally concentrated upon the Km(CO2) of the enzyme (5, 21, 22). There is, however, little data available concerning variation in specific activity (turnover number) of RuBPCase between species which utilize a CO2 concentrating mechanism, particularly the C4 pathway. To determine if a consistent relationship exists between the affinity for CO2 of the enzyme and its catalytic turnover number, we have measured the specific activity of RuBPCase from a variety of C4 species representing the three decarboxylation type (NADP-ME, NAD-ME, PCK), from a number of C3 species and from Chiamydomonas reinhardtii, a green alga. 'CIW Publication No. 843.

Varying Photoperiod, Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase and CO2 Uptake in Thalassiosira fluviatilis (Bacillariophyceae)

“…The conversion was carried out assuming that carbon is 47% of the mol wt of the enzyme protein, computed from the amino acid composition of maize RuBP C/O-ase (14). The best value of P was taken to be the mean ofthe three estimates ( Table Table III These results are compatible with enzyme kinetics from organisms having carbon concentrating mechanisms (16). T. fluviatilis has optimum growth conditions characterized by a large variation in salt concentrations (15- 30 g kg-'), a temperature of about 25C, and a pH between 7.8 and 8.4 (L. A. Hobson, unpublished data).…”

“…Concentrations of enzyme were measured instead of activity because results with T. fluviatilis suggested that measurements of RuBP C/O-ase ' Supported in part by operating (A6476) and strategic (G0864) grants from the Natural Sciences and Engineering Research Council of Canada. activity by techniques applicable to algae (16) were unreliable and insensitive to activation methods (15). We England Nuclear) was added to each of one set of three cultures prior to cell inoculation.…”

Exchange Properties of the Activator CO2 of Spinach Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase

“…If it is assumed that the binding of one CO2 is associated with activation of a single RuBisCO site, then the data in this figure indicate that the turnover number ofthe enzyme is 2.8 s-'. While this turnover number is somewhat lower than that observed for the purified enzyme in Figure 1 (5 s-'), turnover numbers of approximately 3 to 5 s-' have been previously reported (2,17 Time, min FIG. 3.…”

The Catalytic Properties of Hybrid Rubisco Comprising Tobacco Small and Sunflower Large Subunits Mirror the Kinetically Equivalent Source Rubiscos and Can Support Tobacco Growth

“…Only needing to engineer rbcL would be advantageous as it would negate the need for cotransplanting in the complementary RbcS and evade further obstacles with needing to silence the endogenous S or genetically manipulate it as this is complicated by the multiple RbcS copies in the nuclear genome . Candidate rbcL genes for testing would include those of the kinetically superior Rubiscos from C 3 plants growing in hot arid conditions (Galmes et al, 2005), such as Limonium gibertii (Parry et al, 2007) whose L shows 92% identity to tobacco L. A wider examination might also include rbcL genes from C 4 Rubiscos that characteristically have higher k c cat values relative to C 3 species, albeit at the expense of higher K c values (Yeoh et al, 1981;Seemann et al, 1984).…”