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|Title:||Variation in the Substrate Specificity of Ribulose-1,5-Bisphosphate Carboxylase/oxygenase|
|Author(s):||Jordan, Douglas Brian|
|Department / Program:||Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The kinetic properties of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase were investigated in order to identify conditions which alter the carboxylation and oxygenation functions differentially. Primary emphasis was on the CO(,2)/O(,2) specificity factor (SF = V(,c)K(,o)/V(,o)K(,c)) which was determined by measuring the rates of carboxylation and oxygenation of RuBp at known concentrations of CO(,2) and O(,2). A sensitive assay procedure was developed for the simultaneous measurement of RuBP carboxylase and oxygenase activities. The activation state of the enzyme, the pH, the concentration of RuBP, and several chemicals did not affect the value of the SF. The SF was affected by the bivalent metal cofactor, the species origin of the enzyme, and the temperature.
Replacement of Mg('2+) by Mn('2+) was found to decrease the SF by a factor of about 20 for the RuBP carboxylase/oxygenases from several species. The major differential effect of the two metals was on the K(,m)(O(,2)). Considerable variation was found in the SF of the RuBP carboxylase/oxygenases purified from different species. The SF values ranged from about 12 in the single subunit type enzymes from photosynthetic bacteria to about 48 in the cyanobacteria to 54 in Euglena gracilis to 62 in green algae to 80 in higher plants with C(,3) photosynthesis. The major cause of variation in the SF was changed in the K(,m)(CO(,2)). With the exception of some C(,4) plants, species which have CO(,2) concentrating mechanisms had RuBP carboxylase/oxygenases with smaller SF values in comparison to the enzymes from species without this ability. The SF of spinach RuBP carboxylase/oxygenase decreased with increasing temperatures having a Q(,10) value of 0.76 between 5 and 40 C. Over this temperature range, the SF quantitatively predicted the CO(,2) compensation concentrations for several C(,3) plants, supporting the hypothesis that the SF determines the relative amount of photosynthesis and photorespiration in these species. The temperature dependence of K(,m)(CO(,2)) was much larger than that of K(,m)(O(,2)).
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.
|Date Available in IDEALS:||2015-05-14|