Enzymic Fractionation of the Stable Carbon Isotopes of Carbon Dioxide by Ribulose-1,5-bisphosphate Carboxylase 1

• Published in: Plant physiology (Bethesda) Vol. 63; no. 5; pp. 852 - 856
• Main Authors: Wong, William W., Benedict, C. Roy, Kohel, Russel J.
• Format: Journal Article
• Language: English
• Published: 01.05.1979
• ISSN: 0032-0889; 1532-2548

The enzymic fractionation of the stable carbon isotopes of CO 2 (Δco 2 ) was determined using a purified preparation of ribulose-1,5-bisphosphate (RuBP) carboxylase isolated from cotton (a C 3 plant) leaves. The bicarbonate concentration in the reaction mixture saturated the enzyme and furnished an infinite pool of 12 CO 2 and 13 CO 2 for enzyme fractionation. The RuBP was 96 to 98% pure. The phosphoglycerate synthesized in the reaction mixtures was purified free of RuBP, phosphoglycolate, and other phosphate esters by column chromatography on Dowex 1-Cl − resin. The average Δco 2 value of −27.1% was determined from five separate experiments. A discussion of the isotope fractionation associated with photosynthetic CO 2 fixation in plants shows that the enzymic fractionation of stable carbon isotopes of CO 2 by RuBP carboxylase is of major importance in determining the δ 13 C values of C 3 plants.