Enzymatic fractionation of carbon isotopes by phosphoenolpyruvate carboxylase from c(4) plants |
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| Authors: | Whelan T Sackett W M |
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| Affiliation: | Department of Oceanography, Texas A & M University, College Station, Texas 77843. |
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| Abstract: | The carbon atoms of glucose and malate in C4 plants are 2 to 3‰ enriched in 12C with respect to atmospheric CO2; whereas these intermediates in C3 plants are 15 to 18‰ enriched with 12C with respect to atmospheric CO2. The enzymatic synthesis of malate from phosphoenolpyruvate and bicarbonate in preparations of leaves of Sorghum bicolor, Haygrazer result in a carbon isotope fractionation of about 3‰. The enzymatic synthesis of phosphoglyceric acid from ribulose 1,5-diP and CO2 in these preparations (contaminated with carbonic anhydrase) at 24 C and 37 C result in a carbon isotope fractionation of 33.7‰ and 18.3‰, respectively. These data are consistent with the conclusion that the small enrichment of 12C in the carbon atoms of malate and glucose (with respect to atmospheric CO2) in leaves of Sorghum bicolor, Haygrazer occurs at the phosphoenolpyruvate carboxylase step. |
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