Fractionation of carbon (¹³C/¹²C) isotopes in glycine decarboxylase reaction

Abstract

Fractionation of carbon isotopes (13C/12C) by glycine decarboxylase (GDC) was investigated in mitochondrial preparations isolated from photosynthetic tissues of different plants (Pisum, Medicago, Triticum, Hordeum, Spinacia, Brassica, Wolffia). 20 mM glycine was supplied to mitochondria, and the CO2 formed was absorbed and analyzed for isotopic content.CO2 evolved by mitochondria of Pisum was enriched up to 8 %o in 12C compared to the carboxylic atom of glycine. CO2 evolved by mitochondria of the other plants investigated was enriched by 5-16 %o in 13C. Carbon isotope effects were sensitive to reaction conditions (pH and the presence of GDC cofactors). Theoretical treatment of the reaction mechanism enabled us to conclude that the value and even the sign of the carbon isotope effect in glycine decarboxylation depend on the contribution of the enzymesubstrate binding step and of the decarboxylation step itself to the overall reaction rate. Therefore, the fractionation of carbon isotopes in GDC reaction was revealed which provides essential isotopic effects in plants in addition to the well-known effect of carbon isotope fractionation by the central photosynthetic enzyme, ribulose-l,5-biphosphate carboxylase.

Oscillations of the internal CO2 concentration in tobacco leaves transferred to low CO2

“…He proposed also that carbon isotope fractionation during photosynthesis is connected at least in part to depletion of CO 2 by Rubisco and its release during glycine decarboxylation (Ivlev, 1989). Subsequent studies have experimentally verified this hypothesis (Ivlev et al, 1996;Igamberdiev et al, 2001Igamberdiev et al, , 2004.…”

Carbon Isotope Fractionation during Photorespiration and Carboxylation in Senecio

“…Theory predicts interactions between f and e, but these are minor across the range of plausible f values (Tcherkez, 2006). The in vitro estimates of g for different C 3 species (Table II) span a large range of 216& to 18& (Ivlev et al, 1996;Igamberdiev et al, 2001;Ivlev, 2001). However, these results cannot easily be related to f. The measurements were performed on purified enzymes or isolated mitochondria at a range of pH values and with various cofactors (e.g.…”

Annual cyclicity in high‐resolution stable carbon and oxygen isotope ratios in the wood of the mangrove tree Rhizophora mucronata

“…Dark respiration and photorespiration were shown to cause 13 C enrichment of respired CO 2 relative to the plant material (cf. Ivlev, Bykova & Igamberdiev 1996;Duranceau et al 1999;Ghashghaie et al 2001), which, depending on the respiration rate, may significantly deplete the plant material. Duranceau et al (1999) found a depletion of 1‰ in the plant material, which was attributed to dark respiration.…”