Au. Igamberdiev et al., Decarboxylation of glycine contributes to carbon isotope fractionation in photosynthetic organisms, PHOTOSYN R, 67(3), 2001, pp. 177-184
Carbon isotope effects were investigated for the reaction catalyzed by the
glycine decarboxylase complex (GDC; EC 2.1.2.10). Mitochondria isolated fro
m leaves of pea (Pisum sativum L.) and spinach (Spinacia oleracea L.) were
incubated with glycine, and the CO2 evolved was analyzed for the carbon iso
tope ratio (delta C-13). Within the range of parameters tested (temperature
, pH, combination of cofactors NAD(+), ADP, pyridoxal 5-phosphate), carbon
isotope shifts of CO2 relative to the C-1-carboxyl carbon of glycine varied
from +14 parts per thousand to -7 parts per thousand. The maximum effect o
f cofactors was observed for NAD(+), the removal of which resulted in a str
ong C-12 enrichment of the CO2 evolved. This indicates the possibility of i
sotope effects with both positive and negative signs in the GDC reaction. T
he measurement of delta C-13 in the leaves of the GDC-deficient barley ( Ho
rdeum vulgare L.) mutant (LaPr 87/30) plants indicated that photorespirator
y carbon isotope fractionation, opposite in sign when compared to the carbo
n isotope effect during CO2 photoassimilation, takes place in vivo. Thus th
e key reaction of photorespiration catalyzed by GDC, together with the key
reaction of CO2 fixation catalyzed by ribulose-1,5-bisphosphate carboxylase
, both contribute to carbon isotope fractionation in photosynthesis.