Journal of Experimental Botany, Vol 49, 807-816, Copyright © 1998 by Oxford University Press
M Esquivel, R Ferreira and A Teixeira
Determining the degradation characteristics of proteins is difficult due to
the lack of appropriate methodologies, particularly in the case of leaf
proteins. Previous studies suggest that ribulose bisphosphate carboxylase
(RuBP carboxylase; EC 4.1.1.39) proteolysis may be fundamentally different
in C3 and C4 plants. To test this hypothesis, the relative degradation
rates of the total soluble protein, RuBP carboxylase and glycolate oxidase
(EC 1.1.3.1) in the second leaves of intact C3 (Triticum
aestivum L.) and C4 (Zea mays L) and
Sorghum bicolor L.)plants was measured. The
methodology utilized involved an efficient procedure to label the leaf
proteins, the use of a double-labelling method to measure protein
degradation and a single-step purification of the labelled proteins under
study. RuBP carboxylase is subjected to continuous degradation in all
plants investigated. Its rate of degradation is higher for Z.
mays, intermediate for T. aestivum and
lower for S. bicolor. When the rate of RuBP
carboxylase degradation was compared with that of the total soluble protein
a differential pattern was obtained for the plant species examined: whereas
maize presents a faster rate of RuBP carboxylase degradation than of the
total soluble protein, wheat and sorghum show similar rates. However, the
rate of RuBP carboxylase proteolysis in the three plant species studied is
much lower than the rate of glycolate oxidase degradation. The results
obtained indicate that, under the conditions of study, the degradation
characteristics of plant RuBP carboxylase, as those of glycolate oxidase,
are species specific, in a way suggesting that they do not depend on the
type of photosynthetic metabolism of the species considered (C3 or
C4).Keywords: C3 plants, C4 plants, glycolate oxidase,
protein degradation, ribulose bisphosphate carboxylase.
ARTICLES
Protein degradation in C3 and C4 plants with particular reference to ribulose bisphosphate carboxylase and glycolate oxidase
Departamento de Botanica e Engenharia Biologica, Instituto Superior de Agronomia, Universidade Tecnica de Lisboa, 1399 Lisboa Codex, Portugal; Instituto de Tecnologia Quimica e Biologica, Universidade Nova de Lisboa, Apartado 127, 2780 Oeiras, Portugal; Corresponding author; e-mail: rbferreira@isa.utl.pt
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