Characterization of High and Low Molecular Mass Isoforms of Phosphoenolpyruvate Carboxylase from the Green Alga Selenastrum Minutum
Phosphoenolpyruvate carboxylase (PEPC) is a ubiquitous cytosolic enzyme in plants and is also found in a wide range of prokaryotes (1). This enzyme has been extensively studied and characterized in higher plants, in particular in C4 and CAM leaves. In contrast, lower plant PEPCs have only received a modest amount of attention. However, physiological studies in C3 green algae have shown that, in these organisms, PEPC is a key enzyme involved in anaplerotic C fixation during N assimilation (2,3). This is an important enzyme to study because approximately 70% of global N assimilation occurs in algal cells. We have recently purified PEPC from two green algae Selenastrum minutum (4) and Chlamydomonas reinhardtii (5) and found multiple PEPC isoforms in these unicellular organisms. In this paper, we present an overview of our current knowledge on the kinetic and structural properties and of green algal PEPCs and propose a model for the structural organization of PEPC in green algae.
Key wordsPEPC green algae protein-protein interaction C metabolism N metabolism phosphorylation/dephosporylation
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