Calendar Name: seminars
Scheduled for: Tuesday, May 18 2010, 11:00 - 12:30
Event text: Prof Richard C. Leegood
Robert Hill Institute & Department of Animal and Plant
Sciences
University of Sheffield
UK
Details: "PEP Carboxykinase in Plants: An Enzyme for all Seasons"
ABSTRACT
Phosphoenolpyruvate carboxykinase (PEPCK) catalyses the
reversible nucleotide triphosphate (GTP- or ATP-)
-dependent decarboxylation of oxaloacetate to PEP and
CO2. The ATP-dependent enzyme is present in flowering
plants, fungi, algae and many bacteria, the related
GTP-dependent enzyme in animal tissues. PEPCK is present
in many plant tissues and appears to be located
exclusively in the cytosol, although it may be plastidic
in diatoms. It is regulated in some, but not all, plant
tissues by reversible protein phosphorylation. Some of
its functions in plants are well understood, such as its
role in the photosynthetic CO2-concentrating mechanisms
of C4 photosynthesis (including diatoms) and in
Crassulacean Acid Metabolism. In these, PEPCK provides
CO2 for the Calvin cycle by decarboxylating OAA derived
from C4 acids. Its role in gluconeogenesis following
germination of fat-storing seeds is also well studied.
However, in recent years it has become clear that PEPCK
is present in only certain types of cells and that its
abundance is often dependent on developmental stage. It
thus functions in far more metabolic processes in plants
than was previously realised, but, as in many animal
tissues, its function has been less easy to discern.
Within leaves, although not abundant overall, it may be
present in phloem companion cells, hydathodes, trichomes
and stomata. In stomata, data from Arabidopsis
knock-outs suggest that it plays an important role in
stomatal closure. It has been identified in a range of
tissues, such as developing seeds, flowers, roots,
vascular tissue and fruit. In developing pea or grape
seeds laying down storage proteins it is implicated in
the metabolism of incoming nitrogenous compounds. This
seminar will outline the regulation of the activity of
PEPCK in plants and discuss some of its physiological
functions.
