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Contributed by Philip W Miller, Waltraud I Dunn, and Robert R Schmidt,
University of Florida, Dept. Microbiology and Cell Science, Gainesville,
FL 32611 USA
Florida Agricultural Experiment Station Serial Number T-00256
Introduction
One of the research goals of this laboratory is to elucidate the pre-
and posttranslational mechanisms that regulate both carbon and nitrogen
metabolism in plants. Chlorella sorokiniana, a unicellular green
alga, has been used extensively as a model system to study enzymes involved
in higher plant metabolism. Research in this laboratory has shown that
Chlorella sorokiniana possesses seven ammonium inducible, chloroplastic,
NADP-specific glutamate dehydrogenase (NADP-GDH) isoenzymes that are regulated
by both nitrogen and carbon metabolites (Prunkard et al. 1986). Biochemical,
immunochemical, and physical characterization of purified GDH homohexamers
revealed that the subunits (α, 55.5 kD; , 53 kD) composing these
holoenzymes are nearly identical; however, kinetic characterization of
the enzymes showed them to have strikingly different Km values,
allosteric properties, and turnover rates (Bascomb and Schmidt 1987).
Recent molecular genetic analysis indicates that minor modifications in
the primary protein sequences may account for these observed properties.
In order to further elucidate the regulation of these isoenzymes, it was
necessary to purify to homogeneity a large quantity of active enzyme for
polyclonal/monoclonal antibody production and additional protein analysis.
We report here the use of the Model 491 prep cell for the purification
of native NADP-GDH protein by nondenaturing PAGE with <2% loss
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