JBC, Vol. 250, Issue 12, 4456-4461, Jun, 1975
Partial purification and characterization of aspartate aminotransferases from seedling oat leaves
R. E. Reed and J. L. Hess
As relatively little information is available on the properties of
aspartate aminotransferase from photosynthetic tissue, isolation and
characterization of the two major electrophoretically distinct forms of
this enzyme from seedling oat leaf homogenates were undertaken. These two
forms are designated I for the more anionic form and II for the less
anionic form. Form I, 80 to 90% of the total activity, has been purified to
a specific activity of 120 mumol/min/mg of protein (1100-fold) and is
estimated to be 90 to 95% homogeneous, as judged by analytical
polyacrylamide gel electrophoresis. Form II, 10 to 20% of the total
activity, has been purified to a specific activity of approximately 6
mumol/min/mg of protein (300-fold). Both forms exhibit optimal activity at
pH 7.5. Michaelis constants do not differ greatly between forms I and II
and are similar to those reported for the pig heart cytosolic enzyme as
well as aspartate aminotransferase from other plant sources. A molecular
weight of 130,000 for the purified aspartate aminotransferase I was
estimated by sedimentation equilibrium centrifugation; molecular weights of
the two forms are similar as estimated by sucrose density gradient
centrifugation. No activation by pyridoxal phosphate has been observed
during purification.
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