PLANT PHYSIOLOGY , Vol 113, Issue 1 235-241, Copyright © 1997 by American Society of Plant Biologists
|
BIOCHEMISTRY AND ENZYMOLOGY |
Multiple Forms of ADP-Glucose Pyrophosphorylase from Tomato Fruit
B. Y. Chen and H. W. Janes
Department of Plant Science, Rutgers University, New Brunswick, New Jersey 08903
ADP-glucose pyrophosphorylase (AGP) was purified from tomato (Lycopersicon
esculentum Mill.) fruit to apparent homogeneity. By sodium dodecyl
sulfate-polyacrylamide gel electrophoresis the enzyme migrated as two close
bands with molecular weights of 50,000 and 51,000. Two-dimensional
polyacrylamide gel electrophoresis analysis of the purified enzyme,
however, revealed at least five major protein spots that could be
distinguished by their slight differences in net charge and molecular
weight. Whereas all of the spots were recognized by the antiserum raised
against tomato fruit AGP holoenzyme, only three of them reacted strongly
with the antiserum raised against the potato tuber AGP large subunit, and
the other two spots (with lower molecular weights) reacted specifically
with antisera raised against spinach leaf AGP holoenzyme and the potato
tuber AGP small subunit. The results suggest the existence of at least
three isoforms of the AGP large subunit and two isoforms of the small
subunit in tomato fruit in vivo. The native molecular mass of the enzyme
determined by gel filtration was 220 [plus or minus] 10 kD, indicating a
tetrameric structure for AGP from tomato fruit. The purified enzyme is very
sensitive to 3-phosphoglycerate/inorganic phosphate regulation.