PLANT PHYSIOLOGY , Vol 114, Issue 3 907-915, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Biochemical Characterization and Subcellular Localization of the Red Kidney Bean Purple Acid Phosphatase
A. G. Cashikar, R. Kumaresan and N. M. Rao
Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
Phosphatases are known to play a crucial role in phosphate turnover in
plants. However, the exact role of acid phosphatases in plants has been
elusive because of insufficient knowledge of their in vivo substrate and
subcellular localization. We investigated the biochemical properties of a
purple acid phosphatase isolated from red kidney bean (Phaseolus vulgaris)
(KBPAP) with respect to its substrate and inhibitor profiles. The kinetic
parameters were estimated for five substrates. We used 31P nuclear magnetic
resonance to investigate the in vivo substrate of KBPAP. Chemical and
enzymological estimation of polyphosphates and ATP, respectively, indicated
the absence of polyphosphates and the presence of ATP in trace amounts in
the seed extracts. Immunolocalization using antibodies raised against KBPAP
was unsuccessful because of the non-specificity of the antiserum toward
glycoproteins. Using histoenzymological methods with ATP as a substrate, we
could localize KBPAP exclusively in the cell walls of the peripheral two to
three rows of cells in the cotyledons. KBPAP activity was not detected in
the embryo. In vitro experiments indicated that pectin, a major component
of the cell wall, significantly altered the kinetic properties of KBPAP.
The substrate profile and localization suggest that KBPAP may have a role
in mobilizing organic phosphates in the soil during germination.
