BIOCHEMICAL-CHARACTERIZATION AND SUBCELLULAR-LOCALIZATION OF THE RED KIDNEY BEAN PURPLE ACID-PHOSPHATASE

Phosphatases are known to play a crucial role in phosphate turnover in plants. However, the exact role of acid phosphatases in plants has be en elusive because of insufficient knowledge of their in vivo substrat e and subcellular localization. We investigated the biochemical proper ties of a purple acid phosphatase isolated from red kidney bean (Phase olus vulgaris) (KBPAP) with respect to its substrate and inhibitor pro files. The kinetic parameters were estimated for five substrates. We u sed P-31 nuclear magnetic resonance to investigate the in vivo substra te of KBPAP. Chemical and enzymological estimation of polyphosphates a nd ATP, respectively, indicated the absence of polyphosphates and the presence of ATP in trace amounts in the seed extracts. Immunolocalizat ion using antibodies raised against KBPAP was unsuccessful because of the nonspecificity of the antiserum toward glycoproteins. Using histoe nzymological methods with ATP as a substrate, we could localize KBPAP exclusively in the cell walls of the peripheral two to three rows of c ells 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.