Not much progress on the purification and characterization of low molecular weight acid phosphatases from plants has been made as yet. In the current study a low molecular weight acid phosphatase from seedling of melon was purified about 114-fold with specific activity of 45 U/ mg of protein and a recovery of 3 %. The enzyme was found to be homogeneous and showed a single band corresponding to 29 kDa on SDS-polyacrylamide gel electrophoresis. The Km for p-nitrophenyl phosphate was found to be 0.175 mM and Vmax was 42 µmol of substrate hydrolyzed /min/mg of protein at pH 5.5 and at 37° C. The enzyme showed its optimum activity at pH 5.0 and 50o C. The enzyme was thermostable and it retained 70 % activity for 45 min at 60o C. The pH stability was 4.8-6.0. Phosphate, vanadate, molybdate and fluoride acted as strong inhibitors. Metal ions such as Zn+2, Cu+2, Ag+1 and Hg+2 deactivated the enzyme while other divalent ions such as Ca+2 and Mg+2 had no effect.

Umber Zaman, Rubina Naz, Asma Saeed, Mehrin Sherazi and Ahmad Saeed