Isolation and some properties of acid phosphatase-1(1) from tomato leaves

An isozyme of acid phosphatase-1, acid phosphatase-1(1), was purified from the leaves of tomato (Lycopersicon esculentum) to homogeneity and characterized. The purified enzyme was homogeneous on polyacrylamide gel electrophoresis with or without sodium dodecyl sulfate. The gel filtration analysis showed that the native molecule had a relative molecular mass of about 61 kilodaltons (kDa). The relative molecular mass of the subunit on gel electrophoresis with sodium dodecyl sulfate was about 32 kDa, indicating that the native form of the enzyme was a homodimer. It was suggested by periodic acid-Schiff staining on the gel that the enzyme was a glycoprotein. The Km for p-nitrophenylphosphate was 2.9 x 10(-3) M. The enzyme had a pH optimum of 4.5 in 0.15 M potassium acetate buffer with p-nitrophenylphosphate as a substrate. This enzyme was activated by divalent metal ions, such as Zn2+, Mg2+, and Mn2+. The N-terminal amino acids were sequenced after the purified enzyme was treated with pyroglutamylpeptidase. It was suggested that the N-terminal amino acid was pyroglutamate.