Detection of tyrosine phosphatase activity in Catharanthus roseus hairy roots

We determined the presence of protein tyrosine phosphatase (EC 3.1.3.48) activity (PTP) in Catharanthus roseus transformed roots. Increased concentrations of sodium orthovanadate, a PTP inhibitor, induce higher levels of tyrosine phosphorylation in two proteins (43 and 63 kDa) present in the soluble fraction. PTP was also tested using an exogenous substrate RR-SRC-PY, a synthetic peptide with a single phosphotyrosine residue, derived from the amino acid sequence surrounding the phosphorylation site in pp60src. PTP activity was observed in the soluble and in the particulate fractions. This activity was inhibited by sodium orthovanadate and stimulated by β-mercaptoethanol. These results indicate, for the first time, the presence of PTP activity in transformed plant tissues.