Fig. 4. Inhibition of Src kinase activity in vitro. (A) Coomassie staining of SDS-PAGE of purified GST-fusion proteins. (B,D) In vitro protein kinase assay were performed with 5 units of purified Src together with 5 µM GST, 0.5-2.0 µM GST-APRO4 or 5 µM of GST-APRO4C and enolase. Enolase was used as an exogenous substrate for measuring Src activity. ³²P-labelled proteins were resolved by SDS-PAGE and visualized by autoradiography. Data are representative of four independent experiments. (C,E) Quantification of data obtained in (B) and (D). The incorporation of ³²P into enolase was quantified by scanning densitometry. Data represent average values from four independent experiments and are expressed relative to those for purified Src with the addition of GST alone. Error bars indicate standard errors.