Fig. 1

Thiophosphorylation and auto-thiophosphorylation catalyzed by Src kinase. a. The activity of Src kinase domain (450 nM) toward a synthetic peptide substrate (AEEEIYGEFEAKKKKG, 800 μM) was measured using the continuous spectrophotometric assay. The reactions contained no ion/nucleotide (squares), 10 mM MgCl₂ and 2 mM ATPγS (circles), or 10 mM NiCl₂ and 2 mM ATPγS (triangles). Absorbance data were recorded every 8 s. b. The activity of Src (2.2 μM) was measured in the absence of peptide substrate using the continuous spectrophotometric assay. The reactions contained 10 mM divalent cation (Mg²⁺ or Ni²⁺) and 2 mM nucleotide (ATP or ATPγS), as indicated