C-Kit is the receptor tyrosine kinase for stem cell factor (SCF) and is a member of the subfamily that includes PDGF, CSF-1 and FLT-3/flk-2 receptors (1,2). It plays critical controlling roles in a number of cell types such as hematopoietic stem cells, mast cells, melanocytes and germ cells (3). Upon binding with its ligand, c-Kit receptors are induced undergoing dimerization/ oligomerization and autophosphorylation. Activation of c-Kit results in the recruitment and tyrosine phosphorylation of downstream SH2-containing signaling components including PLCgamma, p85 subunit of PI3 kinase, SHP2 and CrkL (4), which links c-Kit directly to various cell signaling pathways. Molecular lesions that impair the kinase activity of c-Kit are associated with a variety of developmental disorders (5), while mutations that constitutively activate c-Kit can lead to pathogenesis of mastocytosis and gastrointestinal stromal tumors (6). Tyrosine 719 is located in the kinase insert region of the catalytic domain. c-Kit phosphorylated at Tyr719 binds to the p85 subunit of PI3 kinase in vitro and in vivo (7).Human Kit (GenBank Accession No. BC071593), (a.a. 544-end) with N-terminal His tag, MW 53.4kD, expressed in an Baculovirus infected Sf9 cell expression system.Specific Activity: 15 U/mg. One unit is defined as the amount of enzyme that will incorporate 1nmol phosphate to the tyrosine substrate per minute at pH 7.4 and 30°C. Assay buffer: 50mM HEPES, pH 7.4, 3mM MgCl2, 3mM MnCl2, 1mM DTT, 3uM Na-orthovanadate, 0.1mM ATP, 30ug/ml Poly (Glu:Tyr)4:1 substrate, and 4ug /ml recombinant c-Kit.Application: useful for the study of enzyme kinetics, screening inhibitors, and selectivity profiling.Stability: >6 months at –80°C