Kinetics of induction of MAP kinase activity by NGF in HMC-1 mast cells. HMC-1 cells were stimulated with NGF (100 ng/mL) for 5, 15, 30, or 60 minutes. pp44ERK-1 MAP kinase was partially purified from HMC-1 cells using an immunoaffinity column. MAP kinase activity of the eluted antigen was quantified by a substrate peptide kinase assay using myelin basic protein as the substrate, and the specific activity was expressed as cpm/μg eluted protein. The results shown are the mean ± standard error of mean (SEM) of values obtained from four separate experiments.