Effect of 14-3-3 on PI 3-kinase enzyme activity.

A peptide (Y751) corresponding to the p85 binding site on the PDGF receptor was coupled to Actigel Superflow resin. Six hundred microliters of platelet cytosol (12 mg/mL) was incubated with 60 μL of a 50% slurry of the peptide-coupled resin. The resin was pelleted and incubated with the indicated concentrations of recombinant GST (gray bars) or 14-3-3ζ–GST (black bars), and PI 3-kinase assays were performed on washed pellets using PtdIns as the substrate. Enzyme activity is expressed as a percentage of that observed in control reactions performed in the absence of recombinant GST or 14-3-3ζ–GST. Results represent the mean ± SD of 3 experiments.