Adaptation of the protein kinase filter paper assay to a 96-well microtiter format

Determination of a large number of kinase activities using peptide substrates, P81 phosphocellulose paper arrays and phosphor imaging

To perform phosphoproteomics and signal transduction studies, a number of protein kinase activities and levels must be simultaneously analyzed in different cell samples and correlated with phosphoprotein patterns to obtain conclusions with regard to the regulation of kinase networks. We describe here a miniaturized format of the classical phosphocellulose (P81) paper binding assay with which up to 594 kinase reactions can be simultaneously analyzed. Kinase peptide substrates possessing a minimum of three consecutive basic residues were subjected to phosphorylation in 96-well plates and aliquots of the phosphorylation reactions were spotted on arrays printed on P81 papers. Phosphorylation levels were quantified using a storage phosphor system imager. The versatility of the procedure was validated by analyzing casein kinase 2, protein kinase C, and p34cdc2/cyclin B in cell extracts and testing the effect of known inhibitors and activators on kinase activities. This improved, miniaturized version of the classical P81 paper method combines simplicity, high sensitivity, high reproducibility, high reliability, and optimal Z factors and takes into account possible sources of background signals. We discuss the possibility of automation and the advantages over other methods.

Common components of patch-clamp internal recording solutions can significantly affect protein kinase A activity

Common components of whole-cell internal recording solutions were tested both in vitro and in patch-clamp experiments for their effects on the activity of cAMP-dependent protein kinase. Potassium fluoride (KF), 440 mM trimethylamine chloride and exclusion of bovine serum albumin (BSA) decreased the activity of the enzyme, while ethylene glycol-bis (beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) and the potassium salts of aspartate, gluconate, methylsulfate and monobasic phosphate increased its activity. Addition of KF to the internal solution produced a hyperpolarizing shift in the V1/2 of Ih channel activation, consistent with the KF-induced reduction of protein kinase A activity. Therefore, consideration of the composition of internal solutions is warranted when studying channel physiology by patch-clamp techniques.