Signal transduction is the process by which a cell recognizes changes in its environment and transforms that signal into modifications in cellular activity and gene expression. These processes are often initiated through receptor ligation or stress, and may involve a cascading series of intracellular biochemical events that are amplified and integrated to achieve the desired cellular response. For instance, activated kinases can catalyze the transfer of a phosphate group to serine, threonine, or tyrosine residues on target proteins and regulate protein activity, localization, and protein-protein interactions. Activities modified by phosphorylation can in turn be terminated by the phosphatases. Signal transduction cascades may also involve non-enzymatic second messengers including cyclic nucleotides (cAMP and cGMP), Ca2+, and lipids. These intracellular signaling events regulate virtually all cellular activities. Therefore, it is critical to have quality tools that make it easy to study factors involved in signal transduction.