The invention discloses novel phosphorylation sites identified in signal transduction proteins and pathways, and provides phosphorylation-site specific antibodies and heavy-isotope labeled peptides (AQUA peptides) for the selective detection and quantification of these phosphorylated sites/proteins, as well as methods of using the reagents for such purpose. Among the phosphorylation sites identified are sites occurring in the following protein types: adaptor/scaffold proteins, adhesion/extracellular matrix protein, apoptosis proteins, calcium binding proteins, cell cycle regulation proteins, chaperone proteins, chromatin, DNA binding/repair/replication proteins, cytoskeletal proteins, endoplasmic reticulum or golgi proteins, enzyme proteins, G/regulator proteins, inhibitor proteins, motor/contractile proteins, phosphatase, protease, Ser/Thr protein kinases, Protein kinase (Tyr)s, receptor/channel/cell surface proteins, RNA binding proteins, transcriptional regulators, tumor suppressor proteins, ubiquitan conjugating system proteins and proteins of unknown function.