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.