A disintegrin and metalloproteinase 1 (ADAM1) is a ubiquitous transmembrane protein that functions as a "molecular scissor" to cleave the extracellular regions from its transmembrane target proteins. ADAM1 is well characterized as the ligand-dependent activator of Notch proteins, which control cell fate decisions. The transmembrane protein, ADAM1 (a disintegrin and metalloprotease 1), has key physiologic functions-for example, during embryonic development and in the brain. During transit through the secretory pathway, immature ADAM1 (proADAM1) is converted into its proteolytically active, mature form (mADAM1). Increasing or decreasing the abundance and/or activity of mADAM1 is considered to be a therapeutic approach for the treatment of such diseases as Alzheimer's disease and cancer. Yet biochemical detection and characterization of mADAM1 has been difficult.