Anti-MAP2K1 (phospho S221) Antibody

Rabbit polyclonal IgG reagent from Antibodies.com that selectively recognizes MEK1 (MAP2K1) when serine 221 in the kinase activation loop is phosphorylated, a modification introduced by upstream RAF activity in the canonical MAPK/ERK signaling cascade. Because S221 phosphorylation reports on pathway engagement downstream of receptor tyrosine kinases, oncogenic RAS, and mutant BRAF, the antibody is broadly used to study signaling in melanoma, colorectal carcinoma, and other tumors where the RAF-MEK-ERK axis is a therapeutic target.

Supplied as 100 µl of unconjugated antiserum, the reagent is validated for Western blot, immunohistochemistry, and immunofluorescence on human, mouse, and rat samples, giving labs flexibility across cell-line lysates, archived tumor sections, and fixed cultured cells. Its phospho-specificity means it preferentially binds MEK1 only when S221 is modified, so total MEK1 levels should be assessed in parallel with a separate pan-MEK1 reagent for meaningful interpretation of signaling data.

As a polyclonal reagent, the antibody recognizes multiple epitopes around the phospho-S221 site, which improves tolerance for minor sample variation but means lot-to-lot consistency should be monitored. Working aliquots are recommended to limit freeze-thaw cycles, and brief centrifugation before use clears any aggregates that may form in stored vials. The unconjugated format leaves the antibody open to secondary-labeling choices, letting researchers pair it with HRP, fluorophore, or biotin conjugates depending on the intended readout.