{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Estrogen receptor alpha (ER) is a nuclear receptor for estrogens such as estradiol (the main endogenous human estrogen). The two different estrogen receptor proteins produced from the ESR1 and ESR2 genes are usually called the alpha and beta receptors."}]},{"type":"paragraph","children":[{"type":"text","value":"This ER antibody recognizes a protein of 67 kDa, which is identified as estrogen receptor (ER) alpha."}]}]}