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Reference.org
Fragment antigen-binding region
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<p>The fragment antigen-binding region (Fab region) is a region on an <a href="/facts/Antibody/MX8pdTdP">antibody</a> that binds to <a href="/facts/Antigen/9JlAernG">antigens</a>. It is composed of one constant and one variable domain of each of the <a href="/facts/Immunoglobulin_heavy_chain/3H7Axuu5">heavy</a> and the <a href="/facts/Immunoglobulin_light_chain/xJdoVLfK">light chain</a>. The variable domain contains the <a href="/facts/Paratope/PnHjQp4j">paratope</a> (the antigen-binding site), comprising a set of <a href="/facts/Complementarity-determining_region/7vQrl1MW">complementarity-determining regions</a>, at the <a href="/facts/N-terminus/yKYpuaBJ">amino terminal end</a> of the <a href="/facts/Monomer/Gw3CltMb">monomer</a>. Each arm of the Y thus binds an <a href="/facts/Epitope/PL0oBuGh">epitope</a> on the antigen. </p>