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Reference.org
Accessible surface area
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<p>The accessible surface area (ASA) or solvent-accessible surface area (SASA) is the <a href="/facts/Surface_area/WNowzFCw">surface area</a> of a <a href="/facts/Biomolecule/DGvFzN7R">biomolecule</a> that is accessible to a <a href="/facts/Solvent/LoMPMz8S">solvent</a>. Measurement of ASA is usually described in units of square <a href="/facts/Angstrom/T5mjdd97">angstroms</a> (a standard unit of measurement in <a href="/facts/Molecular_biology/YgqU35ub">molecular biology</a>). ASA was first described by Lee & Richards in 1971 and is sometimes called the Lee-Richards molecular surface. ASA is typically calculated using the 'rolling ball' algorithm developed by Shrake & Rupley in 1973. This algorithm uses a sphere (of solvent) of a particular <a href="/facts/Radius/9Gr9deYD">radius</a> to 'probe' the surface of the <a href="/facts/Molecule/N9ljSfFq">molecule</a>. </p>