1. Abbreviation for sacral vertebra (S1–S5); spheric, spheric lens; Svedberg unit.
2. Symbol for siemens; sulfur; entropy in thermodynamics; substrate in the Michaelis-Menton mechanism; percentage saturation of hemoglobin (when followed by subscript O2 or CO); serine; seryl; one of the two stereochemical designations (in italics) in the Cahn-Ingold-Prelog system.
3. Designation of a rare human antigen (hemagglutinogen) related genetically to the MNSs blood group. See Blood Groups Appendix.
4. Fourth product in a multisubstrate enzyme.
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