Side chain polarity Reset Display the thio alcohol (thiol) group as Ball & Stick. Cys differs structurally from Ser only in the sulfur for oxygen substitution. Cys is found in the apolar interior of proteins more often than Ser; it also forms covalent disulfide bonds with other Cys residues to help stabilize the tertiary folding of extracellular proteins. Some facts on L-cysteine. Abbreviation: Cys. One-letter code: C. Molecular mass: 121 daltons. Side chain (or R-group) features: Structural formula: Formula: -CH2-SH; Category: nonpolar; neutral. pKa: 8.3. Return to image of Cys.
Some facts on L-cysteine.