An N-acetyl modified version of this compound is administered to treat acetaminophen overdose.
An N-acetyl modified version of this compound is administered to treat acetaminophen overdose. A "string protein" named for this compound interacts with several SNAREs and is heavily palmitoylated on this residue near the C-terminus. It's not lysine, but ubiquitin is first attached to this amino acid in the E1 ubiquitin activating enzyme, and then transferred to this amino acid again on the E2 ubiquitin conjugating enzyme. Papain is an example of this amino acid's namesake class of proteases. Beta-(*)mercaptoethanol is used to cleave bonds formed by this amino acid. This amino acid is oxidized in the endoplasmic reticulum by the protein PDI. This amino acid's side chain is a thiol group, which allows it to form disulfide bonds. For 10 points, name this amino acid that is the only standard one other than methionine to have a sulfur. 
An N-acetyl modified version of this compound is administered to treat acetaminophen overdose.
cysteine [or Cys; prompt on "C"] 