I work as a structural biochemist and I contest the statement that cysteine is an uncountable noun. This is true for those thinking on the macroscale about the amino acid as a chemical substance, but is untrue for those working with specific proteins. Specific proteins contain a countable number of each amino acid, one of which is cysteine. It is very common to hear a statement like "protein disulfide isomerase contains two cysteines." Just google the phrase "contains two cysteines" in quotes. You'll get many examples.
- That may be so, but it is still dodgy English - the correct terminology is "cysteine residues". --Williamsayers79 19:31, 9 October 2008 (UTC)