The Collaborative International Dictionary of English v.0.48:

Penicillamine \Pen`i*cil"lam*ine\, n. (Chem., Med.)
   A substance (C5H11NO2S) which is a degradation product of
   the penicillins. Chemically it is 3-mercapto-D-valine. It has
   chelating properties and is used in medicine as an
   antirheumatic and to chelate copper in cases of
   hepatolenticular degeneration (Wilson's disease).
   [PJC]