Chemists from UCLA and the University of Florence in Italy may have solved an important mystery about a protein that plays a key role in a particular form of amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, a progressive, fatal neurodegenerative disorder that strikes without warning. Joan Selverstone Valentine, UCLA professor of chemistry and biochemistry, has studied the protein — copper-zinc superoxide dismutase — since the 1970s, long before it was implicated in ALS in 1993. Since the link was discovered, Valentine’s laboratory has made more than two dozen mutant, ALS-causing enzymes, most of which have only one wrong amino acid out of 153, to try to understand their properties and learn what makes them toxic.