It took a high-tech combination of Fourier transform Raman spectroscopy, computer simulations, and enzyme kinetics, but researchers have proven a long-standing presumption about why people's hair turns gray (FASEB J., DOI: 10.1096/fj.08-125435). The root of the problem, according to Karin U. Schallreuter of the University of Bradford, in England, and colleagues, is an excess of endogenous hydrogen peroxide. The researchers detected high levels of H2O2 in gray and white hair but found none in brown hair. They say that H2O2 builds up because of a decline in the production of catalase, an enzyme that decomposes peroxide. The H2O2 in turn oxidizes methionine residues in hair proteins, such as tyrosinase, a process that limits tyrosinase's capacity to produce hair pigment. Two other enzymes, methionine sulfoxide reductase A and B, normally reverse methionine oxidation. But the researchers found that the high levels of H2O2 present in graying hair damage these enzymes and overwhelm their repair capabilities. Schallreuter's team showed that free L-methionine can prevent oxidation of methionine residues in proteins in vitro. The next step is to see if this strategy will work in vivo.