Enhancement of luminol chemiluminescence by cysteine and glutathione

Abstract

Cysteine enhancement of cobalt(II)-catalysed chemiluminescence of hydrogen peroxide and luminol occurs in carbonate buffer (but not in borate buffer), whether cysteine mixes with hydrogen peroxide before it mixes with luminol–cobalt(II) or vice versa. Enhancement was measured by the ratio of the signals in the presence and absence of cysteine; standard errors were generally <5% of the mean ratio. Cystine in sufficiently acidic solution also enhances the chemiluminescence but otherwise diminishes the emission. The emission is also inhibited by glutathione. A mixed solution of cysteine and cystine gives rise to enhanced signals. In all the above cases, enhancement occurs only in the presence of a cobalt(II) catalyst. Luminol–peroxynitrite chemiluminescence is enhanced by cysteine and by glutathione without the presence of a catalyst.