Enhancement of luminol chemiluminescence by cysteine and glutathione

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 sig nals in the presence and absence of cysteine; standard errors were generall y <5% of the mean ratio. Cystine in sufficiently acidic solution also enhan ces the chemiluminescence but otherwise diminishes the emission. The emissi on is also inhibited by glutathione. A mixed solution of cysteine and cysti ne gives rise to enhanced signals. In all the above cases, enhancement occu rs only in the presence of a cobalt(II) catalyst. Luminol-peroxynitrite che miluminescence is enhanced by cysteine and by glutathione without the prese nce of a catalyst.