Peroxidase-catalysed chlorophyll destruction accompanied by the formation of electronically excited states: Chlorophyll emission not due to energy transfer from excited substrate metabolites

The peroxidase-catalysed oxidative degradation of chorophyll-a (chi-a) in the absence or presence of 2,4-dichlorophenol (DCP) is accompanied by the generation of electronically excited states, as indicated by light emission in the red spectral region. A mechanism for the destruction of chi-a is proposed, which takes into account the formation of excited states. As peroxidative chi destruction is believed to be a naturally occurring degradation process, the formation of potentially deleterious excited states during degradation is of physiological importance. Furthermore, it is shown that the red light emission does not originate from energy transfer from a peroxidase substrate metabolite formed in the excited state. As chi-a has been widely utilized as a sensitizer for the detection of triplet excited species in various peroxidase-catalysed transformations in vitro and in vivo, the additional importance of this work is to show that the observation of red light emission in the presence of chi-a does not necessarily indicate the formation of triplet excited state substrate metabolites in peroxidase systems.