We previously reported that benzo-(a)-pyrene (BP) and methylcholanthrene (MC) emitted blue-colored ultra-weak chemiluminescence (CL) during the metabolism in a post mitochondrial fraction system. In this present study, we used a single-photon counting system (SPC) equipped with a photomultiplier having a spectral response in the red-color region to detect the CL from BP, MC, and 3-nitrofluoranthene (3-NF). As a result, we discovered that a novel red-region CL was emitted immediately after initiation of the metabolic reaction in this system. In the case of BP and MC, each had a double phase CL emission; that is, they initially emitted red CL, which was detected by the SPC, and thereafter, blue CL, which was detected with an OX-71 chemiluminescence analyzer. However, in the case of 3-NF, although strong red CL emission was recorded, no blue-colored CL appeared to be emitted. The emissions of red CL were increased in systems in which D20 was added (final concentration of 66%), and decreased by the addition of β-carotene or α-tocopherol. This result suggests that the main cause of CL was singlet oxygen.
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