CHEMI-LUMINESCENCE OF ACANTHAMOEBA-CASTELLANII

Chemiluminescence of Acanthamoeba castellanii in the presence of O2 was of similar intensity in organisms harvested early or late during exponential growth [when cyanide (1mM) stimulates or inhibits respiration respectively]. Cyanide (up to 1.5 mM) stimulated photoemission in both types of organism by 250-300 photons/s per 107 cells above the value observed under aerobic conditions. 'Dibromothymoquinone' (2,5-dibromo-6-isopropyl-3-methyl-p-benzoquinone) (up to 80μM) further increased chemiluminescence. Similar responses were also demonstrated in whole homogenates and in subcellular fractions; 36% of the chemiluminescence was provided by a fraction sedimenting at 100,000g-min, and 20% in that fraction that was non-sedimentable at 200,000g-min. Mitochondrial substrates (succinate, 2-oxoglutarate, NADH) in the presence or absence of ADP and P(i) or peroxisomal substrates (glycollate, urate or ethanol) gave no increases in light emission by whole homogenates or in any of the fractions. It is suggested that reactions responsible for production of chemiluminescence are those primarily producing superoxide anions and leading to lipid peroxidation and singlet-oxygen formation. Photoemission enhancement and superoxide dismutase inhibition showed similar cyanide concentration-dependencies.