ONE-ELECTRON-TRANSFER REACTIONS IN BIOCHEMICAL SYSTEMS .2. REACTION OF FREE RADICALS FORMED IN ENZYMIC OXIDATION

Free radicals formed in the enzymic oxidation are extremely reactive and act as strong reductants or oxidants. The rate constants of the reaction of free radicals with cytochromes are measured directly using an electron spin resonance (ESR) spectrometer and a sensitive spectrophotometer, both equipped with a flow apparatus. 2-Methyl-1,4-naphthosemiquinone (MKH), for instance, is a very active reductant and reduces cytochrome c and cytochrome b5. THe rate constants are about 3·108 M-1. sec-1. MKH is also found to react with molecular oxygen at a rate constant of roughly 5·106 M-1·sec-1. The rate constants of cytochrome c reduction by monodehydroascorbate and p-benzosemiquinone are measured directly as 4.0·104 and 2.5·106 M-1. sec-1, respectively. On the other hand, free radicals derived from p-cresol and chlorpromazine act as effective one-electron oxidants. The one-electron transfer from donor molecules to these free radicals is confirmed by means of ESR spectroscopy. © 1969.