From: Biochemistry (Moscow), Vol. 61, No. 7, 1996, pp. 837-844. Translated from Biochimiya, Vol. 61, No. 7, 1169-1181. The Role of Electron Excited States in Biochemical Processes. I.V. Baskakov, V.L.Voeikov Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Miklukho-Maklaya 16/10, 117871, Moscow, Russia Department of Bioorganic Chemistry, M.V.Lomonosov Moscow State University. Abstract. Oxidative processes major sources of energy accumulated in macroergic bonds of ATP. A part of the energy produced in redox reactions is transformed into the energy of electron excitation of the corresponding reaction products. Recently much experimental evidence has been obtained that confirms that the energy of electron excitation of such products may be used for high energy processes, photomodulation of enzyme activity, etc. The review describes some enzymatic and non-enzymatic biochemical processes generating electron excited states, potential pathways of radiation-less energy transduction, and examples of reactions coupled to these energy sources. The main attention is paid to triplet electron excited species because they are most probable participants of biochemical reactions. Numerous experimental data on "photobiochemistry without light" suggest that the processes generating electron excited states can be considered as one of the energy sources for certain cellilar biochemical reactions. Processes of photochemical coupling in the dark are compared with the electrochemical coupling that is the basis of cellular respiration. Unlike processes that use ATP as an energy source, photochemical coupling in the dark provides much more high energy.