Abstract
This contribution reports on the thermodynamics of free radical reactions and the maintenance of cell redox homeostasis. Attention is focused on the definition of the half-cell reduction potential and the reducing capacity of the antioxidant couples, the cellular defence system substantiated by the thioredoxin, NADP(H), ascorbic acid, and thiol-containing molecules including glutathione (GSH), cysteine and protein thiols. Triggering of the signalling processes in the cell require the action of the electrochemical potential gradients of the corresponding redox pairs. Experimental quantification of electrochemical potential gradients of the corresponding redox pairs is briefly discussed.