FMN with Other Chain Components

FMN can perform the following functions. FMN accelerates the reaction of oxidation of lipids by air oxygen, and it increases the rate of the heterogeneous reaction of reduction of coenzyme Q by pyridine nucleotide. In discussing the biological significance of the first process, let us examine the electron transport reaction taking place in the membranes of mitochondria. It is known that electron transport in the initial part of the respiratory chain from 

NADH to ferricyanide, which proceeds effectively in aeorbic conditions, stops completely in anaerobic conditions. It could be supposed that in anaerobic conditions no peroxides necessary for electron transport are formed. Thus, it could be assumed that one of FMN s functions is that it maintains in mitochondrial membrane a certain optimal concentration of peroxide radicals, which are needed as catalysts of the electron transport reaction during respiration. It was shown that the formation of peroxides with the participation of FMN disappears in acid media. On the other hand, when peroxides are formed the layer adjacent to the membrane becomes enriched in protons. Hence, it follows that the peroxide formation process might possibly be a self-regulating one, the rate of which cannot rise endlessly. This circumstance once more substantiates the supposition that this process might play a very important functional role in membrane redox reactions. 

The experiments described above showed that in a system where NADH oxidation by oxygen proceeds chiefly on one side of the membrane, addition of the oxidizer KjFe(CN)6 on the other side of BLM (system 21) leads to a qualitative change in the process the reaction in the layer adjacent to the membrane is replaced by transmembrane electron transport (see Fig. 11). 

Consequently, it can be seen that depending on the ratio of the redox potentials in the solutions on either side of the membrane the examined electron transport chain can be located either on one side of the membrane, or directed across the membrane.  

Chlorophyll, which is responsible for photosensitisation during photosynthesis, itself undergoes redox transformation in the course of this process.  

POTENTIAL GENERATION ON BILAYER MEMBRANES CONTAINING CHLOROPHYLL 

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