Blue radicals flavoproteins

Protein fixation . Massey et al. (121) were the first to investigate systematically bioradical formation by comparative enzymology of flavoproteins . It turned out that flavoproteins can be divided into two classes according to whether their radicals are blue or red. Moreover and quite surprisingly, it became obvious that all red radical flavoproteins were 2/2-flavoproteins (Table 1, cf. above), while the blue radical flavoproteins happened to be either 1/1-, 2/1- or 1/2-flavoproteins. In other words All flavoproteins involved essentially with le -transfer (either by input or by output or by both) have blue radicals. Massey and Palmer referred to the blue radical flavoproteins as dehydrogenases and to... 

The 1/1-flavoproteins, i.e. the well-known flavodoxins, are not dehydrogenases — and still they are blue radical flavoproteins . 

Hence, the term electron transferases as contrasted with oxidases appears preferable over dehydrogenases for the blue radical flavoproteins (80). 

Two ascorbate radicals can react with each other in a disproportionation reaction to give ascorbate plus dehydroascorbate. However, most cells can reduce the radicals more directly. In many plants this is accomplished by NADH + H+ using a flavoprotein monodehydroascorbate reductase.0 Animal cells may also utilize NADH or may reduce dehydroascorbate with reduced glutathione.CC/ff Plant cells also contain a very active blue copper ascorbate oxidase (Chapter 16, Section D,5), which catalyzes the opposite reaction, formation of dehydroascorbate. A heme ascorbate oxidase has been purified from a fungus. 11 1 Action of these enzymes initiates an oxidative degradation of ascorbate, perhaps through the pathway of Fig. 20-2. 

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