One-electron reduction pathway

It is possible to reduce enzymatically both AFR and DHA, regenerating ascorbate and thus decreasing nutritional requirements in animals unable to carry out the synthesis de novo. Enzymatic systems that reduce AFR usually utilize NADH as an electron donor (one-electron reduction pathway or NADH-ascorbate free radical reductase). Reduction of DHA to ascorbate involves two electrons and has been attributed to thioltransferase (glutaredoxin) and protein disulfide isomerase (Wells et aL, 1990). However, taking into consideration the reported values for DHA (millimolar range) it is unlikely that the latter enzymes are involved in the maintenance of ascorbate in its reduced state in vivo and that function is carried out by NADH-AFR reductase (Minetti et aL, 1992). 

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