Possible biochemical roles of oxalic acid as a low molecular weight compound involved in brown-rot and white-rot wood decays

Accumulation of oxalic acid in low nitrogen and high nitrogen nutrient cultures of brown-rot and white-rot fungi are compared with the previously reported findings on fungal production of oxalic acid. The enzymatic formation of oxalic acid from oxaloacetate and glyoxylate in brown-rot and white-rot fungi is described in comparison with other microorganisms. Possible biochemical roles of oxalic acid are discussed in relation to brown-rot and white-rot wood decays. In the brown-rot wood decay system, oxalic acid may serve as a proton source for enzymatic and non-enzymatic hydrolysis of carbohydrates and as a metal chelator. On the other hand, in the white-rot wood decay system, oxalic acid may play multiple roles, such as an inhibitior of lignin peroidases, an electron donor for producing NADH, which may be used for reduction of lignin derived quinones, a source of formate radicals to reduce dioxygen or ferric iron to yield superoxide anion radicals and ferrous iron, respectively, and a chelator for stabilization of manganic ions for lignin degradation. Similar roles of oxalic acid in other living organisms are also briefly described. (C) 1997 Elsevier Science B.V.