Enzymes humic substance formation

MnP is the most commonly widespread of the class II peroxidases [72, 73], It catalyzes a PLC -dependent oxidation of Mn2+ to Mn3+. The catalytic cycle is initiated by binding of H2O2 or an organic peroxide to the native ferric enzyme and formation of an iron-peroxide complex the Mn3+ ions finally produced after subsequent electron transfers are stabilized via chelation with organic acids like oxalate, malonate, malate, tartrate or lactate [74], The chelates of Mn3+ with carboxylic acids cause one-electron oxidation of various substrates thus, chelates and carboxylic acids can react with each other to form alkyl radicals, which after several reactions result in the production of other radicals. These final radicals are the source of autocataly tic ally produced peroxides and are used by MnP in the absence of H2O2. The versatile oxidative capacity of MnP is apparently due to the chelated Mn3+ ions, which act as diffusible redox-mediator and attacking, non-specifically, phenolic compounds such as biopolymers, milled wood, humic substances and several xenobiotics [72, 75, 76]. 

The polymerisation of phenolic acids is an oxidative process which may be catalysed by enzymes such as phenolase and peroxidase, as well as by inorganic soil components. The enzymic polymerisation of phenolic compounds, studied extensively by Flaig, Martin, Haider and their co-workers, in the context of the formation of humic substances, has been reviewed by... 

Tatsumi, K., S. Y. Liu, and J. M. Bollag. 1992. Enzyme-catalyzed complex formation of chlorinated anilines with humic substances. Water Sci. Technol. 25 57-60. 

---