The identification of and relief from Fe3+ inhibition for both cellulose and cellulase in cellulose saccharification catalyzed by cellulases from Penicillium decumbens

► Cu2+ and Fe3+ inhibit cellulose hydrolysis catalyzed by P. decumbens cellulases. ► Fe3+ inhibition of cellulose hydrolysis takes place on both substrate and enzymes. ► Fe3+ treatment inhibits β-glucosidase activity more than pNPCase/CMCase activities. ► Inhibition of cellulose's digestibility is due to oxidation of the molecule. ► DTT and EDTA partially remove Fe3+ inhibition of cellulose hydrolysis.