No abstract

The impact of lignins of various origins on filter paper hydrolysis by fungal cellulase was evaluated. Powdered lignins were added to enzyme incubations, either as isolated or after thorough hydroxypropylation of phenolic sites. Extent of cellulose hydrolysis was reduced by 14−60% by the addition of up to 15% lignin to the substrate. Unmodified lignins were more detrimental to cellulose hydrolysis than hydroxypropylated lignins. The inhibitory effect of lignin addition was only partially overcome by a 10-fold increase in cellulase activity, suggesting inhibitory lignin interactions with both substrate and enzyme. Preincubation of cellulase with underivatized lignins resulted in reduced enzyme activity and soluble protein concentration in the supernatant, suggesting protein precipitation with lignin rather than reduced activity of a lignin−enzyme complex as the inhibitory mechanism. Two further experiments showed that the negative impact of lignin on cellulose hydrolysis can be counteracted by addition of various N compounds and by ammoniation. Keywords: Lignin; cellulose degradation; cellulase inhibition; free phenolic group; ammoniation; PEG; PVP; N compounds

The phenylpropanoid pathway is responsible for the synthesis of a large range of natural products in plants, including flavonoids (pigments and UV protectants), the structural polymer lignin, and antimicrobial furanocoumarin and isoflavonoid phytoalexins (Hahlbrock and Scheel, 1989; Dixon and Paiva, 1995). Salicylic acid, which is involved in the establishment of both local and systemic plant defense responses, is also a product of this pathway (Klessig and Malamy, 1994). Although the importance of phenylpropanoid natural products makes the pathway an obvious target for plant improvement by metabolic engineering, little is known about the control of flux into the various branches of the pathway. Many phenylpropanoid