Sunday, April 29, 2007

Endogenous cellobiase activity in maize kernels is potentially a useful adjuvant to heterologously-expressed cellulases

John O. Baker1, Eric P. Knoshaug2, Tina Jeoh1, William Michener2, William S. Adney1, and Michael E. Himmel1. (1) Chemical and Biosciences Center, National Renewable Energy Laboratory, 1617 Cole Blvd, Lakewood, CO 80401-3393, (2) National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401-3393

Mature, but unsprouted maize kernels have been found to contain tightly-bound general β-glucosidase activity that shows quite significant activity against cellobiose, in addition to releasing fluorescent products from common fluorogenic glucosidase substrates such as 4-methylumbelliferyl-β-D-glucoside.  Apparently as a result of sequential cleavages on the same substrate molecule, the activity can also produce fluorescence from supposed “cellobiohydrolase and endoglucanase substrates” such as 4-methylumbelliferyl-β-D-cellobioside and 4-methylumbelliferyl-β-D-lactoside. While this latter endogenous fluorogenic activity will present an analytical interference to researchers attempting to track cellulases heterologously expressed and packaged in maize kernels, the activity against cellobiose can also constitute a valuable bonus for ultimate users of the expressed cellulases in that it can potentially replace cellobiase activity that might otherwise have to be produced and added separately to cellulose-saccharification mixtures in order to maximize effectiveness of the endoglucanases and cellobiohydrolases.  The properties of the endogenous maize cellobiase, in both bound and extracted forms, are discussed in terms of its utility in saccharification processes.  This abstract is subject to government rights.