BINDING REVERSIBILITY AND SURFACE EXCHANGE OF THERMOMONOSPORA-FUSCA E-3 AND E-5 AND TRICHODERMA-REESEI CBHI

The sorption of Thermomonospora fusca E-3 and E-5 and Trichoderma rees ei CBHI cellulases on bacterial microcrystalline cellulose (BMCC) was investigated to measure binding reversibility and surface exchange. Th e adsorption and desorption curves for CBHI were comparable; this sugg ests a totally reversible binding process. By contrast, the desorption isotherms of E-3 and E-5 did not retrace their respective adsorption curves; instead, hysteresis loops were formed. The calculated percent reversibilities for E-3, E-5, and CBHI were 73 +/- 7%, 80 +/- 7%, and 95 +/- 7%, respectively. Surface exchange studies indicated that the a dsorbed and free cellulases were exchanging at the cellulose surface. Despite this confirmation of molecular exchange, the extent of exchang e did not reach the level that would be predicted if the preadsorbed c ellulase were to equally redistribute between the free and bound state s. The percent of exchange for E-3 and E-5 decreased with increasing i nitial total cellulase concentration (E-t) while that for CBHI showed no dependence on E-t. (C) 1997 by Elsevier Science Inc.