Marked slow-down of soluble sugar production at low degree of substrate conversion limits the spacetime yield of enzymatic hydrolysis of ligno-cellulosic materials. A simple set of kinetic descriptors was developed to compare reducing sugar release from pure crystalline cellulose (Avicel) and pretreated wheat straw by Trichoderma reesei cellulase at 50 degrees C. The focus was on the rate-retarding effect of maximum hydrolysis rate at reaction start (r(max)), limiting hydrolysis rate (r(lim)) at extended reaction time (24 h), and substrate conversion, marking the transition between the r(max) and r(lim) kinetic regimes (C-trans). At apparent saturation of substrate (12.2 g cellulose/L) with enzyme, r(max) for pretreated wheat straw (similar to 9.6 g/L/h) surpassed that for Avicel by about 1.7-fold whereas their r(lim), were almost identical (similar to 0.15 g/L/h). C-trans roughly doubled as enzyme/substrate loading was increased from 3.8 to 75 FPU/g, suggesting C-trans to be a complex manifestation of cellulase-cellulose interaction, not an intrinsic substrate property. A low-temperature adsorption step preceding hydrolysis at 50 degrees C resulted in enhanced cellulase binding at reaction start without increasing r(max). C-trans was higher for pretreated wheat straw (degrees 30%) than for Avicel (similar to 20%) under these conditions. (C) 2012 Elsevier Ltd. All rights reserved.