There are a large number of cellulosic substrates that are used in the laboratory to assay cellulase reactivity (Table 2). Cellulose is synthesized by plants, and some algae, bacteria, and fungi. In plants, cellulose microfibrils may be covered by hemicellulose polymers and lignin matrices [69]. Cellulose chains from plant fibers typically have a degree of polymerization (DP) of 300-10,000 glucosyl subunits [37]. Although direct assay of deconstruction of native lignocellulosic materials such as corn stover and sugarcane bagasse would be ideal for large-scale biofuel production, cellulase activity is more easily studied using simpler substrates that are enriched in the cellulosic fraction. Moreover, it is often preferable to perform cellulase assays with substrates that have been modified (either noncovalently or covalently) to enhance accessibility, uniformity, or solubility. The substrates listed in Table 2 are commercially available or can be prepared from commercial material by simple pretreatment steps.

End endocellulase; Exo exocellulase; fi-Gluc b-glucosidase activity a DP, degree of polymerization b CR, crystallinity (percentage)

cAssay, type of activity most easily measured with a given substrate d Data from Zhang et al. [81] e Data from Park et al. [55] fData from Valjamae et al. [74]

8 Data from Stalbrand et al. [67] h Data from Zhang et al. [82]