## 6 Properties of Fungal Biomass Degradation Hemi-Cellulaases and Cellulaases
(2019) study [45] was about 57-fold higher than the activity (0.0045 umol D-glucose/mg protein.min) determined with Avicel for the GH5 processive endoglucanase Cel5A in the brown rot basidomycete _Postia placenta_[118]. Several lines of evidence suggest that extracellular reactive oxygen species (ROS), specifically hydroxyl radicals produced from the Fenton reaction, play a compensatory biodegradable role in extensively disrupting crystalline cellulose in wood biomass in concert with their relatively weak and lack of activities of processive and non-processive endocellularases in the white and brown rot basidomycete fungi [112,119]. Last but not least, the white rot and the brown rot basidomycete fungi possess unique lignin-degradation enzymes [112]. Hence, low and lack of endocellase, especially the processive endocellase activities, are the recognized limiting enzymatic factors, and these basidomycete fungi are using ROS as recognized compensatory mechanisms in engaging effective lignocellulosic degradation of wood biomass materials. Giving the fact that lignin polymers further encapsulate microfibril units and reduce porosity of raw lignocellulosic biomass materials, possession of lignin-degradation enzymes by these fungi would facilitate their cellulases in effectively penetrating into the internal microfibrillar surface for effective hydrolysis. The most studied aerobic cellulosic microorganism is the fungus, _Hypocrea jecorina_, originally also called _Trichoderma viride_, and is renamed _Trichoderma reesei_ to honor Drs. [PERSON] and [PERSON] for their contributions in isolating this fungus during World War II [49]. _Trichoderma reesei_ fungi produce the two most abundant exocellulaes Cel7A (CBHI, making about 70% of the total cellulase proteins secreted) and Cel6A (CBHI, making about 10% of the total cellulase proteins secreted), as well as seven endoglucanas including Cel7B (EGI, the most abundant EG), Cel5A (EGII), Cel12A (EGIII, serving as expansin activity), Cel61A (EGIV), Cel45A (EGV), Cel5B and Cel61B [49]. Variable cellulase activities have been reported for various _Trichoderma reesei_ likely due to different research conditions such as enzyme purity, substrates and assay temperature. The two _Trichoderma reesei_ exocellulaes Cel7A (CBHI) and Cel6A (CBHI) activities were reported to be 0.0091 and 0.0085 umol D-glucose/mg protein.min, respectively, determined with filter paper [120]. However, these two _Trichoderma reesei_ exocellulaes Cel7A (CBHI) and Cel6A (CBHI) activities were reported to be 0.370 and 0.330 umol D-glucose/mg protein.min, respectively, determined with Avicel [121]. Meanwhile, an average _Trichoderma reesei_ endoglucanase (EG) activity at 0.420, and the _Trichoderma reesei_ Ce15A (EGII) activity at 0.0290 umol D-glucose/mg protein.min were determined with Avicel and filter paper by [PERSON] et al. [121] and [PERSON] et al. [122], respectively. Overall cellulase activities of the _Trichoderma reesei_ cellulase enzyme mixture products in hydrolyzing crystalline cellulose substrates (e.g., pretreated wood materials vs. Avicel), primarily marketed by Novozymes, were reported to be at 1.06 and 0.73 umol D-glucose/mg protein.min by [PERSON] and [PERSON] [123] and [PERSON] et al. [121], respectively. It is well established that endocellases and exocellulaes synergistically drive much higher specific enzyme activities for the _Trichoderma reesei_ cellulase enzyme mixture. Relatively high enzyme protein yield, high specific enzyme activity and a much-reduced enzyme production cost by about 10-fold in recent years are the main reasons that the _Trichoderma reesei_ cellulase enzyme mixture is the primary cellulase product on the current market [48,50]. Another aerobic fungus used for industrial cellulase production is _Humicola insolens_ that produces a similar set of multiple endocellases and exocellulaes but with a much lower enzyme protein yield and specific activities [49,50].