Very recently, some researchers have also suggested a nonneglectable
effect of accessory enzymes made in measuring the
enzyme activity with the model substrate [2,16,17]. And the existence
of accessory enzymes resulted in a significant deviation
at real hydrolytic efficiency of cellulase preparations from the
standardized assay. Kabel et al. [16] showed that the activity
analyzed in the standard cellulase/xylanase test did not present
a high correlation with the corresponding components degradation
of wheat bran and grass. Several commercial cellulase
preparations exhibited different degradations on wheat bran/grass
cellulose as they had different accessory enzyme activities. Likewise,
it was concluded by Pryor and Nahar [17] that the accessory
enzyme (i.e., inherent xylanase and pectinase) activities were at
least one of the main reasons that standardized protocols for
measuring enzyme activity are not adequate for assessing activity
using pretreated lignocellulosic substrates. Notably, Berlin
et al. evidenced the active role of accessory enzymes in cellulase
hydrolysis of natural lignocellulosic substrates, arguing that the
enzyme preparations with similar cellulase activity would show
differences in performance on lignocellulose if they differ in accessory
enzyme composition [2,15]. Considering that the commonly
used filter paper activity defines a combination of the endoglucanase,
the cellubiohydrolase and at most the -glucosidase
activities, some activities of accessory enzymes/proteins cannot
be measured by the standardized FPA assay. It is logic
to infer that these accessory enzymes should have exerted an
active role in the cellulase activity assay, which is neglected by
FPA.