The activities of both cellulase and pectinase have been observed to increase during
ripening of avocado fruits and result in their softening. Cellulase is an enzyme with a relative
molecular mass of 54.2 kDa and formed by extensive posttranslational processing
of a native 54-kDa protein involving proteolytic cleavage of the signal peptide and glycosylation
(Bennet and Christofferson, 1986). Further studies have shown three isoforms of
cellulose ranging in molecular masses between 50 and 55 kDa. These forms are associated
with the endoplasmic reticulum, the plasma membrane, and the cell wall (Dallman et al.,
1989). The cellulase isoforms are initially synthesized at the style end of the fruit at the
initiation of ripening, and the biosynthesis moves toward the stalk end of the fruit with the
advancement of ripening. Degradation of hemicelluloses (xyloglucans, glucomannans, and
galactoglucomannans) is also considered as an important feature that leads to fruit softening.
Degradation of these polymers could be achieved by cellulases and galactosidases