Influence of avocado (Persea americana) Cx-cellulase on the structural features of avocado cellulose

Abstract

Avocado (Persea americana Mill.) fruit produce copious quantities of the enzyme Cx-cellulase (EC 3.2.1.4) during ripening. The possibility that Cx-cellulase is able to disrupt cellulose microfibril oranization was investigated using molecular weight (Mr), x-ray diffraction, and ultrastructural analyses of cell walls from unripe avocado fruit incubated with the purified enzyme. Results indicate that Cx-cellulase causes a downshift in the Mr of unbranched cell-wall polymers in the Mr range of 106–107 Da. There is an increase in the proportion of crystalline cellulose, and cellulose fibrils appear to lose cohesiveness in response to enzyme activity. We propose that Cx-cellulase attacks avocado cellulose at accessible sites in the peripheral and integral noncrystalline regions of the microfibril, resulting in a loss of cohesiveness within the fibril structure and an alteration in the binding of associated cell-wall matrix polysaccharides. The initial loss of avocado mesocarp firmness during fruit ripening may be linked to the onset of Cx-cellulase activity.