Zm. Ali et al., ISOLATION, CHARACTERIZATION AND SIGNIFICANCE OF PAPAYA BETA-GALACTANASES TO CELL-WALL MODIFICATION AND FRUIT SOFTENING DURING RIPENING, Physiologia Plantarum, 104(1), 1998, pp. 105-115
beta-Galactosidases (EC 3.2.1.23) from ripe papaya (Carica papaya L. c
v. Eksotika) fruits having galactanase activities were fractionated by
a combination of cation exchange and gel-filtration chromatography in
to three isoforms, viz., beta-galactosidase I, II and III. The native
proteins of the respective isoforms have apparent molecular masses of
67, 67 and 55 kDa, each showing one predominant polypeptide upon SDS-P
AGE of about 31 and 33 kDa for beta-galactosidases I and III, respecti
vely, and of 67 kDa for beta-galactosidase II. The beta-galactosidase
I protein, which was undetectable in immature fruits, appeared to be s
pecifically accumulated during ripening. The beta-galactosidase II pro
tein was present in developing fruits, but its lever seemed to decreas
e with ripening. beta-Galactosidase I seemed to be an important soften
ing enzyme; its activity increased dramatically (4- to 8-fold) to a pe
ak early during ripening and correlated closely with differential soft
ening as related to position in the fruit tissue. The inner mesocarp t
issue was softer, and its wall pectins were modified earlier and firmn
ess decreased more rapidly during ripening compared to the outer mesoc
arp tissue. beta-Galactosidase II also may contribute significantly to
softening because of its ability to catalyse increased solubility and
depolymerization of pectins as well as through its ability to modify
the alkali-soluble hemicellulose fraction of the cell wall. The physio
logical significance of both beta-galactosidase isoforms may partly be
attributed to their functional capacity as beta-(1,4)-galactanases.