Fluctuations in activities of three β-galactosidase isoforms from ripening avocado (Persea americana) fruit and their different activities against its cell wall polysaccharides as substrates

Abstract

Since there is little information about the relationship between glycosidases and avocado fruit softening, we assayed some glycosidase activities during avocado fruit softening. β - Galactosidase, α - L - arabinofuranosidase and β - glucosidase activities increased during ripening; that of β - galactosidase activity closely paralleled the trend in fruit softening. Therefore, β-galactosidase was fractionated into three isoforms using hydrophobic chromatography and cation exchange chromatography; the isoforms were labeled AV - GAL I, AV - GAL II or AV - GAL III. AV - GAL III activity in the fruit, which was detected 4 days after harvest, increased with fruit softening, whereas AV - GAL I and II activities were detectable throughout the ripening period with little change. When the activities against four fractions of cell wall polysaccharides prepared from avocado fruit were assayed, AV - GAL III released a significant amount of monomeric D-galactose from guanidine thiocyanate (GTC) soluble cell wall polysaccharide, compared with AV - GAL I and II. AV - GAL I did not release detectable D-galactose from the four isolated cell wall polysaccharides, indicating that, among three β - galactosidase isoforms, AV - GAL III plays the most important role on the softening of avocado fruit.