ISHS Acta Horticulturae 398: Postharvest Physiology of Fruits
RHAMNOGALACTURONASE, α-GALACTOSIDASE, AND β-GALACTOSIDASE: POTENTIAL ROLES IN FRUIT SOFTENING |
| Authors: | K. C. Gross, David A. Starrett, H. Chen |
| Keywords: | Aspergillus aculeatus, Botrytis cinerea, Cell wall, Fruit softening, Fungal decay, Hydrolase, Polygalacturonase, Postharvest physiology |
| Abstract:
It is clear that neither polygalacturonase nor pectin methylesterase alone are responsible for tomato fruit softening. Other enzymes or factors must also be involved. It was recently reported that  -and  -galactosidase from avocado fruit solubilized tomato fruit pectin in vitro (DeVeau et al. 1993, Physiol Plant 87:279–285). In the present study, NaCl extraction of tomato pericarp yielded relatively high levels of -and -galactosidase activity. -Galactosidase was purified by multiple Mono Q and Superose 12 gel filtration HPLC. Gel filtration and SDS-PAGE suggested an apparent MW of 44 kD. The enzyme had a specific activity of 294 μmol product/min/mg protein, a Km of 317 μM, a pI of 5.0, and a pH optimum of 5.5. Activity was inhibited 67% by -D-galactose. -Galactosidase was purified using similar techniques with the addition of affinity chromatography on p-aminobenzyl l-thio--D-galactopyranoside.
We are also using heterologous cDNA clones from guar and carnation to screen a tomato fruit cDNA library for -and -galactosidase, respectively.
Rhamnogalacturonase, a recently identified hydrolase in Aspergillus aculeatus, can degrade the pectic backbone and is potentially important in fruit softening and fungal decay.
Previous methods used for rhamnogalacturonase assay in A. aculeatus involved methylation linkage analysis and gel filtration HPLC of oligomeric products.
We have developed a method for assaying RGase activity using | |
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