Polygalacturonase from Citrus Fruit Infected withPenicillium italicum

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Abstract
An endo-polygalacturonase (E.C. 3.2.1.15) (endo-PG) was isolated and purified from grapefruit (Citrus paradisi) peel infected with P. italicum. The estimated MW of the endo-PG was 36,000 daltons and it had optimum activity at pH 5.0. Citrus pectin and sodium polypectate (NaPP) were degraded by the enzyme, but NaPP was the most readily degraded. The purified enzyme macerated citrus mesocarp in vitro. The fresh weight (.mu.eq/g) of diffusible free organic acid was 70.0 for decayed peel and 6.7 for healthy peel. Galacturonic acid in the decayed peel averaged 8.6 mg/g fresh wt. Plasmolysis, cell wall swelling, and degradation of the wall at the site of hyphal penetration were associated with invading hyphae. Dissolution of the middle lamella by the endo-PG is a major factor contributing to hyphal penetration.