Literature on pectin degrading enzymes is reviewed. The enzymes involved in plant tissue maceration by Geotrichum candidum were investigated. Macerating activities from the culture filtrate of G. candidum were compared with those of Botrytis cinerea and Penicillium digitatum. Experiments were carried out to determine the optimum conditions for growth and production of pectic enzymes by G. candidum. Geotrichum strains from several sources were screened for high productivity of pectic enzymes. Acid soluble pectic acid, potato pectin, di- and tri-galacturonic acids were prepared in this laboratory for further enzyme assays. The actual uronic acid and methanol content of all enzyme substrates used in this work were determined experimentally. Polygalacturonase (PG) from G. candidum appeared unusual in causing tissue maceration at pH 2.0. The PG was successfully purified by 110 fold using ammonium sulphate fractionation followed by ion-exchange chromatography on CM-Sephadex C-50. The purified PG was characterized by pH optimum and stability; temperature optimum and stability; iso-electric point; electrophoretic homogeneity; moleculeir weight; the influence of cations, chelating agent, and pectins of varying degree of esterification on the enzyme activity; the action of PG on di- and tri-galacturonic acids and studies on the hydrolysis products of PG action on polygalacturonic acid. The production of pectic enzymes in vivo by G. candidum was briefly studied. A set of experiments was carried out to find support for a hypothesis which accounts for the mechanism of tissue maceration by purified Geotrichum PG at low pH.
|Date of Award||1974|