Poster: Enzymology

Abs # 240: Isolation, Characterization and Pectin Modifying Properties of a Thermally Tolerant Pectin Methylesterase from Citrus sinensis var. Valencia

Presenter:	Cameron, Randall G, rcameron@citrus.usda.gov
Authors	Cameron, Randall G (A)   Savary, Brett J (B)   Hotchkiss, Arland T (B)   Fishman, Marshall L (B)   Chau, Hoa K (B)   Grohmann, Karel  (C)
Affiliations:	(A): USDA, ARS, South Atlantic Area, Citrus and Subtropical Products Laboratory, Winter Haven, FL 33881 (B): USDA, ARS, North Atlantic Area, Eastern Regional Research Center, 600 Mermaid Ln, Wyndmoor, PA 19038 (C): USDA, ARS, South Atlantic Area, Citrus and Subtropical Products Laboratory, Winter Haven, FL 33881 (Retired)

Numerous investigators have observed multiple forms of pectin methylesterase (PME) from an assorted variety of plant species. Recently, in addition to detailing physical and biochemical properties of PME, studies on this enzyme have included data on their affect on pectin physical properties and demethylation patterns. Four peaks of PME activity are distinguishable after heparin chromatography ofCitrus sinensisprotein extracts from fruit peel, rag tissue (intersegmental septa, squeezed juice sacs and fruit core tissue) or fruit juice. Three of these PMEs are thermally sensitive and one is thermally tolerant. Two of the thermally sensitive PMEs have been isolated and characterized. One was found to be salt independent (Type I PME, Peak 2) and the other was salt dependent (Type II PME, Peak 4). Both have been demonstrated to demethylate pectin in a blockwise fashion and to have no effect on pectin molecular weight. In this report we are presenting data on the thermally tolerant PME (Peak 3) from citrus fruit. We demonstrate it to have a molecular weight of approximately 37 kDa and a pI intermediate between the Peak 2 and Peak 4 PME. Its response to sodium chloride was intermediate to Peak 2 and Peak 4 PME. Its response to pH was salt dependent. At pH values of 6.5 and lower it behaved similar to the salt dependent PME and at higher pH values it behaved more similar to the salt independent PME. Additional data on kinetics, amino acid composition and resulting demethylation patterns also will be presented.