15B-1 |
Purification and characterization of a salt-dependent pectin methylesterase from Citrus sinensis var. Valencia fruit rag tissue |
R. G. CAMERON1, K. Grohmann1, B. J. Savary2, and R. A. Baker1. (1) Citrus & Subtropical Products Lab., USDA-ARS-South Atlantic Area, PO Box 1909, Winter Haven, FL 33883, (2) USDA-ARS-Eastern Regional Research Center, 600 E. Mermaid Ln., Wyndmoor, PA 19038-8598 Pectin methylesterase (PME) initiates a sequence of events resulting in juice-cloud precipitation in improperly stabilized and handled citrus juices. Multiple forms of PME present in citrus juice, peel and rag have differential effects on juice cloud stability with one form having no effect. These observations suggest that they may have a differing modes of action on pectin. To determine their mode of action each form must be purified and characterized before its mode of action can be ascertained. A PME (PME 4) from Citrus sinensis var Valencia mature fruit rag tissue (intersegmental septa, squeezed juice sacs and fruit core tissue) has been purified. DEAE, heparin and gel filtration chromatography were utilized. At pH 7.5 the enzyme elutes from the Heparin Sepharose CL-6B column with approximately 0.2 - 0.25 M NaCl. Denaturing electrophoresis indicates a molecular mass of approximately 32 kDa. The enzyme is salt-dependent with no activity in the absence of cations. The requirement for relatively high salt concentration for elution from Heparin and its requirement of salt for activity suggest it is similar to the fruit-specific PME isolated from tomatoes. Further characterization will aid in ascertaining its similarity to this and other forms of PME as well as its inability to destabilize citrus juice cloud.
Session 15B, Citrus
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