Isolation, characterization, and pectin-modifying properties of a thermally tolerant pectin methylesterase from Citrus sinensis var. Valencia.
The thermally tolerant pectin methylesterase (TT-PME) was isolated as a monocomponent enzyme from sweet orange fruit (Citrus sinensis var. Valencia). It was also isolated from flower and vegetative tissue. The apparent molecular weight of fruit TT-PME was 40800 by SDS-PAGE and the isoelectric point estimated as pI 9.31 by IEF-PAGE. MALDI-TOF MS identified no tryptic-peptide ions from TT-PME characteristic of previously described citrus PMEs. TT-PME did not absolutely require supplemented salt for activity, but salt activation and pH-dependent activity patterns were intermediate to those of thermolabile PMEs. Treatment of non-calcium-sensitive pectin with TT-PME (reducing the degree of methylesterification by 6%) increased the calcium-sensitive pectin ratio from 0.01 to 0.90, indicating a blockwise mode of action. TT-PME produced a significantly lower end-point degree of methylesterification at pH 7.5 than at pH 4.5. Extensive de-esterification with TT-PME did not reduce the pectin molecular weight or z-average radius of gyration, as determined by HPSEC.
Cameron
Randall G
RG
Quality Improvement in Citrus and Subtropical Products Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 600 Avenue S N.W., Winter Haven, Florida 33881, USA. rcameron@citrus.usda.gov
Savary
Brett J
BJ
Hotchkiss
Arland T
AT
Fishman
Marshall L
ML
D002265:Carboxylic Ester Hydrolases / Q000302:isolation & purification* / Q000378:metabolism*; D032084:Citrus sinensis / Q000201:enzymology*; D005638:Fruit / Q000201:enzymology; D006358:Hot Temperature; D010368:Pectins / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry
D010368:Pectins; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase