Enzymes accumulated in plant cell walls serve diverse physiological functions including metabolism, polysaccharide structure modification, and molecular communication in interactions with other organisms. Pectin methylesterases are economically important enzymes for their impact on quality and processing properties of fruit and vegetable food products. We have now purified TT-PME to homogeneity from sweet orange finisher pulp and determined the complete corresponding nucleic acid sequence. Purified TT-PME was observed by SDS-PAGE as two doublet bands with molecular masses of approximately 46,000 Da and 56,000 Da. Direct Edman sequencing from these proteins showed a common N-terminal peptide. De novo sequencing of eight TT-PME tryptic peptides determined by MALDI-TOF/TOF mass spectrometry provided additional internal sequences. TT-PME did not correspond to any previously reported Citrus spp. PME sequence. Our results show Citrus TT-PME is a distinctive new isoform with phylogenetic relationship closer to PME isoforms in other species rather than to previously described Citrus PME genes.