Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 16, 1995
Publication Date: N/A
Interpretive Summary: Pectinmethylesterase initiates a sequence of events that leads to precipitation of the juice cloud in fresh and under-pasteurized citrus juices. This enzyme also functions in plant cell growth, fruit softening and pathogenicity. A thermally tolerant pectinmethylesterase has been purified from a commercial 'Fresh Frozen Orange Juice' and thermally characterized. Data on molecular weight and glycosylation also are presented. Thermal characterization demonstrates that this pectinmethylesterase is extremely stable to heating, retaining 49.2 percent of its activity after a 60 sec treatment at 95 degrees C.
Technical Abstract: A thermally tolerant form of pectinmethylesterase (TT-PME) has been purified from a commercially available `Fresh Frozen Orange Juice' by gel filtration, heparin and concanavalin A chromatography. TT-PME represented 8.3 percent of total PME activity in the solubilized dialysis precipitate. This TT-PME retained 83.3 plus/minus 1.1% relative activity after a 2 min incubation in an 80 degree C water bath and 49.2 plus/minus 4.1% relative activity after a 60 sec incubation in a 95 degree C water bath. It also retained 3.3 plus/minus 0.6 percent and 8.3 plus/minus 1.5 percent relative activity at pH 3.5 and 4.5, respectively. It had a native molecular weight of 40.1 kDa (gel filtration chromatography) and a denatured Mr of 42.7 plus/minus 0.1. Binding to concanavalin A and treatment with PNGase F suggests it is an N-linked glycoprotein with 2 N-linked glycans. After extended deglycosylation with PNGase F polypeptide ebands at Mr 41.7 plus/minus 0.6 (n=4) and 40.1 plus/minus 0.4 (n=4) were observed.