Pectin Methyl Esterase
(Pectin pectyl hydrolase EC 18.104.22.168)
Pectin methylesterase (PME) (Pectase or pectinesterase) deesterifies pectin into pectic acid and methanol and thus makes it susceptible to precipitation by calcium or other polyvalent cations. The roots, stem, leaves and fruits of most higher plants contain PME.
Since PME produces methanol and free carboxyl groups in pectic acid, either methanol or the carboxylic group may be measured as a function of the enzyme.
» Solid salt mixture of NaCl and EDTA disodium salt 10:1, (w/w)
» Salt Mixture Solution
Dissolve 7.5g of the above mixture in 100mL water.
Prepare 2% (w/w) pectin solution in 1.5M NaCl. From this stock solution, dilute accordingly to get 1% solution in 0.1M NaCl.
» 0.1N or 0.02N NaOH. For low enzyme activities use dilute alkali.
» Enzyme Extract
To about 30g macerated tissue add 2.25g NaCl-EDTA salt mixture and stir for 15 min and centrifuge. Collect the supernatant. Again stir the residue with 20mL of salt mixture solution for 15min, centrifuge and collect the supernatant. Repeat the extraction step. To the supernatant collected each time, add 100mL cold ethanol and collect the precipitate. Pool the precipitate, dissolve in 1.5M NaCl and use as enzyme source.
One unit of pectin methylesterase activity is that amount of enzyme; which releases one milliequivalent of carboxyl groups per min per g sample. Milliequivalent of carboxyl group is calculated by multiplying titre value with the normality of the alkali used.
1. Hobson, G E (1964) Biochem J 92 304.
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