End products and mechanism of hydrolysis of pectin and pectic acid by yeast polygalacturonase (YPG)

Abstract

1. 1. The change in molecular weight of pectin (N.F.) due to the action of YPG has been studied. The weight-average molecular weight decreased from 56,200 to 15,100, and the number-average molecular weight dropped from 26,000 to 11,000. Good agreement was found between the extent of breakdown based on increase in reducing value and decrease in weightaverage molecular weight. 2. 2. At pH 5.0, pectic acid was found to be randomly hydrolyzed to a mixture of mono-, di-, and trigalacturonic acids. A procedure is described for the isolation of the last two acids in pure form. 3. 3. The naphthoresorcinol reagent is largely specific for monogalacturonic acid. In samples containing 50 μg., digalacturonic acid produces 7% of the color produced by monogalacturonic acid, trigalacturonic acid 3.5%, whereas tetragalacturonic acid and pectic acid give the same color as the blank. In mixtures with monogalacturonic acid, the interference appears to be somewhat less. 4. 4. During the initial very rapid rate of hydrolysis of pectic acid, in which about 25% of the glycosidic bonds are hydrolyzed, monogalacturonic acid does not appear in significant quantities as an end product. During the second slow phase in which the per cent hydrolysis increases to about 48, monogalacturonic acid formation roughly parallels the splitting of glycosidic bonds.