SOLUBILIZATION OF CELL WALLS BY TOMATO POLYGALACTURONASES: EFFECTS OF PECTINESTERASES

The susceptibility of isolated cell walls to solubilization by polygalacturonase and the effect of pectinesterase on the solubilization were examined. The two polygalacturonases in ripe tomatoes were purified to remove pectinesterase. Both polygalacturonases solubilized uronic acid from pectinesterase-free tomato cell walls most rapidly at about pH 3.5, well below p H 4.5, the pH optimum for their hydrolysis of pectic acid. At p H 3.5, very low levels of pectinesterase increased cell wall solubilization by the polygalacturonases seueralfold, whereas high concentrations of pectinesterase completely inhibited solubilization. A t pH 5, pectinesterase also increased cell wall solubilization, but higher concentrations were required than at pH 3.5 and high levels were not inhibitory. The materials solubilized at pH 3.5 were galacturonan with a molecular weight of about 110,000 and two fractions of much higher molecular weights consisting primarily of neutral sugars. Galactose accounted for about two-thirds of the monosaccharides in the neutral polysaccharides.