The Hydrolysis of Pectic Acid by Purified Fungal Polygalacturonase

Abstract

Although the enzymatic hydrolysis of pectic substances has been under investigation for a considerable time, and some aspects of its mechanism are known, the nature of this hydrolysis is not yet fully elucidated (7,9). Most of the data on the hydrolysis of 1,4glycosidic bonds of polygalacturonic acid preparations have been obtained with crude or at most partially purified polygalacturonases from commercial fungal enzymes. Jansen and MacDonnell ( 4 ) showed that polygalacturonase ( P G ) obtained from Pectinola preparations and free from pectin esterase ( P E ) will hydrolyze pectic acid rapidly, but its rate of hydrolysis of pectinic acids of varying degree of esterification with methyl alcohol decreases with increase in esterification. They explain the differences in rate of hydrolysis and in extent of hydrolysis by postulating that both the carbonyl groups adjacent to a 1,4-linkage must be free for it to be labile to PG. Matus (Zl), however, reported extensive glycosidic splitting of highly esterified pectic acids by crude PG preparations obtained from Swiss commercial filtration enzyme preparations. The hydrolysis of pectic acid by PG preparations from Pectinols has been followed usually by determination of decrease in viscosity and increase in free aldehyde groups ; these preparations are characterized by extensive decrease in viscosity (of the order of magnitude of 50%) when the extent of hydrolysis as measured by increase in reducing power is 2% or slightly less (4,7,9,10). Hydrolysis apparently occurs by random scission of the glycosidic linkages of pectic acid leading to the accumulation of D -galacturonic acid. By the application of chromatographic methods, compounds intermediate between pectic acid and D-galacturonic acid have been detected during the course of hydrolysis of pectic acid by PG preparations from three different molds ( 6 ) , and also of pectinic acid by commercial pectic enzyme preparations (16). The formation of lower molecular weight products of hydrolysis has been demonstrated, also by the use of ion exchange resins ( 3 ) . The polygalacturonase of Neurospora Grassa has been recently shown to convert more than 50% of the pectic acid hydrolyzed to a low molecular weight polyuronide (M W ca. 4,000), (18) ; di-and tri-galacturonic acids have been isolated among the end products of hydrolysis of pectic acid by the polygalacturonase of Saccharomyces fragilis (13) and also by a commercial fungal preparation (1). Fungal preparations thus may differ in their content of PE, and contain more than one PG enzyme (pectin depolymerase as well as pectin polygalacturonase).Since but little information was available in 1948 at the start of our investigations (14) on the course of hydrolysis of well defined pectic acid "Commercial pectic enzyme preparations manufactured by Rohm and Haas Company, Philadelphia, Pennsylvania. 308

Damage-associated responses of the host contribute to defence against cyst nematodes but not root-knot nematodes

“…PGs are key enzymes that cleave the α1–4 linkage between the d -galacturonic acid residues of homogalacturonan ( Kalunke et al , 2015 ; Rahman and Joslyn, 1953 b ; Themmen et al , 1982 ). PGs are well characterized in fungi, bacteria, and insects, and their action on the outer plant cell wall is essential for further wall degradation by other wall-degrading enzymes ( Rahman and Joslyn, 1953a, b ; Kester and Visser, 1990 ). Several fungi secrete PGs, including Aspergillus flavus ( Whitehead et al , 1995 ), Botrytis cinerea ( Cabanne and Doneche, 2002 ; Favaron et al , 1992 ), Aspergillus niger ( Maldonado and de Saad, 1998 ), Claviceps purpurea ( Oeser et al , 2002 ), and Sclerotinia sclerotiorum ( Reymond-Cotton et al , 1996 ).…”

Properties of Purified Fungal Polygalacturonase

“…The results of older investigations ( 4 ) on pH optima, stability, and activation by alkali salts are subject to errors arising from the use of ill-dehed substrates and of preparations containing pectin esterase (PE ) as well as pectin polygalacturonase (PG) . The effect of several factors on the activity of purified PG prepared from three commercial fungal sources is presented here j the investigations in more detail have been reported by Rahman (11). EXPERIMENTAL Source and purification of polygalacturonases.…”