8. POLYSACCHARIDASES
405
the enzymes are actually secreted by the snail or formed by the fauna
of the digestive tract.
In the vegetable kingdom, pectic enzymes have been found in higher
plants, i.e., in tomatoes (298, 299) and in germinated barley (300), rye,
oats, as well as in fruits, e.g., apples, pears, and peaches. Kertesz
(294), however, states that "it appears that the enzyme might not be
present in fruits as commonly as it was formerly assumed."
In lower plant life, pectic enzymes are very common. They occur
in algae (Thallophyta) (301); in bacteria (302), e.g., in Bacillus
carotovorus, B. cannabinus, B. amylovorus, Pseudomonas solanacearum,
etc. (303); and in molds, e.g., in Myrothecium verrucaria, Sclerotinia
Ubertiana, Botrytis cinerea, Rhizopus tritici, Aspergillus oryzae, Fusarium
chromiophthoron, etc. (302).
c. Properties. The presence of methyl ester groups in protopectin,
pectinic acids, and pectins appear to have an unfavorable influence on
the action of the glycosidic linkages splitting pectic enzymes. Although
pectic acids are most readily split, esterification of the carboxyl groups
with ethylene oxide gradually reduces the enzymatic availability of the
modified substrate, and completely esterified pectic acid glycolate is
enzyme resistant (304).
Purified polygalacturonase was found to be highly specific (305);
starch, maltose, sucrose, oxidized cellulose, carboxymethylcellulose, inulin, and ovomucoid were not measurably attacked by the enzyme.
Even a large number of uronic acid-containing polysaccharides, such as
gum arabic, gum ghatti, mesquite gum, gum tragacanth, alginic acid,
and pneumococcus polysaccharide type I did not act as substrates, nor
were methyl galacturonide and its methyl ester hydrolyzed by this
enzyme. Mucopolysaccharides like hyaluronic acid and heparin were
equally not attacked by the same enzyme preparations.
Polygalacturonases from molds are activated by many salts, especially
by chlorides (306), and the activation power increases in the following
sequence Li < Na < K < Rb < Cs. This property has certain analogies
to the activation of animal amylases by sodium chloride.
4. Pectic Enzymes That Hydrolyze Methyl Ester Bonds
a. Methods of Activity Determination. The assay of pectinesterase
can be accomplished either by the determination of the amount of
methanol liberated (307, 308) or by direct titration of the increase in
carboxyl groups (309). In both cases, pectinic acid serves as a substrate.
b. Occurrence. Pectinesterase has not been reported to occur in the
animal kingdom, but this enzyme is widely distributed in higher plants
and in molds.
405
the enzymes are actually secreted by the snail or formed by the fauna
of the digestive tract.
In the vegetable kingdom, pectic enzymes have been found in higher
plants, i.e., in tomatoes (298, 299) and in germinated barley (300), rye,
oats, as well as in fruits, e.g., apples, pears, and peaches. Kertesz
(294), however, states that "it appears that the enzyme might not be
present in fruits as commonly as it was formerly assumed."
In lower plant life, pectic enzymes are very common. They occur
in algae (Thallophyta) (301); in bacteria (302), e.g., in Bacillus
carotovorus, B. cannabinus, B. amylovorus, Pseudomonas solanacearum,
etc. (303); and in molds, e.g., in Myrothecium verrucaria, Sclerotinia
Ubertiana, Botrytis cinerea, Rhizopus tritici, Aspergillus oryzae, Fusarium
chromiophthoron, etc. (302).
c. Properties. The presence of methyl ester groups in protopectin,
pectinic acids, and pectins appear to have an unfavorable influence on
the action of the glycosidic linkages splitting pectic enzymes. Although
pectic acids are most readily split, esterification of the carboxyl groups
with ethylene oxide gradually reduces the enzymatic availability of the
modified substrate, and completely esterified pectic acid glycolate is
enzyme resistant (304).
Purified polygalacturonase was found to be highly specific (305);
starch, maltose, sucrose, oxidized cellulose, carboxymethylcellulose, inulin, and ovomucoid were not measurably attacked by the enzyme.
Even a large number of uronic acid-containing polysaccharides, such as
gum arabic, gum ghatti, mesquite gum, gum tragacanth, alginic acid,
and pneumococcus polysaccharide type I did not act as substrates, nor
were methyl galacturonide and its methyl ester hydrolyzed by this
enzyme. Mucopolysaccharides like hyaluronic acid and heparin were
equally not attacked by the same enzyme preparations.
Polygalacturonases from molds are activated by many salts, especially
by chlorides (306), and the activation power increases in the following
sequence Li < Na < K < Rb < Cs. This property has certain analogies
to the activation of animal amylases by sodium chloride.
4. Pectic Enzymes That Hydrolyze Methyl Ester Bonds
a. Methods of Activity Determination. The assay of pectinesterase
can be accomplished either by the determination of the amount of
methanol liberated (307, 308) or by direct titration of the increase in
carboxyl groups (309). In both cases, pectinic acid serves as a substrate.
b. Occurrence. Pectinesterase has not been reported to occur in the
animal kingdom, but this enzyme is widely distributed in higher plants
and in molds.