8. POLYSACCHARIDASES
403
oryzae, A. niger). Hydrolysis of xylan by this group of enzymes appears
to be slow and incomplete. The insolubility of the substrate appears to
be a limiting factor during xylan degradation, and this behavior is
analogous to that encountered during enzymatic degradation of cellulose
and of retrograded amylose.
IX. Enzymes That Hydrolyze Polyuronides
A. PECTIC ENZYMES
This group of enzymes has recently been reviewed by Kertesz (294).
According to the complexity of their substrates, there are at least three
distinct enzymes participating in the biological breakdown of pectic
substances.
1. The Substrate (295)
a. Protopectin. The parent substance, protopectin, is insoluble in
water, and its chemical nature is not yet completely understood. Protopectin is closely associated with cellulose in the matrix of the cell walls.
Restricted hydrolysis of insoluble protopectin yields pectins or pectinic
acids.
b. Pectinic Acids and Their Salts. Pectinic acids and pectinates are
polygalacturonic acids in which from 20 to 90% of the carboxyl groups
are present as methyl ester and which are capable of producing colloidal
solutions in water.
c. Pectins. Pectins are chemically not different from the pectinic
acids. They are capable, however, of forming jellies with sugar and
acid under suitable and well-specified conditions.
d. Pectic acids and Their Salts. Pectic acids and pectates are polygalacturonic acids that are essentially free from methyl ester groups
and capable of yielding colloidal solutions with water.
2. Nomenclature of Pectic Enzymes
According to the chemical reactions involved, there are at least two
possible enzymes participating in the biological degradation of pectic
substances. The first is an enzyme that causes the fissure of glycosidic
linkages and, hence, reduces the molecular weight of the substrate.
The second is an esterase which is capable of splitting the methyl ester
groups. Various terms have been used for the enzymes fulfilling these
two functions, and it has been postulated that more than one enzyme
that splits the glycosidic bonds exists. Table XXII summarizes the functions and terminology of pectic enzymes.
The various terms for the active principle that catalyzes the hy-
403
oryzae, A. niger). Hydrolysis of xylan by this group of enzymes appears
to be slow and incomplete. The insolubility of the substrate appears to
be a limiting factor during xylan degradation, and this behavior is
analogous to that encountered during enzymatic degradation of cellulose
and of retrograded amylose.
IX. Enzymes That Hydrolyze Polyuronides
A. PECTIC ENZYMES
This group of enzymes has recently been reviewed by Kertesz (294).
According to the complexity of their substrates, there are at least three
distinct enzymes participating in the biological breakdown of pectic
substances.
1. The Substrate (295)
a. Protopectin. The parent substance, protopectin, is insoluble in
water, and its chemical nature is not yet completely understood. Protopectin is closely associated with cellulose in the matrix of the cell walls.
Restricted hydrolysis of insoluble protopectin yields pectins or pectinic
acids.
b. Pectinic Acids and Their Salts. Pectinic acids and pectinates are
polygalacturonic acids in which from 20 to 90% of the carboxyl groups
are present as methyl ester and which are capable of producing colloidal
solutions in water.
c. Pectins. Pectins are chemically not different from the pectinic
acids. They are capable, however, of forming jellies with sugar and
acid under suitable and well-specified conditions.
d. Pectic acids and Their Salts. Pectic acids and pectates are polygalacturonic acids that are essentially free from methyl ester groups
and capable of yielding colloidal solutions with water.
2. Nomenclature of Pectic Enzymes
According to the chemical reactions involved, there are at least two
possible enzymes participating in the biological degradation of pectic
substances. The first is an enzyme that causes the fissure of glycosidic
linkages and, hence, reduces the molecular weight of the substrate.
The second is an esterase which is capable of splitting the methyl ester
groups. Various terms have been used for the enzymes fulfilling these
two functions, and it has been postulated that more than one enzyme
that splits the glycosidic bonds exists. Table XXII summarizes the functions and terminology of pectic enzymes.
The various terms for the active principle that catalyzes the hy-