416
PETER BERNFELD
tion, ranging from two to six, are formed. Then, another enzyme hydrolyzes the di- and oligosaccharides to the monomer. This mechanism
has been found to prevail during the biological breakdown of amylose
by α-amylases and maltases, of cellulose by cellulase and cellobiase, as
well as in some less-known systems, as in the degradation of chitin by
chitinase to chitobiose. An exception to the two-stage mechanism is the
degradation of amylose by glucamylase from fungi, and it is believed
that the one-stage mechanism of degradation may be preferred by some
lower organisms.
In some instances, it has been suggested that the depolymerization of
insoluble polysaccharides is carried out in a three-stage reaction. Such
a mechanism is similar to the two-stage reaction discussed above, with
the exception that the random depolymerization of the soluble polysaccharide is preceded by another stage during which the insoluble high
molecular substrate is transferred into a soluble, but still high molecular,
compound. The mechanism of such a reaction is probably identical with
that of the depolymerization which follows, and it may be a matter of
further research to decide whether the enzymes acting on the insoluble
substrate are actually different from the ones that depolymerize the
soluble polysaccharide. An example of the three-stage mechanism is the
system of the Ci and C x cellulases, the former being capable of solubilizing cellulose to some extent, the latter being the actual cellulase
which acts upon the high molecular, but more or less soluble, substrate. Another example is the protopectinase-depolymerase-polygalacturonase system.
A rather unique enzyme within the group of polysaccharidases is
β-amylase. Its mechanism of action is entirely different from the type
involving random splitting which has been discussed above and which
appears to be rather general. ß-Amylase is also peculiar in its almost
exclusive occurrence in higher plants, but its role in nature is not well
understood.
Polysaccharidases may include the first enzymes ever discovered and
studied by men, but much is still to be learned about them.
References
1. K. Meyer, in "Polysaccharides in Biology," Transactions of 1st Conference,
(G. F. Springer, ed.), p. 31. Corlies, Macy, New York, 1956.
2. G. S. C. Kirchhoff, Mem. Acad. Imp. Sei. St. Petersburg 4, 27 (1811).
3. E. F. Leuch's, Poggendorff's Ann. physik. Chem. 22, 623 (1831).
4. A. Payen and J. Persoz, Ann. chim. et phys. 53, 73 (1833).
5. Bouchardat and Sandras, Compt. rend. acad. set. 20, 143 (1845).
6. M. W. Beijerinck, Centr. Bakteriol. Parasitenk. Abt. II, 1, 221 (1895).
7. S. Peat, G. J. Thomas, and W. J. Whelan, /. Chem. Soc. p. 722 (1952).
PETER BERNFELD
tion, ranging from two to six, are formed. Then, another enzyme hydrolyzes the di- and oligosaccharides to the monomer. This mechanism
has been found to prevail during the biological breakdown of amylose
by α-amylases and maltases, of cellulose by cellulase and cellobiase, as
well as in some less-known systems, as in the degradation of chitin by
chitinase to chitobiose. An exception to the two-stage mechanism is the
degradation of amylose by glucamylase from fungi, and it is believed
that the one-stage mechanism of degradation may be preferred by some
lower organisms.
In some instances, it has been suggested that the depolymerization of
insoluble polysaccharides is carried out in a three-stage reaction. Such
a mechanism is similar to the two-stage reaction discussed above, with
the exception that the random depolymerization of the soluble polysaccharide is preceded by another stage during which the insoluble high
molecular substrate is transferred into a soluble, but still high molecular,
compound. The mechanism of such a reaction is probably identical with
that of the depolymerization which follows, and it may be a matter of
further research to decide whether the enzymes acting on the insoluble
substrate are actually different from the ones that depolymerize the
soluble polysaccharide. An example of the three-stage mechanism is the
system of the Ci and C x cellulases, the former being capable of solubilizing cellulose to some extent, the latter being the actual cellulase
which acts upon the high molecular, but more or less soluble, substrate. Another example is the protopectinase-depolymerase-polygalacturonase system.
A rather unique enzyme within the group of polysaccharidases is
β-amylase. Its mechanism of action is entirely different from the type
involving random splitting which has been discussed above and which
appears to be rather general. ß-Amylase is also peculiar in its almost
exclusive occurrence in higher plants, but its role in nature is not well
understood.
Polysaccharidases may include the first enzymes ever discovered and
studied by men, but much is still to be learned about them.
References
1. K. Meyer, in "Polysaccharides in Biology," Transactions of 1st Conference,
(G. F. Springer, ed.), p. 31. Corlies, Macy, New York, 1956.
2. G. S. C. Kirchhoff, Mem. Acad. Imp. Sei. St. Petersburg 4, 27 (1811).
3. E. F. Leuch's, Poggendorff's Ann. physik. Chem. 22, 623 (1831).
4. A. Payen and J. Persoz, Ann. chim. et phys. 53, 73 (1833).
5. Bouchardat and Sandras, Compt. rend. acad. set. 20, 143 (1845).
6. M. W. Beijerinck, Centr. Bakteriol. Parasitenk. Abt. II, 1, 221 (1895).
7. S. Peat, G. J. Thomas, and W. J. Whelan, /. Chem. Soc. p. 722 (1952).