CHAPTER 2
Chitin and Mucosubstances
P. W. KENT
Department of Biochemistry, University of Oxford, Oxford, England
I. Introduction
93
II. Distribution of Chitin
94
A. In Microorganisms
94
B. In Plants
96
C. In Animals
97
III. Molecular Structure and Function of Chitin
100
A. Physical Structure and Properties
100
B. Chemical Structure of Chitin
108
IV. Biochemistry of Chitin
112
A. Enzymatic Degradation
112
B. Biosynthetic Pathways
116
V. Chitin in Relation to Mucosubstances
118
A. Interaction Complexes
118
B. Skeletal and Associated Mucosubstances
124
References
.
130
I. Introduction
In 1799, Hachett (I) decalcified shells of crabs, lobsters, prawns, and
crayfish with mineral acids, observing that they "produced a moderate
effervescence and in a short time were found to be soft and plastic of a
yellowish color and like a cartilage, which retained the original figure."
Although this is the first mention of calcified chitin in invertebrates, its
recognition is usually ascribed to Odier (2) in 1823, who obtained a
hornlike material after treatment of cockchafer elytra with potassium
hydroxide and proposed the name chitin. The nitrogenous nature of
chitin was revealed by the experiments of Children (3) in 1825. Until
quite recently these methods for isolating "pure" chitin by decalcification
with acids and deproteinization with alkalis have continued virtually
unchanged. It is now evident that chitin, considered exclusively as a
polysaccharide, is not normally found, and in situ it is associated with
other substances, notably proteins, by hydrogen bonds and covalent
linkages. A convenient method of distinction proposed by Hackman (4)
reserves the name chitin for the chemically purified material and native
chitin for the complex in which it is involved in tissues.
93
Chitin and Mucosubstances
P. W. KENT
Department of Biochemistry, University of Oxford, Oxford, England
I. Introduction
93
II. Distribution of Chitin
94
A. In Microorganisms
94
B. In Plants
96
C. In Animals
97
III. Molecular Structure and Function of Chitin
100
A. Physical Structure and Properties
100
B. Chemical Structure of Chitin
108
IV. Biochemistry of Chitin
112
A. Enzymatic Degradation
112
B. Biosynthetic Pathways
116
V. Chitin in Relation to Mucosubstances
118
A. Interaction Complexes
118
B. Skeletal and Associated Mucosubstances
124
References
.
130
I. Introduction
In 1799, Hachett (I) decalcified shells of crabs, lobsters, prawns, and
crayfish with mineral acids, observing that they "produced a moderate
effervescence and in a short time were found to be soft and plastic of a
yellowish color and like a cartilage, which retained the original figure."
Although this is the first mention of calcified chitin in invertebrates, its
recognition is usually ascribed to Odier (2) in 1823, who obtained a
hornlike material after treatment of cockchafer elytra with potassium
hydroxide and proposed the name chitin. The nitrogenous nature of
chitin was revealed by the experiments of Children (3) in 1825. Until
quite recently these methods for isolating "pure" chitin by decalcification
with acids and deproteinization with alkalis have continued virtually
unchanged. It is now evident that chitin, considered exclusively as a
polysaccharide, is not normally found, and in situ it is associated with
other substances, notably proteins, by hydrogen bonds and covalent
linkages. A convenient method of distinction proposed by Hackman (4)
reserves the name chitin for the chemically purified material and native
chitin for the complex in which it is involved in tissues.
93