118
P. W. KENT
and the traces of glucosamine detected in the products of chitinase digestion were attributed to free NH 2 groups in the chitin substrate.
Deacetylation of N-acetyl-D-glucosamine reported in bacteria may be
significant in terms of glucosamine turnover.
V. Chitin in Relation to Mucosubstances
A. INTERACTION COMPLEXES
1. Lipid Constituents
The composition of the chitinous exoskeletons of a now wide variety
of biological species indicates that although chitin is widely distributed,
it seldom accounts for more than 70% of the total organic constituents,
and frequently values in the range 25-50% are encountered (80). A
further type of exoskeletal structure can be distinguished in arthropods
of nonchitinous nature, in which the organic components consist principally of sclerotized proteins (157), as in the oothecae of Periplaneta
americana, Blatella germanica, and Orthodera ministralis. In these oothecae, mechanical rigidity is achieved by "tanning," a complex series of
rapid reactions in which proteins are believed to become cross-linked
by a quinone (43). These oothecae have been found (157-159) to contain calcium oxalate (0.2-8%), and it has been suggested (158, 159) that
calcium ions may associate with protein, stabilizing it prior to tanning.
Considerable amounts of calcium as yet unaccounted for are, however,
present in some other form. The existence of protein-calcium complexes
may account for this situation, as in the marine snail Busycon caniculatum, where protein is considered (160) to be linked to carbohydrate
through calcium ions.
In chitinous exoskeletons, lipids and proteins are found in addition
to chitin. Paraffin chains and thermostable bound lipids have been detected by X-rays and electron diffraction in epicuticle of a number of
insects: Periplaneta americana (161), Tenebrio molitor (162), and Calliphora erythrocephah
(163). In Tenebrio, the lipid molecules are
oriented to the cuticular surface. The existence of a lipid surface layer
appears to play a significant biological role in maintaining the water
balance of these animals. The lipid deposition is a late stage in the
formation of epicuticle, and lipid is reported (164, 165) to be transported by means of some solubilizing agent (161) from the epidermal
cells, forming a discontinuous layer on a tanned protein matrix. There
is, however, little information (166, 167) on the chemical nature of the
lipids concerned; some evidence points to the presence of an eight-
P. W. KENT
and the traces of glucosamine detected in the products of chitinase digestion were attributed to free NH 2 groups in the chitin substrate.
Deacetylation of N-acetyl-D-glucosamine reported in bacteria may be
significant in terms of glucosamine turnover.
V. Chitin in Relation to Mucosubstances
A. INTERACTION COMPLEXES
1. Lipid Constituents
The composition of the chitinous exoskeletons of a now wide variety
of biological species indicates that although chitin is widely distributed,
it seldom accounts for more than 70% of the total organic constituents,
and frequently values in the range 25-50% are encountered (80). A
further type of exoskeletal structure can be distinguished in arthropods
of nonchitinous nature, in which the organic components consist principally of sclerotized proteins (157), as in the oothecae of Periplaneta
americana, Blatella germanica, and Orthodera ministralis. In these oothecae, mechanical rigidity is achieved by "tanning," a complex series of
rapid reactions in which proteins are believed to become cross-linked
by a quinone (43). These oothecae have been found (157-159) to contain calcium oxalate (0.2-8%), and it has been suggested (158, 159) that
calcium ions may associate with protein, stabilizing it prior to tanning.
Considerable amounts of calcium as yet unaccounted for are, however,
present in some other form. The existence of protein-calcium complexes
may account for this situation, as in the marine snail Busycon caniculatum, where protein is considered (160) to be linked to carbohydrate
through calcium ions.
In chitinous exoskeletons, lipids and proteins are found in addition
to chitin. Paraffin chains and thermostable bound lipids have been detected by X-rays and electron diffraction in epicuticle of a number of
insects: Periplaneta americana (161), Tenebrio molitor (162), and Calliphora erythrocephah
(163). In Tenebrio, the lipid molecules are
oriented to the cuticular surface. The existence of a lipid surface layer
appears to play a significant biological role in maintaining the water
balance of these animals. The lipid deposition is a late stage in the
formation of epicuticle, and lipid is reported (164, 165) to be transported by means of some solubilizing agent (161) from the epidermal
cells, forming a discontinuous layer on a tanned protein matrix. There
is, however, little information (166, 167) on the chemical nature of the
lipids concerned; some evidence points to the presence of an eight-