124
P. W. KENT
and chitin as a resistant substance. Analyses of the amino acids (180) in
resilin and other proteins is shown in Tables IV and V. The material
remaining after removal of resilin consists of chitin with about 2% of
protein. Resilin is a structural elastic protein with a three-dimensional
network of peptide chains, in which a new type of cross-linkage participates (178, 180). The mechanical properties of the tissue appear to be
dependent on this type of molecular structure (184, 185). Anderson
(186) has evidence that two new fluorescent amino acids are involved in
the cross linkage; "compound II" brings about the junction of two peptide chains and "compound I" (the less abundant) links three chains.
Since these amino acids absorb at A ma x 320 m/x in alkaline conditions and
resilin is distinguishable from tyrosine-containing proteins (absorbing at
maximally about A300 τημ), it has been possible to show the lineal increase in the concentration of compounds I and II with the amount of
resilin. In the maturation of the adult locust rubberlike cuticle (e.g.,
wing hinge ligament), the total weight increase in chitin and resilin plus
fibrous protein is constant at 5 days after emergence. Only resilin continues to be formed after 1 week in the course of reaching full cuticular
maturity. Though resilin is found in close proximity to chitin, it is not
clear whether the two associate as complementary molecular chains.
B. SKELETAL AND ASSOCIATED MUCOSUBSTANCES
In chitinous structures in different species, a number of proteins are
associated with chitins, and it is of importance to consider to what extent
chitin may be replaced by other types of carbohydrate-containing
polymers.
1. Cellulose
Cellulose was one of the first polysaccharides to be recognized in
invertebrate skeletal tissues (187), under the name of tunicin. This was
detected in Cynthia papiUata, on account of its unusual stability. Subsequently it was found in ascidians and in the larvae of Phallusia mammüaris, where it constitutes the mantle. There is strong evidence that in
the latter, cellulose is synthesized by epidermal, as opposed to mesodermal, cells. In Pyrosoma, the polysaccharide appears to arise from a cytoplasmic process of ectodermal cells penetrating through the integument.
Reports (188) of the presence of cellulose in the tubes of Pogonophora
are not substantiated. In Siboglinum athnticum, S. inermis, and S. caulyeri Brunet and Carlisle (189) showed that although the tubes were
notably stable to alkali and to Schweitzer's solution, acidic or enzymatic
degradation led to glucosamine or to its N-acetyl derivative. Thus the
presence of chitin in these species must be extremely probable. Com-
P. W. KENT
and chitin as a resistant substance. Analyses of the amino acids (180) in
resilin and other proteins is shown in Tables IV and V. The material
remaining after removal of resilin consists of chitin with about 2% of
protein. Resilin is a structural elastic protein with a three-dimensional
network of peptide chains, in which a new type of cross-linkage participates (178, 180). The mechanical properties of the tissue appear to be
dependent on this type of molecular structure (184, 185). Anderson
(186) has evidence that two new fluorescent amino acids are involved in
the cross linkage; "compound II" brings about the junction of two peptide chains and "compound I" (the less abundant) links three chains.
Since these amino acids absorb at A ma x 320 m/x in alkaline conditions and
resilin is distinguishable from tyrosine-containing proteins (absorbing at
maximally about A300 τημ), it has been possible to show the lineal increase in the concentration of compounds I and II with the amount of
resilin. In the maturation of the adult locust rubberlike cuticle (e.g.,
wing hinge ligament), the total weight increase in chitin and resilin plus
fibrous protein is constant at 5 days after emergence. Only resilin continues to be formed after 1 week in the course of reaching full cuticular
maturity. Though resilin is found in close proximity to chitin, it is not
clear whether the two associate as complementary molecular chains.
B. SKELETAL AND ASSOCIATED MUCOSUBSTANCES
In chitinous structures in different species, a number of proteins are
associated with chitins, and it is of importance to consider to what extent
chitin may be replaced by other types of carbohydrate-containing
polymers.
1. Cellulose
Cellulose was one of the first polysaccharides to be recognized in
invertebrate skeletal tissues (187), under the name of tunicin. This was
detected in Cynthia papiUata, on account of its unusual stability. Subsequently it was found in ascidians and in the larvae of Phallusia mammüaris, where it constitutes the mantle. There is strong evidence that in
the latter, cellulose is synthesized by epidermal, as opposed to mesodermal, cells. In Pyrosoma, the polysaccharide appears to arise from a cytoplasmic process of ectodermal cells penetrating through the integument.
Reports (188) of the presence of cellulose in the tubes of Pogonophora
are not substantiated. In Siboglinum athnticum, S. inermis, and S. caulyeri Brunet and Carlisle (189) showed that although the tubes were
notably stable to alkali and to Schweitzer's solution, acidic or enzymatic
degradation led to glucosamine or to its N-acetyl derivative. Thus the
presence of chitin in these species must be extremely probable. Com-