409
that the egg capsule surrounding near-term Mustelus canis shark embryos was permeable to substances smaller than 5 kDa in size. Therefore it is not surprising that
this transverse channels system with structural similarity to liquid crystalline
construction have large biomimetic potential (Knight et al. 1996 ).
Collagen is also located within other structures observed on the surface of egg
capsules, the tendrils. The tendrils of the egg capsule of the dogfi sh S. canicula
appear to act as damped spring which becomes entangled with one another, attaching the capsule fi rmly to the seaweed Halidrys siliquosa . The tendrils have a unique
structure (see for details Feng and Knight 1994a ). Intriguingly, tendrils and capsule
wall both appear to be constructed from similar components: transversely banded
collagen fi brils and amorphous granules. Both are constructed from lamellae built
up from laminae. However, the tendril has a spiral concentric construction apparently derived from rotation of the tendril within the tendril forming region; whereas
the lamellae of the egg capsule form as a simple laminated extrusion. The tendril
exhibits a marked primary twisting and secondary coiling; while the egg capsule of
the dogfi sh is only slightly twisted. In the tendril, the fi brils are arranged at approximately right angles to one another in adjacent laminae. This is in contrast to the
orthogonal arrangement with an angle of approximately 45° between fi brils in adjacent laminae in the capsule wall (Knight and Hunt 1976 ; Gathercole et al. 1993 ).
12.2 Polyphenol-Containing Egg Capsule Proteins
Formation of skate egg capsules begins in the nidamental gland with the secretion
and assembly of capsular precursors (see for detail Koob and Cox 1988 ). These
materials are white when assembled. They gradually develop color with time in
utero, eventually producing the deep greenish brown characteristic of skate capsules at oviposition. In Raja erinacea , the tanning of capsules in utero is coincident with the introduction of catechols into the capsular matrix (Koob and Cox
1986 ). An enzymic activity able to oxidize catechols to quinones has been demonstrated histochemically in tanning capsules and nidamental glands from several
oviparous elasmobranchs.
Brown ( 1955 ) reported that sections of newly formed Raja egg capsules turned
brown upon incubation with tyrosine, and that this reaction could be blocked by
potassium cyanide. She believed that these results demonstrated a polyphenol oxidase which would oxidize the polyphenol present in the capsule to quinone which,
in turn, would tan the capsule (Koob and Cox 1988 ). A polyphenoloxidase was
demonstrated histochemically in the shell glands of S. canicula by incubating sections of fi xed glands with catechol (Threadgold 1957 ). Krishnan ( 1959 ) showed that
both capsular material and sections of frozen glands from Chiloscyiium griseum
oxidized catechol, and that the capsule had chemical properties like other quinone
tanned matrices. He suggested that capsule formation involved a form of quinone
autotanning catalyzed by a phenoloxidase (Koob and Cox 1988 ). Since works by
Koob and Cox ( 1988 ) and Cox and Koob ( 1993 ), it was established that catechol
oxidase plays a pivotal role during the formation of skate egg capsules by catalyzing
12.2 Polyphenol-Containing Egg Capsule Proteins
that the egg capsule surrounding near-term Mustelus canis shark embryos was permeable to substances smaller than 5 kDa in size. Therefore it is not surprising that
this transverse channels system with structural similarity to liquid crystalline
construction have large biomimetic potential (Knight et al. 1996 ).
Collagen is also located within other structures observed on the surface of egg
capsules, the tendrils. The tendrils of the egg capsule of the dogfi sh S. canicula
appear to act as damped spring which becomes entangled with one another, attaching the capsule fi rmly to the seaweed Halidrys siliquosa . The tendrils have a unique
structure (see for details Feng and Knight 1994a ). Intriguingly, tendrils and capsule
wall both appear to be constructed from similar components: transversely banded
collagen fi brils and amorphous granules. Both are constructed from lamellae built
up from laminae. However, the tendril has a spiral concentric construction apparently derived from rotation of the tendril within the tendril forming region; whereas
the lamellae of the egg capsule form as a simple laminated extrusion. The tendril
exhibits a marked primary twisting and secondary coiling; while the egg capsule of
the dogfi sh is only slightly twisted. In the tendril, the fi brils are arranged at approximately right angles to one another in adjacent laminae. This is in contrast to the
orthogonal arrangement with an angle of approximately 45° between fi brils in adjacent laminae in the capsule wall (Knight and Hunt 1976 ; Gathercole et al. 1993 ).
12.2 Polyphenol-Containing Egg Capsule Proteins
Formation of skate egg capsules begins in the nidamental gland with the secretion
and assembly of capsular precursors (see for detail Koob and Cox 1988 ). These
materials are white when assembled. They gradually develop color with time in
utero, eventually producing the deep greenish brown characteristic of skate capsules at oviposition. In Raja erinacea , the tanning of capsules in utero is coincident with the introduction of catechols into the capsular matrix (Koob and Cox
1986 ). An enzymic activity able to oxidize catechols to quinones has been demonstrated histochemically in tanning capsules and nidamental glands from several
oviparous elasmobranchs.
Brown ( 1955 ) reported that sections of newly formed Raja egg capsules turned
brown upon incubation with tyrosine, and that this reaction could be blocked by
potassium cyanide. She believed that these results demonstrated a polyphenol oxidase which would oxidize the polyphenol present in the capsule to quinone which,
in turn, would tan the capsule (Koob and Cox 1988 ). A polyphenoloxidase was
demonstrated histochemically in the shell glands of S. canicula by incubating sections of fi xed glands with catechol (Threadgold 1957 ). Krishnan ( 1959 ) showed that
both capsular material and sections of frozen glands from Chiloscyiium griseum
oxidized catechol, and that the capsule had chemical properties like other quinone
tanned matrices. He suggested that capsule formation involved a form of quinone
autotanning catalyzed by a phenoloxidase (Koob and Cox 1988 ). Since works by
Koob and Cox ( 1988 ) and Cox and Koob ( 1993 ), it was established that catechol
oxidase plays a pivotal role during the formation of skate egg capsules by catalyzing
12.2 Polyphenol-Containing Egg Capsule Proteins