Cuticle composition

As a result of these large compositional differences, these two layers of the cuticle can be expected to react differently to permanent waves, bleaches, and even water and surfactants. Raper et al. [72] have described a method to determine the cuticle composition from endocuticle of chemically treated wools. Such a procedure would be valuable to evaluate changes in the endocuticle of cosmetically modified human hair. 

The cuticle surface membrane contains a lipid and a proteinaceous component the term epicuticle is sometimes used to describe this surface membrane (Figure 5.5). However, it must be remembered that the epicuticle was originally defined as the membrane raised from the fiber surface. It is highly resistant and is raised as bubbles or saes from the underlying material after treatment with chlorine and water [50]. After isolation by agitation, as mentioned above, the epicuticle was shown to be predominantly proteinaceous [51]. Its similarity to cuticle composition led King and Bradbury to suggest that the isolated membrane consisted of multilayers derived from the fiber surface [49]. These authors also found lipids to be associated with the epicuticle. 

To further understand and manipulate the fiinctional and structural properties of natural resilin, Qin et al expressed the three exons of the Drosophila CG15920 gene, which encodes the full-length native resilin sequence, including the chitin-binding domain. This recombinant resilin exhibits comparable structural and mechanical behaviors to those previously reported, and the introduction of chitin-binding domain provides additional opportunities for formation of the resilin-chitin cuticle composite structure. 

Wool fibers have a very complex morphological stmcture. They can be considered as biological composite materials, in which the various regions are both chemically and physically different (87). Fine wool fibers contain two types of cell those of the internal cortex and those of the external cuticle. 

Ohnishi, E. 1959. Pigment composition in the pupal cuticles of two colour types of the swallowtails, Papilio xuthus L. and P. pmtenor demetrius Cramer. J. Insect Physiol., 3 132-145. 

Mosle B, Collinson M, Finch P, Stankiewicz A, Scott A, Wilson R (1999) Factors influencing the preservation of plant cuticles a comparison of morphology and chemical composition of modem and fossil examples. Org Geochem 29 1369-1380... 

Terrestrial BMOs have also been widely used for monitoring environmental contaminants. In particular, the lipid-like waxy cuticle layer of various types of plant leaves has been used to monitor residues of HOCs in the atmosphere. However, some of the problems associated with aquatic BMOs apply to terrestrial BMOs as well. For example, Bohme et al. (1999) found that the concentrations of HOCs with log KoaS < 9 (i.e., those compounds that should have attained equilibrium) varied by as much as 37-fold in plant species, after normalization of residue concentrations to levels in ryegrass (Lolium spp.). These authors suggested that differences in cuticular wax composition (quality) were responsible for this deviation from equilibrium partition theory. Other characteristics of plant leaves may affect the amount of kinetically-limited and particle-bound HOCs sampled by plant leaves but to a lesser extent (i.e., <4-fold), these include age, surface area, topography of the surface, and leaf orientation. 

As can be seen from the examples discussed so far, pheromones present on spider cuticle or silk frequently play an important role in spider communication, but limited information is available about their composition. Lipids, whose primary function is regulation of water content, also may have important roles in communication. 

The composition of lipids from the silk and cuticule has been reviewed by Schulz (1997a, 1999). These lipids consist primarily of alkanes, as found in other arthropods, with 2-methylalkanes with an even number of carbon atoms in the chain being most abundant, with lesser amounts of alcohols, acids, aldehydes, and wax esters. Recently, a thorough analysis of the silk lipids of N. clavipes (Schulz, 2001) revealed a unique class of lipids from spider silk and cuticle, consisting of straight-chain and branched methyl ethers (1-methoxyalkanes, Fig. 4.4) with chain lengths between 25 and 45 carbon atoms. 

The avian egg shell is covered by a tegmentum or true cuticle which is morphologically constructed of two layers. The cuticle of freshly layed eggs (chicken) exhibits a reddish fluorescence which is due to porphyrins373. The chemical composition of the cuticle has been described to contain proteoglycans with a relatively... 

Wedral, E., Vadehra, D. V., Baker, R. C. Chemical composition of the cuticle, and the inner and outer shell membranes from eggs of Callusgallus. Comp. Biochem. Physiol. 47B, 631 (1974)... 

Hackman, R. H., and Goldberg, M. (1987). Comparative study of some expanding arthropod cuticles the relation between composition, structure and function. Journal of Insect Physiology, 33, 39-50. 

Lockey, K.H. (1988). Lipids of the insect cuticle origin, composition and function. 

We know the most about cuticular hydrocarbons, because they are abundant and because it is relatively easy to isolate and identify them. They are also the most hydrophobic lipid components, and so should provide the best barrier to water-loss. -Alkanes isolated from insect cuticles typically have chain lengths of 20-40 carbons. These can be modified by insertion of cis double bonds, or addition of one or more methyl groups. Relatively polar surface lipids include alcohols, aldehydes, ketones and wax esters (see Chapter 9). Given this diversity, is it possible to predict lipid phase behavior (and, by extension, waterproofing characteristics) from composition alone If so, a large body of literature would become instantly interpretable in the context of water balance. Unfortunately, this is not the case. 

Transpiration through the cuticle involves more than just the single step of diffusion through the epicuticular lipid layer. Molecules of water must leave the tissues adjacent to the cuticle, diffuse through the cuticle itself, enter the lipid layer, diffuse across the lipids, and enter the gas phase outside the animal. Each step is likely to be affected by temperature to a different extent. Lipid composition and physical properties can also differ from one region of the cuticle to the next, so that the biophysical details of cuticular transpiration may not be homogeneous across the entire animal. Thus, transpiration at the organismal level involves multiple steps, and parallel routes for water flux. 

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