Protein complexes, chitin

Chitin is classically a linear polymer of /3-d-(1 - 4)-linked 2-acetamido-2-deoxy-D-glucosyl residues. However, after comparing chitin isolated from different sources, it became evident that substantial variations in solubility, molecular weight, acetyl values, and specific rotation occur among samples. It would appear that chitin is not a single, polymeric entity, but rather, a family of closely related products derived from natural chitin-protein complexes.209... 

Blackwell, J., and Weih, M. A. (1980). Structure of chitin-protein complexes ovipositor of the Ichneumon fly Megarhyssa. Journal of Molecular Biology, 137, 49-60. 

It is important to understand the structure of insect cuticle before we study the cuticu-lar penetration of insecticides. Figure 6.1 shows the structure of insect integument. The integument is the outer layer of the insect, comprising the epidermis and the cuticle. The epicuticle is generally about 1 micron in thickness. It can be composed of as many as four sublayers the cement layer (outermost), the wax layer, the polyphenol layer, and the cuticu-lin layer. The epicuticle, which makes up about 5% of the total thickness of the cuticle, contains lipids, lipoprotein, and protein and, therefore, it is lipophilic. Beneath the epicuticle lies the procuticle, which comprises the exocuticle and the endocuticle. This is essentially a hydrophilic chitin-protein complex containing considerable quantities of water. The endocuticle is soft and is the major constituent of larvae and soft-bodied insects. It is composed of microfibers of chitin and protein, which may impart elasticity to the cuticle. Above this section, the exocuticle is predominant in hard-bodied insects and forms most of the cuticle in adult beetles. It is present only as a thin layer in many larvae and in the hard parts of... 

Figure 5. Proposed arrangement of the protein subunits around the chitin core in Megarhyssa chitin-protein complex. Key a, axial projection and b, projection perpendicular to fiber axis. (Reproduced, with permission, from Ref. 26. Copyright 1980, Academic Press.)...

Rudall, K.M. Conformation of chitin-protein complexes. In Ramachandran, G.N. (ed.) Conformation of Biopolymers. Academic, London (1967)... 

Chitin/Protein complexes are found in fungi and in the arthropod cuticle. Chitin is the poly-N-acetyl-D-glucosamine. 

Rudall, K.M. 1963. The chitin/protein complexes of insect cuticles. Advances in Insect Physiology 1 257-313. 

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