The Integument

protein, which in the presence of excess quinone is oxidized to an N-quinonoid protein. The 365

latter is able to react with the terminal amino group or sulfhydryl group of another protein to link the two molecules. In a number of species p-alanine is incorporated into the cuticle during tanning, and it is speculated that this amino acid becomes attached to proteins, leaving its amino terminus free to participate in linking the quinone and protein. In addition, the quinone can react with the £-amino groups of lysine residues in the protein molecule to effect further binding. Autotanning is also a possibility. This is the oxidation of aromatic amino acids (e.g., tyrosine) within a polypeptide chain to form quinone compounds that can subsequently link with amino groups in adjacent chains. Though autotanning has never been demonstrated, "dopa" has been found in small amounts in certain cuticular proteins of Manduca sexta (Okot-Kotber et al., 1994) and presumably could engage in cross-linking reactions.

The color of tanned cuticle depends on the amount of o-quinone that is present. When this molecule is present in small quantities the cuticle is pale; if it is in excess, and especially if it polymerizes, the cuticle when tanned is dark. In some cuticles production of the characteristic dark brown or black color (melanization) is entirely separate from tanning, although it involves tyrosine and its oxidation product dopa. Oxidation of dopa yields dopaquinone which can form an indole ring derivative, dopachrome. Decarboxylation, oxidation, and polymerization then occur to produce the pigment melanin.

As tanning occurs, the cuticle undergoes a number of physical rearrangements. Its water content decreases as a result of (1) a decline in the number of hydrophilic groups such as -NH2 because of their involvement in tanning and (2) a tighter packing of the chitin and protein molecules. This leads to an overall decrease in the thickness of the cuticle.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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