The cuticle of the cockroachPeriplaneta americana- V. The chemical resistance of the impregnating material of the cuticle, and the 'self-tanning' of its protein component

Abstract

The developing cuticle ofPeriplanetashows some resistance to chemical attack even before the onset of the phenolic tanning which gives it its final hardness and colour. This early resistance is due to the impregnation of the cuticle with a lipoprotein complex. Histological and histochemical examination suggest that the combination of the sterol and protein moieties of the complex is dependent on the occurrence of some degree of aromatic bonding of the protein even before final tanning takes place. During this initial or primary aromatic bonding no marked colour is developed, and the active agent is not derived from a dihydroxyphenol, as it is in final tanning, but is a quinone formed by the oxidation insituof the tyrosine component of the protein moiety. No free dihydroxyphenol is involved, and the protein may be referred to as ‘self-tanning’. During the process of final hardening the protein of the impregnating complex undergoes further tanning. There is some evidence that the sterol also may be involved in this process, not merely through its association with the protein, but directly owing to its combination with the tanning agent.