A Rubber-Like Protein in Insect Cuticle

Abstract

ABSTRACT The cuticle of arthropods is complex and varies enormously in structure, properties and composition even within the same species (cf. Richards, 1951). However, the mechanical behaviour is dominated by materials in the solid state of matter so that the mature cuticles hitherto described in the literature may be classed as solid cuticle. It was therefore surprising to find that certain patches of the exoskeleton in many insects exhibit long-range reversible elasticity of the rubber-like type. This paper describes three examples of rubber-like cuticle from locusts (Orthoptera) and dragonflies (Odonata). Similar structures have been found in all winged insects hitherto examined (Weis-Fogh, unpublished). Essentially the present survey is a qualitative analysis of the material basis for the rubber-like properties of three selected samples, based upon simple tests and techniques. The main conclusion is that the characteristic elasticity is caused by a peculiar protein, called resilin, which differs from other structural proteins also in respect of amino-acid composition (Bailey & Weis-Fogh, 1961). Resilin is insoluble in all solvents which do not break peptide bonds and since it is located as an integral part of the highly organized cuticle it is necessary to analyse the three samples in detail as to structure and many other properties. Only in this way is it permissible to conclude that the elasticity depends on only one type of substance and to characterize it in general terms.