We investigated the physical and chemical properties of highly extensible elastic fibres from the octopus aorta. These fibres are composed of an insoluble rubber-like protein which we call the octopus arterial elastomer. The amino acid composition of this protein is different from that of other known protein rubbers, being relatively low in glycine and high in acidic and basic residues. Up to extensions of 50%, mechanical data from native elastic fibres fit a theoretical curve for an ideal Gaussian rubber with elastic modulus G = 4.65 × 105 N m−2, and this is unchanged by prolonged exposure to formic acid. Thermoelastic tests on this protein indicate that the elastic force arises primarily from changes in conformational entropy, as predicted by the kinetic theory of rubber elasticity. Analysis of the non-Gaussian behaviour of the elastic fibres at extensions greater than 50% suggests that the molecular chains in this octopus protein are somewhat less flexible than those in resilin or elastin. Some speculations on the molecular design of these protein rubbers are made.

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