Studies in the chemistry of the insect cuticle

Abstract

Protein, carbohydrate and a sulfur-containing component are present in the cuticles of a variety of insects. The protein fractions are usually large and show similar general properties, The protein of the larval cuticle of Sarcophaga falculata was characterized by the determination of its N distribution, tyrosine, tryptophan, glycerine and [beta]-hydroxy-[alpha]-amino-acid values. S and conjugated non-protein components were absent. The protein was distinct from collagen in its chem. comp.; it resembles sericin, but does not have the high serine content of the latter. Similar proteins from the hawk moth larva (Sphinx ligustri) and the lobster were characterized in the same way. Certain marked differences from the blowfly protein were recorded in each case. The tyrosine value of 11.7% of the wt. in the hawk moth protein is remarkably high. The protein of the hard, melanized puparium of Sarcophaga differed from the larval protein mainly in a loss of solubility and the replacement of part of its tyrosine by melanoid oxidation products. These latter were reduced, extracted and shown to have some of the properties of hallachrome. The possible formation of chitin from a homogeneous fluid polysaccharide-protein complex secreted by the hypodermis is briefly discussed.