STUDIES ON THE MOLECULAR 



ORGANIZATION OF 



INSECT CUTICLE^ 



By a. GLENN RICHARDS and RUDOLPH L. PIPA 



Department of Entomology and Economic Zoology, 

 University of Minnesota 



(With Two Plates) 



Specialists in the field have long recognized that the common idea 

 of insect cuticle being composed basically of chitin is an inadequate 

 description. It is probably incorrect too. As far back as the middle 

 of the nineteenth century Berthelot suggested that cuticle was really 

 a chitin-protein combination rather than a mixture. Various twentieth- 

 century biologists and chemists have suggested that cuticle is a natural 

 mucopolysaccharide or glycoprotein (see Richards, 1951). The gen- 

 eral tendency among research workers in this field today is to think 

 of cuticle as a glycoprotein that becomes modified and stabilized by 

 sclerotization but which before sclerotization is relatively unstable. 

 But there is no unambiguous proof that cuticle is a glycoprotein, and 

 students of sclerotization usually ignore the chitin moiety. 



In honor of Dr. R. E. Snodgrass, one of the great insect anatomists, 

 we submit this little study of molecular anatomy of the cuticle. In 

 this paper we will consider four related questions: (i) Are the 

 protein molecules (arthropodin) sufficiently elongated to exhibit form 

 birefringence? (2) What are the optically anisotropic units in nor- 

 mal cuticle, i.e., is cuticle optically simply a chitin-protein mixture 

 or is there a chitin-protein optical unit? (3) Can the orientation of 

 arthropodin molecules be deduced from optical analyses? (4) What 

 are the relative orientations of chitin and arthropodin chains in 

 insect cuticle? 



MATERIALS AND METHODS 



For pieces of cuticle with a high degree of orientation of micelles 

 or crystallites, we used tendons (apophyses) from the legs of cock- 

 roaches (Periplaneta and Blaberus) and tarantulas. After gently 



1 Paper No. 3183, Scientific Journal Series, Minnesota Agricultural Experi- 

 ment Station, St. Paul i, Minn. 



Acknowledgment is made for assistance in this work provided by a grant 

 from the National Science Foundation. 



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