MOLECULAR MORPHOLOGY 57 



Aside from the value of comparative studies in suggesting clues 

 about the structure of fibrous proteins, the matter has a biological 

 significance as well. Thus a detailed comparison of the structure and 

 composition of a particular protein, such as keratin, in the various 

 phyla and classes may reveal relationships quite as fundamental as those 

 of comparative anatomy and embryology, 



Astbury and Rudall have begun such a study of the keratins. 

 "Feather" keratin, which is of the beta variety, is found only in reptiles 

 and birds ; in other vertebrates the keratin is of the alpha type. In reptiles 

 the mobile regions of the body are covered with the softer alpha keratin, 

 while the remainder of the body is enclosed in the harder beta variety. 

 Unfortunately the comparative studies on keratin have been made 

 chiefly on the basis of wide-angle x-ray patterns. 



Bear and his associates have been making a careful comparative 

 x-ray study of the collagen type. All vertebrate collagens examined show 

 the same characteristic wide-angle pattern as do also many invertebrate 

 collagens, including those of representative mollusks, annelids, and 

 echinoderms. Recently these investigators have found a similar pattern 

 in gorgonin and spongin, thus furnishing evidence for the existence of 

 this class of proteins in the coelenterates and porifera. The meager data 

 that are available on the amino acid composition of these proteins in 

 the lower forms indicate significant differences from that of vertebrate 

 collagen. Bear's studies of the fiber-axis long spacings have added 

 greatly to the detailed information necessary for comparative studies. 

 It remains to be seen whether, with increasing phylogenetic complexity, 

 this ubiquitous protein type also increases in regularity of molecular 

 architecture or whether, even in the lowest forms, it exists already fully 

 established. The shaft membrane of the trichocysts of Paramecium 

 possesses a structure fully as regular as that of vertebrate collagen, to 

 which it bears some resemblance in chemical properties, as shown by 

 Jakus. 



Will it turn out that the lowest organisms contain protein patterns as 

 complex as those of the higher organisms ; that such complexity of 

 molecular structure is required for life as we know it? If so, what are the 

 missing links between such structural proteins and the simpler organic 

 compounds ? 



Macromolecular Ontogeny 



The general problem of the chemical mechanism of the synthesis of 

 proteins has been considered previously in this symposium. The prob- 



