BIOMOLECULAR ASPECTS OF SPERMATOZOAN MOTILITY 197 



X-RAY DIFFRACTION 



X-ray diffraction studies of biological subjects can often provide 

 most fundamental indications of their nature. The muscle proteins, 

 for example, are a remarkable illustration of Astbury's x-ray classifica- 

 tion of the configurations of the fibrous proteins (see for example Ast- 

 bury, 1947a). Muscle gives a wide-angle pattern typical of the a-con- 

 figuration common to all proteins of the k-m-e-f (keratin-myosin-epi- 

 dermin-fibrinogen) group. There is, besides, a number of meridional 

 reflections identifiable with actin (Astbury et al., 1947), a globular 

 protein with apparently close molecular-biological affinity to feather 

 keratin (Astbury, 1947b). This combination of two proteins repre- 

 sents a "pair-in-hand" arrangement that might be common through- 

 out nature, with one or the other partner predominating in a particu- 

 lar tissue, some tissues, however, such as porcupine quill and reptile 

 keratin, suggesting intermediate states. In this scheme of things, mus- 

 cle is simply part of a much wider plan, but it does show, perhaps more 

 clearly than any other tissue, how closely the two molecular species are 

 coupled together in the k-m-e-f group of proteins. In the bacterial 

 flagella, x-ray diffraction studies (Astbury et al., 1955) have shown that 

 even here, too, in this simplest of contractile organelles, the same plan 

 is present and the same combination of actin-like and myosin-like 

 molecular species occurs. Moreover, the diffraction pattern of bacte- 

 rial flagella shows an added arc on the meridian at 4.65 A, the cross-/? 

 reflection (Rudall, 1946) being attributed to the folding of polypep- 

 tide chains transverse to the fiber axis. This configuration is closely 

 associated with the supercontracted state (see, for example, Astbury 

 et al., 1959, for details and history) that can be induced in all the 

 k-m-e-f proteins, and the property of shortening from the folded <*- 

 form to the collapsed cross-/? form has been proposed by Astbury as 

 the ultimate molecular basis of muscular contraction (e.g., Astbury, 

 1947a). 



In the flagella based on the 9 plus 2 system there is no report of simi- 

 larities in detail with the x-ray diffraction patterns from muscle and 

 bacterial flagella. Salmon sperm tails, separated by ultrasonic methods, 

 give a diffuse protein pattern (Lowman and Jenson, 1952), while the 

 diffraction pattern of algal flagella reported by Astbury and Saha 

 (1953) is now seen to arise from an artifact (Astbury and Pautard, 



