200 FREDERICK G. E. PAUTARD 



In spite of the regularity with which the cross-/? pattern appears in 

 the photographs of solvent-treated flagella, it is uncertain whether 

 this can be called the "natural" state, since the flagellar protein ap- 

 pears to be very unstable and can be changed into the /^-configuration 

 by heating at comparatively low temperatures. This is shown, for ex- 

 ample, in the diffraction photograph in Fig. 4e, where a sharp continu- 

 ous ring at 4.65 A develops when films of flagella are heated to 50°C 

 for 5 min. This configurational instability is further illustrated in films 

 of flagella treated or extracted with acid. Even at concentrations of 1 % 

 acetic acid, dried films, stretched and unstretched, of both acidified 

 flagella and acid extracts show very pronounced cross-/? diffraction 

 diagrams (Fig. 4/). This feature of transformation with acid into the 

 cross-/? configuration has been observed also in whole muscles and 

 actomyosin (Pautard, 1959). 



INFRARED ABSORPTION SPECTRA 



Although the infrared absorption spectrum of proteins gives in- 

 formation of a less detailed kind than that which can be obtained by 

 x-rays, it has a certain quantitative advantage in exploring also the 

 noncrystalline state. In the k-m-e-f proteins (but not exclusively so) 

 there are two absorption peaks of peculiar importance. The first, at 

 1625 cm -1 , is characteristic of the ^-configuration, whether the chains 

 are extended, as in /?-keratin, feather keratin, and silk fibroin, or trans- 

 versely folded, as in the egg stalk of the lacewing fly, Chrysopa (Parker 

 and Rudall, 1957). A second broad peak at 1655 cm -1 can best be 

 classified as "configurations other than /?" since it does not discriminate 

 between the a-configuration and intermediately folded or coiled states. 

 Astbury (1958) has commented on the relation between the x-ray dif- 

 fraction diagram and the infrared absorption spectrum of native and 

 heat-denatured egg albumin. In the muscle proteins, pure myosin 

 shows little or no change in the spectrum after acidification or heating 

 (for example, 100°C for 1 min), whereas actin appears to be trans- 

 formed under such conditions into the Estate (Graham, Parker, and 

 Pautard, in preparation), suggesting that the changes in the spectrum 

 of actomyosin are associated with the globular rather than the fibrous 

 component. 



The phenomenon of the "acid shifts" in the infrared absorption 

 spectrum was in fact first observed in fish sperm flagella. Acetic acid 



