C;. WEBER 



99 



is essentially that of tryptophan and its simple derivatives, but with 

 some interesting general differences, as well as characteristic differences 

 among the proteins themselves. 



In general, while the ratio of the polarizations observed upon 

 excitation with 305 ni/^ and 270 rufx light (P30.-./P270) has a value of 

 1.4-1.7 in tryjito])han and the simple indole derivatives, the correspond- 

 ing ratios in the proteins in cold propylene-glycol — water ranges from 

 2.2-3 and from 1.8-2.5 in water at room temperature. 



The peak observed in N-glycyl tryptophan at 295 ni/x is present in 

 more than half of the globular proteins examined. The differences 

 observed among the different globular proteins relate to (a) the 

 ratio p30ii/p2-o> which is variable from one protein to the next; 

 (b) the presence and magnitude of the small band at 295 m^, very 

 noticeable in lysozyme, small in the albumins, and virtually absent in 

 ovalbumin; and (c) the fall in polarization in the region of wave- 

 lengths longer than 310 m/A (Figs. 13-16) . In most cases a pro- 

 nounced fall is observed, which is however less well marked in other 

 albumins than in ovalbumin, where a flat peak at 310 m/x is ob- 

 served. It is of significance that most of these details in the polariza- 



Polarization Spectra of Ovalbumin 



0-I6- 

 OI5 



014- 



OI3 

 QI2 



on 

 p 

 010 



009 

 008 

 007 

 006 

 005 

 004 

 003 

 002 

 001 



•—• in Phosphate Buffer pH70 

 o — o Isoelectric Ovalbumin 

 o- o in 8M Urea 



220 230 240 250 260 270\280 290 300 3IO 320 

 Fig. 13. Polarization spectra of ovalbumin under various conditions. 



tion spectrum are lost when the proteins are dissolved in urea. The 

 details become nuich less conspicuous and the ratio p.3o.-)/p27o reaches 

 the values 1.3-1.6. Removal of the urea results in the case of some 

 proteins in an almost complete restoration of the original spectrum 

 (e.g., human and serum albumins) , whereas in others, such as rabbit 



