104 



LIGHT AND LIFE 



residues in the protein conjugate. I have determined R experimentally 

 by a method similar to that employed in the study ol transfer from 

 phenol to indole (28), using lO/j. layers of concentrated solutions of 

 indole and DNS-NHo in a viscous medium. R is found to be 24 A, 



ACTION OF SEC. BUTANOL ON FLUORESCENCE 

 EXCITATION SPECTRA OF DNS CONJUGATES 

 OF BCVINE SERUM ALBUMIN 



400i- 



-. water 



— • sec.Bulanol at3°C. 

 sec. Butanol at 38°C. 



240 280 320 360 400 



Wavelength of excitation 



lig. IH. Ilii()ics(ciuc cxcilation spcdra of l)()viiic scrum alhiimiii toiijiigalctl with 

 DNS. ill melhyl-ctliyl carbinol at two tcinpcratiircs, and in walci. 



while the value calculated from Forster's theory is 26 A, 



The following table gives the values of r found for conjugates of 

 bovine serum albumin, having 1.-^ DNS conjugated groups per mole- 

 cule, and the effect of the addition of 9.5 M urea and of 30% v/v 

 of methyl-ethyl carbinol upon f. 



The last column gives the effective increase in the molecular volume 

 on the assumption that isotropic expansion is responsible for the ob- 

 served increase in f. 



The examples quoted should suffice to give an idea of the type and 

 range of application to which observations on the emission charac- 

 teristics of native proteins and artificial conjugates can lend themselves. 



