BENT LEY GLASS 835 



Studies of artificial conjugates have been limited mainly to con- 

 jugates of proteins with dimcthylamino na|)hlhalene sidfochloride 

 (DNS) . These studies have been of use in determining the rotational 

 relaxation times, the dielectric properties of the medium and its 

 variation with conditions, and the "molecidar expansions." Con- 

 jugates of DNS with bovine serum albimiin show, by the fluorescence 

 excitation spectra of the DNS emission, a transfer of electron energy 

 from tryjjtophan residues to the attached DNS. After 20 hours of 

 tligestion with chymotrypsin, the transfer disappears, because, in the 

 resulting peptides, the tryptophan residues and the DNS have be- 

 come separated. Analogously, expansion of a protein by penetration 

 of methyl-ethyl carbinol at 3° C produces a cessation of energy trans- 

 fer. This may be analyzed quantitatively by comparing the fluores- 

 cence of the native protein with that of the DNS conjugate. The 

 characteristic distance for the transfer of electron energy from trypto- 

 phan to DNS was found by Weber to be 24 A; and the effective 

 average distance from a tryptophan residue to the DNS group was 

 19.5 A in Waaler, 23.3 A in 30 7f methyl-ethyl carbinol, and 25.8 A in 

 9.5 M urea. If we assimie an isotropic expansion of the molecular 

 volume, its increase is 50 per cent in methyl-ethyl carbinol and 90 

 per cent in urea. 



Sidney F. Velick used the concept of excited states, as known from 

 absorption and emission spectra, to illuminate the nature of the re- 

 lationship between protein and coenzyme in the enzyme complexes 

 now known to be essential to enzymic activity. True, a coenzyme may 

 alternatively be regarded either as a substrate or as a prosthetic group 

 of the enzyme, depending upon the dissociability of the complex. But 

 whichever is the case, it is the relations of the coenzyme in the com- 

 plex to both the protein and other substrates that "determine speci- 

 ficity and reaction mechanism and that are the focal points for meta- 

 bolic integration and control." 



The pyridine and flavin nucleotides, having been most intensely 

 studied in these respects, afford special insight into the nature of 

 these enzyme complexes. Reduced diphosphopyridine nucleotide 



(DPNH) exists in the form of two isomers, a and f3 the former 

 biologically inactive, the latter the active form. N. O. Kaplan and 

 his coworkers, who discovered the inactive isomer, have done much 

 to elucidate the reasons for its inactivity. The a isomer differs ster- 



ically from the (3 isomer at the nicotinamide riboside bond. When 



