STRUCTURAL BASIS OF RIBONUCLEASE ACTIVITY 



133 



^ip/j.= 0.08? 



\/aI. 5«r.AU-' Soj- 



Fig. 4. Schematic representation of tlie effect of 8 M urea and performic acid on 

 ribonuclease. 



figure is by no means the final story. In general, however, bonding between 

 half-cystines located near the beginning and end of the chain is indicated. 



In Fig. 4 w^e have also introduced, for conversational purposes, three tyrosine 

 carboxyl interactions as suggested by the studies of Shugar and others. Upon 

 treatment of the native molecule with 8 INI urea, the structure of the molecule 

 may become extensively disoriented, much more, perhaps, in a relative way 

 than shown here, since the partial unfolding of the helical coiling which un- 

 doubtedly exists in certain spatially restricted areas of the molecule may add 

 considerable to this disorientation. Upon oxidation of the native molecule a 

 somewhat greater, but not necessarily much greater, disorientation can take 

 place. 



In view of the dramatic changes in structure which appear to occur in strong 

 urea solutions, tests were made on ribonuclease for enzyme activity in which 

 the activity measurements were carried out in 8 M urea. To our considerable 

 surprise the molecule appeared to be as active and perhaps more active, than 

 the native molecule under these circumstances (Anfinsen et al, 1955). 



Fig. 5 shows a first order reaction plot of data taken from experiments in 



