Protein Structure and Information Content 



115 



weight of 120, A/,/residue is given in Table I for those proteins in Fig. 4 for 

 which the molecular weights are available. 



Thus A/, for the loss in specific activity is of the order of 0.25 bits/residue 

 (the 0.68 value for egg albumin does not correspond to a loss in specific activity). 

 This indicates that destruction of the right 5 to 25 per cent of /, (assuming 

 /p is close to our minimum estimate of I to 4 bits/residue) causes loss of function, 

 which may be reversible or irreversible depending upon which intramolecular 

 bonds are disrupted. 



PEPSIN 



T= 298° K 



T= 323° K 



PROTEINASE 



TRYPSIN (KINASE) 



TRYPSIN 



INVERTASE 



INVERTASE 



VIBRIOLYSIN 



TETANOLYSIN 



HEMOLYSIN (GOAT) 



RENNIN 



T = 328°K 



LEUCOSIN 



INVERTASE (YEAST 

 I NVERTASE 



T=333 



EMULSIN (WET) 

 AMYLASE (MALT) 

 SOLAN IN 

 HEMOGLOBIN 



TOSS" K 

 EGG ALBUMIN 



T=343°K 

 PEROXIDASE (MILK) 



T= 353° K 

 INSULIN 



Fig. 4. The equivalence between AS* and A/^ for thermal inactivation. The 



shaded areas to the left represent AF* and the clear areas to the right AS*. 



(Adapted from Fig. 1, ref 12, by courtesy of University of Illinois Press.) 



Summary 



The above discussions indicate that redundancy considerations are not 

 the explanation of the large excess of structural information content; rather, 

 that only a small fraction of the potential information on the surface of the 

 molecule is actively utilized in information transfer. Haurowitz (18), for 

 instance, has pointed out that experiments with substituted antigens indicate 

 that the antigenic specificity resides in an area on the surface of the protein 

 which is approximately 10 to 15 A in diameter. Results cited here suggest 



