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Essays in Biochemistry- 



Table 1. Amino Acid Composition of Rihonuclease 



(The values for the stable amino acids are the average of six determinations) 



Residues per Mole 



* Extrapolated values for amino acids that show decomposition on hydrolysis. 



t The average of triplicate determination of cystine as cysteic acid. 



X Average of two determinations of amide NH3. 



§ Amide groups not included in the summation of the total number of residues. 



data in Table 1, Anfinsen et al. proposed the structure for ribonuclease 

 shown in Fig. 1.* The existence of four disulfide bridges in the molecule 

 was assumed wdien attempts to detect sulfhydryl groups failed. 

 Ledoux 10 has claimed, on the basis of experiments with oxidizing and 

 reducing agents such as H 2 2 , HCN, and reduced glutathione, that 

 sulfhydryl groups are essential for enzymatic activity. Davis and 

 Allen 2n and Dickman and Aroskar,- 1 on the other hand, could find no 

 evidence for the presence of sulfhydryl groups in the molecule. This 



* At the time this structure was proposed, it was not appreciated that there 

 are probably five and not four proline residues in the molecule. 



