574 G. SCHMIDT 



Observations of Anfinsen et al}^-^^ suggest that ribonuclease I contains 

 only one C terminal group (valine) and one N terminal group (lysine). 

 The analysis of ribonuclease I by means of X-ray diffraction suggests the 

 presence of five crystallographic chains per molecule.^® Elliott" studied 

 the infrared spectrum of single crystals of ribonuclease I and observed 

 dichroism indicating the presence of folded polypeptide chains. According 

 to Anfinsen, the available information suggests the working hypothesis 

 that ribonuclease I consists of a single peptide chain which is folded to the 

 five crystallographic chains postulated on the basis of the X-ray diffraction 

 patterns of ribonuclease I crystals. ^^ Possibly the four cystine groups" '^^-ei 

 present in each molecule of ribonuclease are involved in maintaining the 

 folded structure of the protein (Fig. 7). According to Anfinsen,^^ ^^g g^- 



[NHJ 



LYS-GLU-THR-ALA 



r 



[PRO] 



S ^ 



i [PRO] 



r 



[PRO] 



[PRO] 



■ [MET,TYR,ALA,LEU,PHE]- VAL 



Fig. 7. Scheme of the shape of the molecule of ribonuclease I. [From Anfinsen ei 

 al.^^\ (The abbreviations are symbols for amino acids.) 



zymic activity of ribonuclease I is destroyed by digestion with crystallized 

 pepsin. During the first phase of this digestion approximately 65% of the 

 activity is lost without a measurable appearance of new end-groups and 

 without a significant decrease of the sedimentation rate.^^ This slow phase 



'^ C. B. Anfinsen, M. Flavin, and J. Farnsworth, Biochim. et Biophys. Acta 9, 468 



(1952). 

 " C. B. Anfinsen, R. R. Redfield, W. L. Choate, J. Page, and W. R. Carroll, /. Biol. 



Chem. 207, 201 (1954). 

 " H. Carlisle and H. Scouloudi, Proc. Roy. Soc. (London) A207, 496 (1951). 

 "A. Elliott, Proc. Roy. Soc. (London) A211, 490 (1952). 

 68 E. Brand, Ann. N. Y. Acad. Sci. 47, 187 (1946). 

 6' G. R. Tristram, Advances in Protein Chem. 5, 145 (1949). 

 *" J. H. Northrop, M. Kunitz, and R. M. Herriott, "Crystalline Enzymes," p. 26, 



New York, 1948. 

 *' "Symposium on Mechanism of Enzyme Action" (W. D. McElroy and B. Glass, 



eds.). Johns Hopkins Press, Baltimore, 1953. 

 «2C. B. Anfinsen, /. Biol. Chem. 196, 201 (1952). 

 83 D. Shugar, Biochem. J. 52, 142 (1952). 



