54 BIOCHEMICAL SYSTEMATICS 



_ Activity retained on oxi- 



, . u .'.„" 'ouc^ (Tm iun 'r,N mc jt^^^^ dation by performic acid 



Ser ,n sheep ^lA LYS PHE GLU ARG GN HIS „eT ^ ,o ,he sulfone 



^ ALA ^ A^P 



TIlV^*^" /^ Initial split by subtilisin sER 



A »• > , • A ^^ , ^FP 5^" ^^^ *^* ALA SER THR •• 



Activity retained on guanidination StK 



of amino groups AN 



30 TYR 80 -,, ^-, 



''' "" MET ,, CYS ^„ THR ILEU SER MET THR SER TYR SER ,, 



^.,*«^; ^SE^^^^ ARG ^0 ^^ 



v*"; (LYS 90 ,SERP ^Pepsin inactivates ,*'^ LYS aLA^ 



^^YR \l20 ^™*^^"/^''^ 



^ GLY -/ iVALj 



THR PRO VAL,^^^*^^"'' ''"^ "'^ VAL PRO VAL TYR PRO AN -Ar 



fir X ryj '\'™J 



Glu ^-^ l-YS AN CXPose removes to here A^'i^'^Y '"'t o" reoction 1^^-; 



in sheep ASP ALA without inactivation with bro,.oacetate; activity ,,0 fGLU .J 



^ , . ,wr 'ost on photooxidotion (?) ^ "" 



^"%f TYR LYS THR THR AN ALA GN LYS,, HIS JLEU ILEU VAL ALA \^^^^ 60 

 40 LYS 100 ^ ^— - ^^^^^.^ 



> ALA 



DInitrophenylation / °R0 g^ 



Inactivates ^ VAL „ yy^L 



A"*" THR AIA ASP 



^"'"'< PHE VAL HIS GLU SER LEU ALA 



Fig. 4-2. Amino acid sequence of ribonuclease. Note the effect of 

 specific modifications upon activity. Courtesy C. B. Anfinsen; the 

 figure is a composite of results from the following: C. H. W. Hirs, 

 S. Moore and W. H. Stein, J. Biol. Chem., 235:633 (1960). 

 R. R. Redfield and C. B. Anfinsen, J. Biol. Chem., 385 (1956). 

 D. H. Spackman, W. H. Stein, and S. Moore, J. Biol. Chem., 

 235:648 (1960). J. T. Potts, A. Berger, J. Cooke and C. B. Anfinsen, 

 J. Biol. Chem. (in press). C. Smyth, W. H. Stein and S. Moore, 

 J. Biol. Chem. (in press). 



comparative biochemistry of enzymes at the molecular level. This 

 basis for potential enzyme heterogeneity, the extent of which is illus- 

 trated in Fig. 4-3, has been pointed out by Paul and Fottrell (1961). 

 Mutations that affect the amino acid sequence in nonessential 

 parts of the enzyme can in all likelihood be preserved and will thus 

 represent extremely subtle indices of relationship somewhat analogous 

 to the system of reciprocal translocations of Oenothera chromosomes 

 which have provided valuable insight into the phylogeny of this 

 genus. Progress in comparative enzymology is accelerating now, and 

 such investigations may play an increasingly important role in the 

 study of evolution. Recently, Esser et al (1960) studied twenty-five 

 reverted mutants, presumably back mutations, of the tryptophanless 

 (td2) mutant of Neurospora crassa. Reaction rates for the specific 

 reaction system governed by the gene differed among the reverted 



