290 CELL HEREDITY 



TABLE 10.3 



Comparison of Amino Acid Sequence of Cytochrome c Peptide to 



which Heme Attaches 



Italicized amino acids arc those which differ from species to species; 



.... indicates end of the peptide. 

 (After Vaughan and Steinberg, 1959, Adv. in Prot. (.'/urn., 14:140.) 



Horse ...Vol. Glu{N) . Lys .Cys. Ala. Glu(N) . Cys . His . Thr . Val . Ghi . Lys . . . . 



Reef 



IT .... Lvs . Cvs . Ala . Glu( N ) . Cvs . His . Thr . Val . Gin . Lvs . . . . 



Pig 



Salmon ...Val. Glu(N). Lvs. Cys. Ala . Glu(N) . Cvs. His . Thr . Val . Glu . . . . 



Chicken .... Val . Glu(N) . Lys . Cys . Ser . Glu(N ) . Cvs . His . Thr . Val . Glu ... . 



Silkworm ....Val. Glu(N). Arg. Cys. Ala . Glu(N). Cys. His . Thr . Val . Glu . . . . 



Yeast .... Phe . Lys . Thr . Arg . Cys . Glu . Leu . Cys . His . Thr . Val . Glu .... 



disulphide bridges. There mav, however, be regions of the polypeptide 

 chain in which the particular amino acids present are not of critical im- 

 portance either for activity or for configuration, and these may be the 

 ones which vary from species to species. 



Another line of investigation concerns what is known as the "active 

 site of the enzyme. What chemical and structural alterations can occur 

 without loss of enzymatic activity? Intensive investigations of a few 

 enzymes have revealed the rather unexpected finding that considerable 

 tampering with structure is possible in some instances without loss of 

 activity. An extreme example is papain, which can be degraded by the 

 action of the enzyme leucine aminopeptidase down to less than half of 

 its original size without loss of activity. On the other hand, the slight- 

 est degradation of the peptide hormone glucagon leads to inactivation. 

 In general, enzymes have been found to contain some regions which are 

 much more sensitive than others to any structural change. Thus en- 

 zvmes have "active sites or catalytic regions to which the substrate is 

 bound, and which are highlv substrate-specific in their configuration. 

 Other regions of the molecule may be less directly implicated in enzyme 

 function, and structural alterations there mav have less drastic effects 

 upon function. For example, the enzyme /3-galactosidase is not inacti- 

 vated at all by combining with its specific antibody, although the com- 

 bination with antibody is completely inacti\ating for most enzymes. 

 Presumably the active site of /3-galactosidase is exposed and available 

 to substrate in the enzyme-antibody complex. 



A beautiful example of the essentialitv of some amino acids and not 

 of others at a functionally important site is afforded by studies of cyto- 

 chrome c from different species. The peptide to w hich the heme pros- 



