PROSTHETIC GROUPS, COENZYMES AND ENZYMES 



Cytochrome c has a remarkably low partial specific volume, 



V = 0.702-0.707. After quantitative analysis of all the amino 

 acids we could calculate the V of the protein coinponent; the 

 value found was 0.737. If now the weight of the heme inoiety 

 was added to the protein part under the assumption that it 

 was built into the protein in a way not to increase its volume, 



V would be equal to 0.700. In fact this seeins to be v^ery nearly 

 the case. As seen from Figure \b, the peptide chain left after 

 pepsin digestion occupies one quadrant of the space around the 

 heme disc. If the other quadrants are filled with a-helices in 

 square packing around the cytochrome c heme, this arrangement 

 would explain as well the experimental value for the partial 

 specific volume as the fact that the iron atom is inaccessible to 

 oxygen. Electrons could be led to and from the iron via the 

 free nitrogen atom of the imidazole ring, because this atom, 

 according to our model, would be situated nearer to the surface 

 of the molecule and probably could react with suitable oxidizing 

 or reducing agents, perhaps by chelate formation with heavy 

 metal atoixis of other enzyme systems. 



The recent advances in our knowledge of the cytochrome c 

 structure encourage us to believe that the whole problem can be 

 solved in the not too distant future. A few years ago such a 

 hope would have appeared overly optimistic. 



The Old Yellow Enzyme, a Conjugated Protein with 

 Dissociable but Functionally Immobile Coenzyme 



This enzyme is interesting froin a historical point of view, 

 since it was the first oxidation enzyme that was crystallized; 

 the first that was reversibly split into protein and coenzyme; 

 and the first from which a pure coenzyme was prepared ; and 

 still its physiological function is entirely unknown. 



Warburg and Christian (35), the discoverers of the 

 "O.Y.E.," observed that a yellow dye, which was liberated from a 

 high molecular moiety by treatment with methanol, showed a 

 greenish fluorescence. Kuhn and Moruzzi (7) observed that 



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