58 RADIATION BIOLOGY 



peptide bonds linked by hydrogen bonds as in I: 



(1-47) 



An effective electron transfer from one end of the chain to the other 

 occurs when the tautomer II is produced by the migration of all linking 

 protons in the chain from the equilibrium bonding position near nitrogen 

 to that near oxygen. In this way an electron delivered at some terminal 

 group attached to the chain could result in an electron being made avail- 

 able at the other end of the chain near the heme group of cytochrome C. 

 This general idea has been indicated in the work of several authors, 

 including Huggins (1943), Denbigh (1944), Wirtz (1947), and Schmidt 

 (1947). These authors have, in addition, suggested the possibility that 

 forms I and II are companion resonance structures of a conjugated sys- 

 tem, there being a possibility in this way that an oxidized or reduced 

 form of the protein could be produced with low activation energy. Stabi- 

 lization of ionic forms of protein molecules through the existence of many 

 resonance structures could thus perhaps explain the catalytic activities 

 of enzymic proteins. However, Evans and Gergely (1949) showed that 

 the overlap of electronic orbitals across hydrogen bonds is insufficient to 

 allow resonance. Geissman has favored a resonance-like oscillation of 

 hydrogen atoms across the interpeptide linkages, but this phenomenon 

 would, of course, produce negligible resonance stabilization and is very 

 unlikely to occur. 



The lack of precise chemical information about proteins has led to a 

 rash of special theories to explain the very high efficiencies of enzymes in 

 catalysis. Among the most reasonable of these is that which may be 

 compounded from the work of Michaelis (1946), Kalckar (1946), and 

 LuValle and Goddard (1948). The mechanism applies to oxidative 



