ENZYME COMPLEXES 



regard the protein as a semiconductor or as a macro resonating 

 system involving the hydrogen bonds of the polypeptide chain, 

 have been proposed by others and have been critically reviewed 

 recently (6,21). 



Semiquantitative calculations have actually been carried 

 out by Evans and Gergely (12) and have led to the assignment 

 of at least partially metallic character to some of the valence 

 electrons associated with the polypeptide structure. The 

 present suggestion would certainly imply further increase in the 

 conductive nature of the protein or provide a possible alternate 

 explanation of such conductive phenomena. Once again as in 

 the metalloflavoprotein case the introduction of a metal atom, 

 or as here of a large number of metal atoms, should lead to a 

 much larger variety and a smearing-out of possible energy 

 states in the complex molecule and to an enhancement of the 

 possibilities and rates of interaction with external donor and 

 acceptor systems (see also ref. 21, pages 32-40). 



The speculative picture which I should like to advance, in 

 order to focus attention on a possible new parameter to this 

 problem, is based on some observations on the composition of 

 DPNH oxidase (24,25) and on some aspects of the present-day 

 thinking concerning metallic conduction (18). The enzyme 

 contains a large number of non-heme iron and copper ions 

 (15 of the former per flavin and approximately 4 per cytochrome 

 b hemin; 2 to 3 of the latter per cytochrome oxidase hemin) 

 tightly bound to the protein. It is possible that electron 

 transport from flavin to cytochrome c or from one cytochrome 

 to the next is mediated at least in part by a conducting core of 

 metal ions linked to and surrounded by the polypeptide helix 

 (34). The latter would then function in some measure like an 

 insulating sheath. The metal ions may form a complex with one 

 or more of the nitrogen and one or more of the oxygen atoms of 

 the helix by actual bond formation but some of the orbitals of 

 the metal will remain unfilled and free to interact with similar 

 unfilled orbitals of neighboring metal atoms. This property 

 then might impart a metal-like character to the chain of metal 



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