631 



Rufus Lumry 



the P700 pigment as a distorted form of chlorophyll. Some support for this 

 idea comes from the studies of Izawa, Itho, Ogawa and Shibata' ' who fovind 

 that treatment of isolated chromatophores of Rhodospir ilium rubrum by the 

 strong protein denaturing agent, dodecylbenzene sulfonate, shifted the 878nnji 

 peak of bacteriachlorophyll to 778 m|j.. They attributed the effect either to the 

 removal of a pre-existing interaction with proteins or with carotenoids, but it 

 is probable that in either case the very large effect is dependent on protein de- 

 naturation. Frenkel has observed reversible shifts of the 878 m|ji peak to 

 shorter wavelengths in dilute detergent solutions.^ ' 



It has been shown that cytochrome c derives its iron electronic properties, 

 notably the oxidation-reduction potential, in part from distortions of ligands 

 enforced by the protein. Judging from the hennoglobin mechanism these prop- 

 erties may be further modified through strong interactions with neighboring 

 proteins. This leads to the idea that the quantitative behavior of chloroplast 

 enzymes as well as cytochromes and other pigmented proteins can be modified 

 by structural factors to be different from behavior found in studies of the iso- 

 lated proteins. There are, of course, possibilities for dielectric effects 

 particularly a local reduction in effective dielectric constant as a result of high 

 lipoid content though the ease of permeation of chloroplast fragments by char- 

 ged molecules suggests that these effects are not very important. At present 

 there seems to be no evidence that the c-type cytochromes of the photosynthe- 

 tic system have unusual oxidation-reduction potentials. However, it is al- 

 most certain in view of the tightness of interaction among constituents that 

 some fixed reactants derive the precise values of their electronic properties 

 from distortion produced in forming the granum. 



The most extreme suggestion provided by the work on heme -proteins is that 

 of dynamic interaction of proteins in the granum or mitochondrian. As a result 

 of strong aggregation conformational changes in one protein may be spread to 

 nearby proteins to produce alterations in the chennical properties of these pro- 

 teins. Changes in the chennical state of one protein could produce changes in 

 its structure which are spread to nearby proteins. If the structure of the 

 granum is sufficiently strong, whole chains of protein-supported single-step 

 reactions could be coordinated in this way. Such a mechanisnn might, for 

 example, coordinate the interaction between the two light acts to explain the 

 puzzling observation that the quantum yield of photosynthesis is nearly inde- 

 pendent of light color for wavelengths shorter than about 685 m|j.. 



An additional example in point is the mechanism of the collection of snnall 

 packets of negative free energy to form a single packet of significant size to 

 cause a needed chemical reaction. Muscle is a system designed to convert 

 chemical energy into mechanical energy. Because of the principle of detailed 

 balancing,at least in theory, it can be made to work backward to convert mech- 

 anical energy into chemical energy. It is believed that two one-electron pro- 

 cesses are required in the mitochondrian to produce enough negative free 

 energy for each molecule of ATP formed. One way to collect the required 

 energy is to first convert the chemical energy of the two one-electron steps 

 into mechanical energy of the phosphorylating enzyme. The latter then acts 

 like muscle working backward to reconvert this energy in a single process 

 into chemical energy of phosphorylation. This proposal is less unreasonable 

 than it sounds since the free energies for phosphorylation are small and could 

 easily be acconnmodated by nninor distortion of proteins without any miajor re- 

 folding processes. On the other hand the single -packet energies involved in 

 the production of oxygen in photosynthesis are relatively large and there must 

 be considerable question as to the possibility that the large stock-piling of 



