STRUCTURE -FUNCTION RELATIONSHIPS IN PROTEINS AND 

 THEIR POSSIBLE BEARING ON THE PHOTOSYNTHETIC PROCESS 



Rvifus Lumry 



Structure -function relationships in muscle have been studied for many 

 years. Aside from these, however, such relationships of biological systenns 

 at the single molecule level have aroused little interest until the last few 

 years. What little work there is to date is largely confined to single proteins 

 and has attempted to explain the unusual characteristics of the unique physio- 

 logical reactions of these proteins in ternas of conformational factors. A 

 good example is the attempt in the field of vision to show that light produces 

 a conformation change in rhodopsin which converts it from a noncatalytic to a 

 catalytic protein, thus to produce by chemical amplification a sufficient ,^. 



change in chennical composition near an end plate to initiate neurone function. 

 In organized systems such as the mitochondrian there has been the unexplained 

 but highly dramatic occurrence of a swelling and shrinking associated with the 

 integrity of Ihe oxidative phosphorylation system and the rate of phosphoryla- 

 tion itself. ^ ' ' In addition, there has been some evidence that physical 

 properties such as strength of adherence of sub-proteins in the mitochondrian 

 depend on specific binding of r^eagents known to influence in a marked degree 

 the phosphorylation arocess. ^ ' According to a recent report of Weinbach, 

 Shefield and Garbus^'^ the swelling of mitochondria disappears on removal of ftie 

 uncoupling reagent. This removal is effected by adding serum albumenwhich 

 has a higher affinity for the uncoupling agent. ATP must also be added to the 

 suspension. The swelling and shrinking reaction is complex, but seems to 

 involve the muscle -like action of contractile proteins in the mitochondrial 

 membranes. Somewhat similar changes in morphology occur as the steady- 

 state rate of phosphorylation is altered in normal mitochondria. The impli- 

 cations of such findings appear to be that the effects are due to specific chenn- 

 ical interactions and not to minor modifications in osmotic balance; and that 

 there is sonne connection between the morphological state of the mitochondrian 

 and the chemical state of sonne of its fixed reactants. The characteristic 

 times observed for changes in morphology would appear to be considerably 

 slower than the characteristic tinnes of the chemical processes so that 



swelling and shrinking seem to depend on the steady-state concentration of one 

 or more reactants. It is not yet necessary to suppose that a reversible cycle 

 of morphological changes accompanies any single chemical reaction in phos- 

 phorylation. 



A nunnber of years ago Lucille Smith observed an interesting dependence 

 of the light scattering of suspensions of Rhodospiril lu rn rubrum fragments 

 on light intensity and concomittant rate of reaction. This result suggests 



that the granum may also manifest swelling and shrinking processes related 

 to its chennical or photochemical processes. In the last two years Packer Tias 

 observed that the chloroplasts of higher plants nnanifest the sanne kind of light 

 scattering behavior and he has shown that light scattering and photophosphor - 

 ylation are closely related. More detailed studies of the nnorphological 



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