ENZYME COMPLEXES 



be studied only within the context of the over-all process. If 

 we wish to isolate any single reaction and study it separately 

 this is possible only if we have available ( 7) a mechanism for the 

 generation of the substrate (s), (2) a method for introducing the 

 substrate (s) into the over-all pathway, and (3) a means of 

 blocking off subsequent changes by the use of inhibitors. Analy- 

 sis of individual enzymes within the array with respect to their 

 characteristic chemical composition or to their prosthetic groups 

 or cofactors is possible only if such an assignment can be made 

 in an unambiguous manner on the basis of supplementary 

 evidence. If we know for instance that (7) all flavoproteins 

 absorb at 450 m^, (2) the value of the molecular extinction 

 coefficient for flavoproteins in general at this wavelength, and 

 (3) that under certain conditions a certain definite measurable 

 change at 450 m/i can be due only to the reduction of a particular 

 flavoprotein, then we cannot only assay for this flavoprotein 

 within the cell but also follow the kinetics of its reduction and 

 reoxidation. 



If I am to be allowed a horribly anthropomorphic analogy, 

 we may look at our problem as similar to one which asks us to 

 account for the location and movements of a large number of 

 individuals within a building. Evidently from the very outset 

 these positions and movements will be restricted by the nature 

 of the building and by its internal architecture, the size and 

 location of the rooms, the position of stairways, elevator shafts, 

 etc. By placing a large number of telescopes and mirrors external 

 to the building, we may hope to keep all the inhibitants under 

 constant observation and plot their movements as lines on a 

 plan of the building. Nevertheless there will always be spots 

 within the structure which are hidden from our view, notably 

 in doorways, stairs, and elevators, especially when relatively 

 large numbers of the inhibitants are in motion simultaneously, 

 even if this motion be perfectly orderly and according to some 

 prearranged plan. But even more fundamxcntally our problem 

 cannot possibly become completely determinate without an 

 appreciation of the various individuals involved and a careful 

 analysis of their individual properties. 



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