HUGO THEORELL 



dation around 50 at />H 7, 5 at pH 8. Since in the liver the alde- 

 hyde is rapidly removed by an aldehyde oxidase, alcohol oxida- 

 tion can proceed smoothly. 



In the case of yeast ADH the Z)^^ and D^^^ are not very 

 different, and accordingly there is practically no "protein con- 

 centration effect" on the equilibrium or the redox potential. 



This is an illustration of how enzymes adapt coenzymes 

 for quite different functions. Yeast produces alcohol from 

 acetaldehyde, whereas liver ADH catalyzes the opposite re- 

 action. We might say that the same alcohol that is produced 

 by aldehyde oxidizing DPNH in the yeast is oxidized by DPN 

 back to aldehyde in the liver. For these opposite purposes 

 Nature has been able to use the same DPN-DPNH system, by 

 producing proteins with different properties. 



Theorell and Chance derived some useful formulas for the 

 system 



DPNH -f ADH' , *' - DPNH. ADH' (1) 



DPNH ADH' + GHsCHO + H+ , *' ^ DPN ADH' + GzHbOH 



(2) 



DPN ADH' , *' - DPN -}- ADH' (3) 



kt 



The initial reaction velocity (at f'^O), in terms of reacted sub- 

 strate and coenzyme molecules per 1 ADH' -molecule per time 

 unit ("turnover number"), was under these assumptions cal- 

 culated to be 



i X ^ = -. , \ r-^-^ (4) 



e at 



kix [H+]/(:4a \ kix) kz 



An analogous formula can be derived for the reverse reaction 

 (Jkh instead of h; k^ instead of [H+]A;4; k2 instead of ks] and a then = 



[G2H6OH], X = [DPN]) (4a) 

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