120 



LIGHT AND LIFE 



TABLE 1 

 Some Properties of Pyridine Nucleotide Enzyme Complexes 



Enzyme' 



Free DPNH in 



LDH ADH6 GDH" aGPDH GPD Me. 



Water Carbitol 



' The enzymes are respectively: lactic dehydrogenase of cattle heart (LDH), alco- 

 hol dehydrogenase of horse liver (ADH), glutamic dehydrogenase of cattle liver 

 (CiDH). a-glvcerophosphate dehydrogenase of rabbit skeletal muscle (a-GPDH), and 

 glvceraldehvde-.'5-phosphate dehydrogenase of rabbit skeletal muscle (Gl'D). 



-Grams of protein that comliine with one mole of pyridine nucleotide. 



•' Intrinsic dissociation constants calculated for ccjuivalent and independent com- 

 bining sites. 



' A and B are arbitrary designations of the two reactive positions at pyridine-C-4. 



■• I'olari/ation mcasincd with plane-polarized incident light. 



" l)issociati(m constants for ADM from ref. '5'{. 



'GDH is one of the few en/ymes that works with both DPN and TPN. The 

 dissociation c^)nstaiits for DPNH and Il'N'H are approximately the same, (unpub- 

 lished (iuorometric measurements of Dr. (.arl Irieden). I he value for the oxidized 

 coenzyme was derived kinetically lor I I'N. I hat lor OI'N is also large. 



Polarization. The polarization of DPNH in the LDH complex is 

 near the theoretical niaximtnn ior solution in a rigid mediimi, but 

 in the GPD conijilcx it is only half maximal. This suggests that 

 there are degrees of freedom in the GPD complex that are consistent 

 with the absence of enhancement, but such an explanation is hard 

 to reconcile with the precise orientations that one would expect at 

 a catalytic site. Such behavior may be related to the fact that the 

 coenzyme on (iPI) is in some way involved in the phosphorylative as 



