INHIBITION OF ENZYMES 

 Table 1-6 (continued) 



31 



" The activities were determined in several different ways: in some the dehydro- 

 genase was measured directly with a dye, in others the oxygen uptake from succinate 

 in either crude preparations or mitochondria, with or without added electron trans- 

 porters. Since the dehydrogenase has been shoAvn to be the sensitive portion of the 

 total oxidase, it is likely that the results refer to inhibition of the dehydrogenase only. 



^ lodoacetamide used rather than iodoacetate. 



rather small change in inhibition as the iodoacetate is increased; this may 

 well be a reflection of the sluggishness of the reactions. From inspection of 

 the table, succinate dehydrogenase from all forms of life seems to be of 

 approximately equal sensitivity to iodoacetate, although mammalian en- 

 zymes may be somewhat more easily inhibited. 



There is very little work on the mechanism of the inhibition or on the 

 enzyme groups reacted. When inhibition proceeds so slowly, one must be 

 more concerned with reaction of groups other than SH. Barron and Singer 

 (1945) provided evidence than non-SH groups may be involved in pigeon 

 muscle succinate dehydrogenase. The enzyme was allowed to react with 

 p-chloromercuribenzoate to complete inhibition; some of this enzyme was 

 then incubated with either iodoacetate or iodoacetamide for 35 min. Reac- 

 tivation with glutathione gave 84% recovery of the enzyme treated with 

 only the mercurial, 68% recovery when treated with mercurial and iodo- 

 acetamide, and 13% recovery when treated with mercurial and iodoacetate. 

 If the mercurial is assumed to react with SH groups only, they reasoned 

 that iodoacetate must react with something else. However, there are several 



