INHIBITION OF ENZYMES 



37 



Table 1-7 

 Inhibition of Creatine Kinase by Iodoacetate 



(page 205). All investigators, despite variation in results, agree that this 

 enzyme in the isolated state is inhibited by very low concentrations of 

 iodoacetate and is usually as sensitive as 3-PGDH, with the exception of 

 Cori et al. (1958). The poor inhibitions observed by the latter workers may 

 possibly be attributed to their incubation of the enzyme and inhibitor at 

 1° for only 20 min, or to their dialysis of the inhibitor from the enzyme 

 before assaying the activity, or it may be that rat muscle creatine kinase 

 is less reactive than the enzymes from other sources. We may also note 

 that Geiger (1956) reported the creatine kinase from chicken gizzard to be 

 rapidly inactivated by iodoacetate, although no data were given. The cor- 

 responding arginine kinase from crayfish muscle may not be as sensitive, 

 inasmuch as Morrison et al. (1957) found only 19% inhibition at 1 raM 

 iodoacetate and 92% at 10 mM iodoacetate. Treatment of muscle with 

 iodoacetate followed by extraction and examination of 3-PGDH and crea- 

 tine kinase showed that the former enzyme could be inhibited completely 

 without affecting the kinase at all, which is probably explained by the pro- 

 tection provided by a variety of substances (creatine-P, ATP, ADP, etc.) 

 (Padieu and Mommaerts, 1960). Carlson and Siger (1959) also found the 

 creatine kinase to be less readily inhibited in muscle, and that treatment of 

 muscle with 0.5 raM iodoacetate for 30 min at 20° blocks glycolysis without 

 significantly affecting the kinase. One must thus conclude that despite the 



