460 2. ANALOGS OF ENZYME REACTION COMPONENTS 



by heparin is competitive and this was studied in detail by Houck (1957 a), 

 who found competitive behavior from l/v-l/(S) plots for both heparin and 

 chondroitin sulfate B. The inhibitor constants and their variation with 



Ki {mM) 



Temperature K^ (mlf) 



Heparin Chondroitin sulfate B 



6.58 

 6.85 

 7.10 

 7.41 



temperature are tabulated, and from these values it was possible to cal- 

 culate the important thermodynamic quantities shown in the following 

 tabulation: 



- AF<^ - AH° - zl<S° 



(kcal/mole) (kcal/mole) (e. u.) 



Heparin 3.07 5.0 6.8 



Chondroitin sulfate B 3.0 4.9 6.2 



The rather weak binding might indicate that only a fraction of the anionic 

 groups on heparin or chondroitin sulfate B interact at close range with 

 enzyme cation groups. It is difficult to predict the entropy changes in the 

 interactions of such complex molecules because several factors may be in- 

 volved, e.g., the restriction of polymer configuration, possible changes in 

 enzyme structure, and release of water of hj^dration. The rather small 

 changes in AS observed are probably the result of the balancing of larger 

 changes in different directions. The importance of ion-ion interactions is 

 shown by the marked reduction in the inhibitions when the ionic strength 

 rises above 0.3. 



The differences in inhibitory activity between low molecular weight sub- 

 stances and polymers made from them are well illustrated by Hahn and 

 Fekete (1953). Various phenolic compounds inhibit testicular hyaluron- 

 idase weakly, but upon polymerizing these with formaldehyde it is possible 

 to obtain potent inhibitors. Their results are expressed in terms of the po- 

 tency relative to resorcinol. y-Resorcylate has an activity of 1.5 while its 

 polymer has an activity of 980. The most active inhibitor is the polymer 



COO- COO- COO- coo- 



— C— R— C— R— C— R— C— R— C— 



