64 BIOLOGICAL CHEMISTRY 



TABLE X. 

 Products of Dissociation of H Z C0 3 . 



C H PH or log [H 1 ] C H2 co 3 C H co 3 C co 3 



10 s 5 0.9704 0-0296 



10 6 6 0-768 0-232 



io7 7 0-248 0-752 



io~ 9 9 0-005 0.955 o-oi 



io 11 II 0-003 0-437 0-56 



10 12 12 0-002 0-075 0-p2J 



From the above table we see that if the active portion were 

 the undissociated acid the greatest activity would be in acid 

 solution (C H = io~ 5 or more) ; if the active portion were the 

 first dissociation product, corresponding to HCO;, the greatest 

 activity could be slightly on the alkaline side of the neutral 

 point (C H = io~ 9 ) and if the active portion were the second 

 dissociation product, corresponding to COr, the greatest 

 activity would be in alkaline solution (C H = io~ 12 or less). 



If the action of trypsin depended upon the first dissociation 

 product, corresponding to the HCO;T ion, we see that the 

 activity of trypsin would increase, as the alkalinity increases, 

 up to a certain alkalinity and then decrease as the second 

 dissociation, corresponding to the formation of the COa~ ion, 

 becomes more important.* 



Invertase acts like an amphoteric electrolyte with an acid 

 dissociation constant of io~ 6 ' 7 and a basic dissociation con- 

 stant of about io~ 12 . The hydrolysis of sugar is said to be due 

 to the undissociated invertase hence the optimum activity 

 corresponds to the isoelectric point (or zone in this case). 

 The negative ion is inactive ; the positive ion is also inactive 

 and is in addition easily destroyed.! 



Other enzymes have been studied in a similar way and 

 deductions have been made as to the nature of the active 

 portion. It is interesting to have some method of explaining 

 the influence of hydrogen ion concentration on enzyme 

 activity and also on enzyme destruction. 



INFLUENCE OF THE CONCENTRATION OF THE ENZYME 



We commenced this chapter by stating that the enzyme 

 may be said to alter the constant k in the velocity equation. 

 We have already seen that the rate of enzyme action is 

 affected by the temperature and acidity of the medium in 



* S. P. L. S0rensen, loc. cit. p. 463. It is possible that the decrease 

 in activity might be due to a decrease in ionisation owing to the excess 

 of base decreasing the ionisation of the salt (see p. 36). 



f S. P. L. S0rensen, loc. cit. p. 460. 



