ENZYME REACTIONS AT SURFACES 35 



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DISCUSSION 



A. M. Chase, A. D. McLaren, L. Lorand, A. Marshak, W. D. McElroy, K. Faigen 



Dr. Chase: The enhanced activity of invertase at the surface of plant cells where the 

 local hydrogen ion concentration was actually greater than in the bulk medium reminds 

 me of an old observation by Bertrand and Rosenblatt in volume 158 of the Comptes 

 rcndiis. They reported that yeast suspension lost all invertase activity when heated for 

 I minute at 80°, but regained it if the temperature was raised to 90° or 100°. I have 

 repeated their experiment and got the same result. Could this phenomenon be explained 

 in terms of some localized effect? 



Dr. McL.\ren: Undoubtedly, but I have no idea how. 



Dr. Lorand: I should Hke to raise two questions briefly: ii) In your discussion you 

 seem to have tacitly assumed that liie same active center (identical in its details) func- 

 tions on the free and adsorbed enzyme, h) Secondly, if the state of H^O around the 

 active center is different in the case of adsorbed enzyme, would you not expect the 

 type of results you presented? 



Dr. McLaren: a) Trypsin on kaolin is inhibited by crystalline soybean-trypsin- 

 inhibitor in the same way and to the same extent as in solution. Also, both trypsin and 

 chymotrypsin are known to have only single active centers per molecule (E. Jansen 

 et id. /. Biol. Chan., 1949). /') The thickness of the layer of strongly bound water 

 on kaolin is doubtless much thinner than the diameter of the protein molecules 

 (McLaren, Peterson and Barshad. Proc, Soil Sci. Soc. .hucrica, 1958). 



Dr. Marshak: How do you explain the mobility of the enzyme molecules on the 

 surface of kaolin? Would you expect in terms of this interpretation that the mobility 

 on the siu'faces would be the same as that in bulk, as I untlcrstood you to say? 



Dr. McLaren: It has been shown that the adsorption of an enzyme on kaolin involves 

 an exchange of surface cations by the enzyme (McLaren, /. Phys. Chem., 1954). The 



