Some Characteristics of Enzyme 

 Reactions at Surfaces^ 



A. D. McLaren and k. l. babcock 



College of Agriculture 



University of California 



Berkeley 



TT HAS LONG BEEN RECOGNIZED that eiizyme reactions may be influenced by the 

 structural heterogeneity and surface properties of cells. The nutrition of 

 cells, as of microbes and plant roots in soil or of bacteria on teeth, for example, 

 also involves enzyme activity at interfaces. Since natural interfaces are often 

 charged, the effective concentrations of hydrogen ions, sulfhydryl groups and 

 anions at interfaces are generally different from those in adjacent bulk media. 

 Thus, enzyme reaction rates involving requisite concentrations of ions or redox 

 [potentials for the enzyme will be quantitatively different for bulk and interfacial 

 systems. In structured systems such as mitochondria one may ask, for example, 

 whether for the electron transport chain from succinate to cytochrome c the 

 spatial arrangement in the original subcellular particle is so exacting that ran- 

 dom collision between the component proteins, or even coadsorption on a suitable 

 carrier, will be able to re-establish the original sequence of events with anything 

 approaching the efficiency of the natural practiculate complex (45). 



Although the theory of enzyme reactions /;; I'itro has progressed phenomenally 

 in the past decade, the biological implication of this progress is not straight- 

 forward and an even greater effort will have to be placed on the in vivo aspects 

 before these theories are fully justified. A few schools have been keeping the 

 goal in sight, among which are A. Rothstein and co-workers ( 1 8, 41) with cell 

 surfaces and B. Chance (5) with intracellular reactions. 



SIGNIFICANCE OF A DIFFERENCE BETWEEN SURFACE pH AND BULK pU 



In 1937 Danielli wrote, "The bulk of the fluid contents of the cell are pre- 

 sumably of fairly uniform reaction, but the surfaces of granules, oil globules, 

 mitochondria, and gel particles may well differ from the bulk reaction by up 

 to 2 pH units, according to the constitution of the surfaces concerned. The cell 

 may thus offer a much more diverse environment for enzyme reactions than 

 has hitherto been supposed." Also, with an acid interface, variation of cation 

 concentration "may produce an effect very similar to variation of the pH" (7). 



1 Supjiortcd in part by a research >;rant (G-^236) from the National Institutes ol Health. 



