ENZYME REACTIONS AT SURFACES 



29 



TAm.F. 2. Situations in which one iinus an iniluhnce of A pii on unzyme acii\h\ in 



SOLUTION COMPARED WITH ACTIVITY AT A SUKIACU * 



ENZVME ON PARTULE 

 OR SURFACE 



(",li\ inotrypsin on adsorbed protein 



Yeast surface 

 Invcrtase 

 'Phosphorylasc' 



Surfaces of odier microorganisms 



Ascorbic acid oxidase of M. vernicaria (spores) 

 Invertasc of A/, rernicaria (spores) 



Roots 



Barley-cell wall ascorbic acid oxidase (hoinogcnates 



vs root segments) — 0.2 (22) 



Wheat-Cell wall invertase see table 3 (3) 



* Activity at surface — activity in bulk: A pH. 



soil structural elements one must consider that the activity of the soil enzymes 

 will not be of the same relative reactivity as would be found for the study of the 

 same enzymes in solution. A coinparison of chymotryptic activity in solution versus 

 that on a surface (cf. fig. 2) at pHi, = 7 could lead one to conclude that adsorbed 

 enzyme is inactive, or nearly absent (see ref. 32 for a study of soil urease). Failure 

 to take this phenomenon into consideration may lead to questionable conclusions 

 about the degree of enzyme activity (16). Zittle has reviewed this subject (49). 



Action of Cell Surface Enzymes in Vivo and in Vitro. For the yeast Saccharo- 

 myces cerevisiae, ApH is calculated to be 0.30 (in m/ioo acetate or phthalate); 

 table 2 (26, 47). 



A number of enzymes are supposed to be near or at the cell wall of yeast (42); 

 table 2. For one of these, invertase, a ApH of 0.3 has been determined from rate 

 studies of yeast and cell free enzyme; see figure i (48). A difference in pH^ and 

 pHij for Bacterium coli has been computed from microphoretic measurements 

 (fig. 3) and such differences may apply to 'permease,' dehydrogenase, and other 

 enzymes which may be acting at bacterial cell surfaces.* It is clear from tables i 

 and 2 that the displacement of pH optima for enzyme action at cell surfaces is 

 not always as expected; i.e., is either zero or in the opposite direction. Unknown 

 factors other than a negatively charged surface must be involved. (The direction 

 of displacement could be toward lower pH for a positively charged surface; how- 

 ever, such surfaces seem to be rare or as yet infrequently observed in nature. They 

 have been achieved artificially, however, and with the expected influence on 

 I.T.(7).) 



■* For cations, the 'reversal of charge concentrations' has been plotted in the form of spectra 

 for E. coli and compared with similar spectra for naturally occurring high polymers. The 

 exterior of cells has thereby been surmised to contain polysaccharide. 



