CATALYSIS: THE GUIDE OF LIFE 117 



the biocatalyst. Often the prosthetic group demands for its func- 

 tioning the presence of a single atom, e.g., magnesium with 

 chlorophyll, copper in the polyphenol oxidase of mushrooms and 

 in tyrosinase, iron in catalase, cytochrome, etc. Where "homeo- 

 pathic" doses are effective, their action may often be understood 

 along these lines. 



Richard Willstatter 35 proposed the term symplex for compounds 

 where high-molecular substances are bound by residual valencies, 

 e.g., a prosthetic group and a colloidal carrier. Symplexes are 

 distinguished from mere mechanical mixtures by one or more of 

 the following characteristics: (1) alteration or enhancement of 

 specific reactivity of one component; (2) change in solubility or 

 dispersion of one component; (3) change in optical properties; 

 (4) change in stability; (5) change in toxicity; (6) change in reac- 

 tions, e.g., color reactions. 



True chemical combination is not necessary to make separate 

 units acquire new properties when combined. Neither an arrow- 

 head, an arrow shaft, nor a goose feather is an arrow; but the 

 three, when properly fitted together, will make an arrow and will 

 function as one. 36 



Structures of the "symplex" type are very loosely bound together. 

 E. L. Smith 37 found that solutions of phyllochlorins (chlorophyll- 

 protein compounds extracted from spinach leaves) may be split into 

 free chlorophyll and protein by the detergents sodium desoxycholate, 

 bile salts (mainly sodium glycocholate) and digitonin. In the presence 

 of sodium dodecyl sulfate (SDS), the prosthetic group remains at- 

 tached to the protein, but the compound is split into smaller units, the 

 protein properties and absorption spectrum being modified. Tobacco 

 mosaic virus is also split by SDS into smaller fragments, nucleic acid 

 being simultaneously separated from the protein. 38 In the presence of 

 SDS chlorophyll loses magnesium and becomes phaephytin; and this 

 substance, or the chlorophyll (depending on pH), remains attached to 

 the protein, since the prosthetic group is not separated by ultra-filtra- 

 tion, dialysis, or fractional precipitation. Smith believes that much 

 previous work on chlorophyll dealt only with the prosthetic groups of 

 extremely complex specific catalysts. Emerson and Arnold 39 con- 

 cluded from photochemical studies that 2,500 chlorophyll molecules 

 form one functional unit in photosynthesis. 



The importance of the carrier in the biological field is indicated by 

 the following two examples. Keilin and Mann 40 report that per- 

 oxidase, which shows great resemblance to methemoglobin, can be 

 considered as a compound of protohematin with a native protein. 



