6o SUBCELLULAR PARTICLES 



been hitherto employed should not be applied to the peroxidase models, as the 

 highest degree of specificity and the point of greatest interest involve formation of 

 a product with lowest degree of polymerization possible. On the other hand, the 

 importance of spatial orientation in phenol dehydrogenation reactions has been 

 recognized (6). The lack of structural similarity among the several substances 

 forming purpurogallin makes impossible any conclusion about surface structure 

 requirements for its synthesis. Nevertheless, it will be possible in the future to 

 explore in detail the specific catalysts, to modify constitution, crystal structure, 

 and the characteristics of the reaction medium, with the hope of arriving at in- 

 organic catalytic models accounting for the properties of an enzymic surface. 



CONCLUSIONS 



The development of model systems making use of reaction-directing surfaces 

 has revealed a powerful tool for investigation of biopolymer synthesis and the 

 nature of stereospecific synthesis by enzymes. In principle, no surface upon or 

 within a cell can be assumed a priori to be inert from the standpoint of matrix or 

 catalytic activity. Indeed, it would be difficult to prove that any macromolecule, 

 crystal surface, or, for that matter, phase boundary, within the cell is genuinely de- 

 void of such properties. Among the consequences of such widespread reaction- 

 directing properties will be a far more commonplace localization of chemical re- 

 actions than may be represented by those associated with organellar systems, and 

 a dependency of some biochemical reactions upon catalytic entities of a non-protein 

 (hence nonenzymic) character or upon proteins not now associated with enzyme 

 activity. Viewed in another manner, distinctions between structural and functional 

 cellular components must become highly arbitrary, and possibly misleading, and 

 in effect reduce many biochemical problems to questions of molecular morphology 

 and molecular interaction. 



The flexibility of the matrix concept encompasses a host of interactions of 

 organic or inorganic surfaces, crystalline or polymeric, with organic substrates, 

 and may be extended to systems including inorganic substrates whose behavior is 

 determined by organic surfaces, as in the mineralization of cartilaginous skeletal 

 substances, or secretion of highly intricate cell walls among diatoms, Radiolaria, 

 etc. 



The matrix and catalytic systems investigated determine the synthesis of lignin, 

 melanin, or purpurogallin, hence have substrates or monomers of a particularly 

 reactive type from the standpoint of free radical formation and ease of activation 

 for nuclear or nucleus-sidechain coupling. In principle, however, appropriate sys- 

 tems can be developed to serve as models for directed condensation polymer for- 

 mation, thereby extending further the scope of the matrix concept. The matrix- 

 substrate and peroxidase-mimicking systems discussed here show that the con- 

 stitution of the matrix may be of importance in specific cases, but that equivalent 



