ACTION OF ENZYMES 49 



induce, they differ in that they require external energy in order 

 to do their work ; instead of causing energy to be given out from 

 the chemical system, they cause the system to take up energy, 

 and instead of assisting the system towards the equilibrium point 

 towards which it tends in their absence, they cause a movement 

 away from the equilibrium point. 



To this class of catalysts the living cells of plants and animals 

 belong, and although the process is most clearly seen where 

 chlorophyll is present, and is masked in other cells by preponderating 

 action in the opposite direction, there is probably no cell in which 

 anabolic processes do not occur, as shown by the building up, 

 accompanied by storage of chemical energy, of complex organic 

 substances, such as the organised proteid or protoplasm of the 

 cell, and the granular deposits in the cell of amyloses, fats, and 

 other reserve food-stuffs, from the soluble constituents of the 

 plasma or of the circulating fluids by which the cell is nourished. 

 In most types of cell the energy required for the anabolic pro- 

 cesses is derived from chemical energy obtained by an oxida- 

 tion process affecting a portion of the nutrient matter ; the 

 energy obtained from this reaction being used to run the anabolic 

 reaction. 



The linkage together in this way of a variety of complex chemical 

 reactions is what distinguishes the cell as an energy-transformer 

 from the simpler acting soluble enzyme, which is so often a product 

 of its activity. Such linkage of reaction is never seen in the case 

 of enzymes, which are exceedingly fixed and selective in their 

 action (see p. 114). The enzyme acts usually upon one type of 

 molecular arrangement only, often failing in attacking even the 

 stereo-isomer, but the cell carries on a wide commerce of reaction 

 with many types of matter, and modifies the reactions in many 

 varied ways ; and also differently at different periods according 

 to its condition, and the manner in which it is affected by con- 

 current reactions taking place in other cells in the body, or by 

 the influence of the nervous system upon it. 



Actions similar to those of the cell in storing up chemical energy 

 are also seen in physical transformers ; an example of such is 

 the synthesis of compounds by the electric current and the 

 electrolysis of conducting solutions. Here the electrodes, two 

 conductors at different potentials, act as energy-transformers for 

 converting electrical into chemical energy. 



D 



