BIOSYNTHESIS OF PROTEINS 269 



indicate that the bulk of the enzymes are associated with the 

 formed elements of the cell contents, which gives a special 

 character to the activity of these biocatalysts which is sub- 

 stantially different from that observed in simple aqueous 

 solutions of enzymes isolated from cells. It was thus estab- 

 lished that even slight changes in the composition of proto- 

 plasmic structures occurring under the influence of external 

 factors have a substantial effect on the speed and nature of 

 synthetic reactions within the living cell.^" 



Damage to or disruption of these structures, which occurs 

 under even the mildest conditions, leads to the complete 

 abolition of biosynthesis. For example, the bacterium Micro- 

 coccus lysodeikticus may be treated with lysozyme without 

 disturbing the structures in the least, if the lysis is carried 

 out in the presence of sucrose. ^^* When this takes place, the 

 protoplasts retain their ability to incorporate marked mole- 

 cules of glycine and leucine in their protein.^" However, it 

 has been shown in our laboratory that if the concentration of 

 sucrose is gradually lowered, a definite point is reached when 

 the concentration falls below 0-64 m and the structure of 

 the protoplasts is disrupted. This can easily be checked with 

 the electron microscope. At the same time there is a sharp 

 fall in the respiration of the protoplast, and later, when the 

 concentration of sucrose falls below 0-44 m, the protoplast 

 loses its ability to incorporate marked glycine and to syn- 

 thesise protein in the presence of a complete collection of 

 amino acids. ^^® Obviously there is a limit to the amount of 

 damage which the structure of the protoplast can suffer, 

 beyond which the biosynthesis of protein becomes impossible 

 owing to the loss of that co-ordination of the reactions in 

 time which only occurs when the enzymes are placed in 

 special positions relative to one another in the protoplasm 

 (Fig. 21). 



In recent years a large number of papers have appeared 

 showing how particular enzymes are associated with this or 

 that demonstrable structure, whether it be plastids,^^^ mito- 

 chondria or microsomes, ^^* and hence which biochemical 

 processes are localised in these formed elements of the 

 protoplasm. Thus it has been established that there are 

 concentrated in the mitochondria the enzymes taking part 



