182 UNITY AND DIVERSITY IN BIOCHEMISTRY 



medium is buffered and the slice is sufficiently thin (0-3 mm approx.) this 

 method is very useful. Thanks to the manometric method developed by 

 Warburg, the use of tissue slices has given much important information. 



The next stage in the order of gradually increasing destruction is the use 

 of minces, breis and homogenates. Here, the cells are destroyed but the 

 intra-cellular particles are intact. They may even be isolated by centri- 

 fugation, and mitochondria are often separated in this way. However, 

 although all the above methods are useful and instructive, only the results 

 obtained with purified enzymes have been capable of giving precise infor- 

 mation about metabolic mechanisms. The rapid progress of biochemistry 

 during the course of the last few j^ears is primarily the result of the perfecting 

 of methods for the isolation, purification and characterization of enzymes. 



If the results so obtained are clear and precise, they are evidently also 

 reached through the most extreme of destructive processes and the re- 

 constitution of the complex phenomena of metabolism from such results 

 might appear, and in fact does appear to certain intellects, a most far- 

 fetched undertaking. 



As enzymology was developing, biochemistry also was shaking off the 

 shackles imposed upon it by chemists on the one hand, and physiologists on 

 the other. As the particular nature of its own problems became apparent, 

 biochemistry began to explore all the paths of Nature in search of their 

 solution, breaking open the compartments into which an out-of-date 

 classification of the sciences had tended to confine it. Having recourse to 

 recent discoveries in physics and genetics, the biochemists took the cer- 

 tainties obtained from the use of purified enzymes, and with indications 

 provided by the use of isotopes and mutant forms of micro-organisms they 

 developed new non-destructive methods to go with the extremely de- 

 structive methods of enzymology. It is due to this combination of ingenuity 

 and patience that numerous problems of biosynthesis, up till then obscure, 

 have been solved. 



II. BIOCHEMICAL INVESTIGATION AND THE 

 USE OF ISOTOPES 



By means of isotopes it is possible to mark a compound at one or more 

 positions in the molecule and to follow the fate of these labelled atoms. With 

 the introduction of isotopes of the most common elements in the biosphere 

 (hydrogen, carbon, nitrogen, oxygen, phosphorous, sulphur), the method 

 has proved most fruitful. 



REFERENCES 



Neilands, J. B. and Stumpf, P. K. (1955). Outlines of Enzyme Chemistry. Wiley, 

 New York. 



