UNITY AND DIVERSITY IN THE METABOLISM OF MICRO-ORGANISMS 



zymes that frequently can be quantitatively separated from the cells, 

 whereas the former have tenaciously resisted the efforts to isolate the 

 causative enzymes. It is true that Buchner has succeeded in extracting 

 a very small fraction of the fermenting capacity of some specific 

 yeasts from the cells, but various arguments can be adduced in favour 

 of the statement that in those instances the prominent dissimilation 

 catalysed by the living protoplasm is accompanied by a weak sugar 

 fermentation proceeding under the influence of a zymase function 

 that can be isolated in small amounts. This concept is strengthened 

 by the rather ridiculously low yield that Buchner and his collabora- 

 tors, Gaunt and Meisenheimer [1906], obtained in their attempts to 

 isolate a lactozymase and an alcoholoxidase from lactic and acetic 

 acid bacteria, respectively. In spite of this, they interpret their results 

 as supporting their enzymatic theory of metabolism. Similarly, the 

 old controversy as to whether the urea decomposition by urea bacte- 

 ria does or does not proceed under the influence of a soluble enzyme, 

 urease, thus appears in a new light. From the genuine urea bacteria, 

 for which the decomposition of urea indubitably is also a dissimilatory 

 process, a separation of urease is practically impossible, as Beijerinck 

 has already shown. In other organisms the splitting of urea appears 

 virtually to have lost its energetic significance, in view of the occur- 

 rence of other dissimilatory processes. Thus it becomes understandable 

 that Jacoby [191 7, 1923] succeeded in isolating a soluble urease from 

 Proteus bacteria ; this he would certainly not have accomplished had 

 he used Urobacillus pasteurii. * 



I do not have the opportunity to dwell much longer on the con- 

 cepts that arise out of the energetic considerations of metabolism. 

 That it would undoubtedly be extremely rewarding to submit the 

 entire problem of microbial metabolism to a renewed study in con- 

 nexion with the second law of thermodynamics may here be hinted 

 at. The great significance of this problem for general physiology has 

 been pointed out by Zwaardemaker [1906]. Application of these 

 principles to the relatively simple situation in microbes has hardly 

 been begun thus far; nevertheless, it should almost inevitably be pro- 

 ductive of significant results. 



* The ready solubility of soybean urease is undoubtedly closely linked to the fact 

 that the decomposition of urea is energetically insignificant for the cells of higher 

 plants because their mode of life is predominantly oxidative. 



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