58 METABOLISM 



He noted that it would be difficult to picture any reaction by which a single amino- 

 acid could break down anaerobically to yield energy, and that the most probable 

 reaction would involve two amino-acids, hydrogen being transported from one 

 to the other by the action of the bacterial enzymes. The general type of such 

 a reaction might be represented as 



ECHNH2COOH + R'CHNHa-COOH + H^O 



-> R-CO COOH + R'-CHg COOH + 2NH3. 



Stickland demonstrated paired oxido-reductive deaminations of this kind between 

 alanine and proline, cysteine and arginine. Woods (1936) suggests that, since 

 these coupled reactions occur at a rate similar to those of aerobic oxidations, 

 they may constitute an important part of the respiratory mechanism of the cell. 

 The same type of activity has been observed in CI. hotulinum, but not in CI. tetani, 

 which attacks amino-acids singly (Clifton 1940, 1942). Another energy-yielding 

 decomposition was described by Woods and Clifton (1937, 1938), an anaerobic 

 oxidative deamination of amino-acids by CI. tetanomorphum, in which no hydrogen 

 acceptor is required, since molecular hydrogen is produced as one of the end- 

 products. Hoogerheide and Kocholaty (1938) confirmed the evidence for coupled 

 Stickland reactions in CI. sporogenes, and found in addition that gaseous hydrogen 

 can be utilized by the organism, certain amino-acids acting as hydrogen acceptors 

 (see also Woods and Trim 1942, Guggenheim 1944). 



As with carbohydrates, our knowledge of protein metabolism is confined mainly 

 to relatively simple systems involving decompositions, and to defining the species 

 of bacterium, and the conditions in which these decompositions take place. Of 

 protein synthesis we know very little, except that it may be catalysed by enzymes 

 that our methods of study have hitherto revealed as concerned only in decom- 

 position. The enzyme aspartase in Bad. coli, for example, which deaminates 

 aspartic acid to give fumaric acid and ammonia, will in suitable conditions catalyse 

 the formation of aspartic acid from ammonia and fumaric acid (Cook and Woolf 

 1928). 



The Action of Bacteria on Fats. — It has long been known that many bacteria 

 are able to decompose fats (see von Sommaruga 1894, Rubner 1900, Eijkman 

 1901, Carriere 1901, Schreiber 1902, Orla-Jensen 1902, Huss 1908, Sohngen 1911, 

 Wells and Corper 1912, Kendall et al. 1914, Avery and CuUen 1920, Stevens and 

 West 1922, MichaeUs and Nakahara 1923, Neill and Fleming 1927, van der Walle 

 1927, Collins and Hammer 1934). The bacterial lipase induces a simple hydrolysis 

 into glycerol and fatty acid (Trussell and Weed 1937), and, under suitable con- 

 ditions, the glycerol is further decomposed and the fatty acid oxidized (see Harden 

 1930). 



Lipolytic activity is displayed by many parasitic and pathogenic species, 

 such as Bad. coli, Staph, aureus, streptococci, the pneuraococcus and the tubercle 

 bacillus, as well as by saprophytic organisms. But, here as elsewhere, there seem 

 to be wide differences in activity between different bacteria. Many of the parasitic 

 forms are feebly lipolytic, while certain saprophytic species, such as the bacterium 

 isolated by Huss (1908) from milk, are extremely active. 



The actively lipolytic bacteria are of considerable industrial importance, since 

 they cause rancidity in butter and other fat-containing foods. It is possible, also, 

 that such species play some part in sewage-purification. 



It may be noted, in connection with the fat metabolism of bacteria, that one 



