66 METABOLISM 



coli and staphylococci, were unable to grow in solutions of pure egg albumin, 

 or of serum jDioteins, but that Proteus vulgaris was able to break down such com- 

 plex proteins provided that a sufiicient supply of nitrogen in an assimilable form 

 was added to the medium. Similar results have been recorded by Rettger and 

 his colleagues (Sperry and Rettger 1915, Rettger, Berman and Sturges 1916, 

 Berman and Rettger 1918). Of several gelatin-liquefying bacteria studied by 

 Berman and Rettger, none could utiUze egg albumin in the absence of other sources 

 of nitrogen. Only three species, B. suhtilis, Chr. prodigiosum and Proteus vulgaris, 

 could break down peptone. With proteoses purified by precipitation, B. suhtilis 

 and Chr. j^^'odwo^''^'''*^ caused complete breakdown. Only B. subtilis, Chr. prodi- 

 giosum and Proteus vulgaris could attack casein. B. subtilis and Chr. prodigiosum 

 could not only liquefy gelatin, but could use it as a source of nitrogen ; but such 

 organisms as Staph, aicreus or Bad. cloacse, although they caused rapid lique- 

 faction of the gelatin when provided with another source of nitrogen for growth, 

 showed no ability to ulitize the liquefied substance. 



The initial stage of Hquefaction of protein gels like coagulated serum or gelatin 

 is brought about by proteinases that, by opening the peptide linkage, reduce the 

 protein to polypeptides and dipeptides. The bacterial proteinases are readily 

 separated from culture by filtration, and apparently act extracellularly. The 

 breakdown into constituent amino-acids is effected by polypeptidases and dipepti- 

 dases. The peptidases have been studied in yeasts, but, being apparently for 

 the most part intracellular, they have as yet received no extensive study in bacteria, 

 for, as noted on p. 53, adequate methods of extraction of intracellular enzymes 

 have not long been available. 



Many of the anaerobes are conspicuous for their ability to break down complex 

 proteins, and the method of cleavage has been studied by several workers (Wolf 

 and Harris 1918, Harris 1919, Wolf 1919a, h ; see also Weil and Kocholaty 1937, 

 Kocholaty, Weil and Smith 1938, van Heyningen 1940). From a study of the 

 proteinases of Chr. prodigiosum, Ps. pyocyanea and Ps. fluorescens liquefaciens, 

 Maschmann (1937) concluded that enzymes of the different bacteria were identical, 

 but were not of the same type as the animal proteinase trypsin or the plant 

 proteinase papain. 



The hydrolytic degradation of protein is apparently due to the action of sj^ecial- 

 ized enzymes, which are produced in adequate amount when the bacteria con- 

 cerned are supplied with immediately assimilable food material, including nitrogen ; 

 during their consequent growth they are able to produce sufficient enzyme to 

 initiate protein cleavage and thereby increase the available nitrogen. 



Bacteria utilize amino-acids in a variety of ways, similar in extent and complexity 

 to those that have been described for the utilization of carbohydrates. As in our dis- 

 cussion of those substances, we can do no more than not« some of the biochemical processes 

 concerned ; for greater detail the student is referred to the monograph of Stephenson 

 (1939) and the review of Gale (1940). The amino-acids may be deaminated to yield the 

 corresponding hydroxy acid, by desaturation at the a-^ Unkage to give the unsaturated 

 acid, by reduction to give the saturated acid, by reduction and decarboxylation to give 

 the hydrocarbon ; or by oxidation. Decarboxylation results in the corresponding amine. 

 Neither decarboxylation nor deamination are processes yielding much energy, and in 

 bacteria with alternative energy-yielding mechanisms, like the streptococci (see Ehris- 

 mann and Dramburg 1937), the reactions are not important in the bacterial economy. 

 Where the amino-acid is one of the chief sources of food, oxidation to compounds with 

 fewer carbon atoms provides the requisite energy for synthesis, etc. The formation of 



