SELMAN A. WAKSMAN 269 



of the enzyme; the same is true of Fischer's idea that enzymes possess a protein 

 nature, the work of Willstiitter having established that some enzymes at least (lipase, 

 peroxydase, invertase) can be purified to such an extent that the protein reactions 

 disappear completely. Some enzymes were obtained practically free from iron and 

 phosphorus. Nitrogen seems to be an essential constituent, the purest invertase con- 

 taining 13 per cent and peroxydase 9.37 to 13.37 pcr cent nitrogen. According to 

 Euler, this is proof of the protein nature of enzymes. According to Willstatter, the 

 proteins are merely impurities which cannot be readily removed. 



Enzymes are thus considered' to be composed of a specifically active group and 

 a colloidal carrier, the latter varying in its nature but essential for the stability of the 

 active group. A theory has also been advanced^ that various enzymatic reactions 

 brought about by bacteria are primarily due to polarizations of substrate molecules 

 induced by electric fields which characterize particular centers of cellular and intra- 

 cellular surfaces, these being "active centers"; one active center may be able to 

 activate various substrates, the structure of a molecule influencing its activation. 



CLASSIFICATION 



According to Neuberg and Oppenheimer, enzymes can be divided into two large 

 groups: (i) Hydrolases, which bring about hydrolytic decomposition. There is only 

 a very small gain of energy in these reactions. Here belong the esterases which act 

 upon fats and esters, the carbohydrases which act upon carbohydrates, the proteases 

 which act upon proteins, the amidases which act upon the amide and amino groupings. 

 (2) Desmolases, which influence the bonds of atoms. They break the carbon chain 

 with the liberation of free energy. They are the enzymes of respiration and of metabo- 

 lism. Here belong those enzymes which bring about the various oxidation and reduc- 

 tion processes, the fermentation reactions (anaerobic), as well as the important 

 enzymes zymase and catalase. 



FORMATION AND SECRETION OF BACTERIAL ENZYMES 



The enzymes of bacteria have been very insufficiently studied. In most instances, 

 analogies must be drawn with animal and plant enzymes, or enzymes of other micro- 

 organisms. The recent investigations of Meyerhof and others on respiration and 

 fermentation have shown that such analogies are usually justified. 



A bacterial cell is able to elaborate at least two distinct types of molecules, name- 

 ly, highly specialized molecules which exhibit enzymatic behavior, and non-enzymatic 

 substances; these together make the protoplasmic and histological cell structures, 

 and are inseparably connected with one another.^ 



Many enzymes are produced in an inactive condition, namely, as proenzymes or 

 zymogens, and are changed into the active form by an activator. This activator may 

 be merely an acid or an alkali necessary to adjust the reaction to the optimum for 

 the particular enzyme, as in the case of pepsin or lipase. In some instances, electro- 

 lytes (NaCl) are essential, anions being active in the case of diastase, and cations such 



•Willstatter, R.: J.Chem. Soc, p. 1374. 1927. 



^ Quastel, J. H., and Wooldridge, W. R.: Biochem. J., 21, 1224. 1927. 



3 Quastel, J. H., and Wooldridge, W. R.: ibid. 



