26 IMMUNO-CATALYSIS 



during the activity of its life-cycle. It would therefore seem quite reason- 

 able to assume that the special physiology of each type of cell is 

 controlled by the specificity of the cellular enzymes. It is to be noted, 

 however, that the catalytic activity of an isolated enzyme is generally 

 independent of the living processes of the cell which produce it, 

 although the activity of such an enzyme as part of the cellular system 

 may be different, or a great deal more active, than when it acts as a 

 single isolated chemical entity. 



Crystalline Enzymes. Pasteur and his followers regarded the cata- 

 lytic activity of biological systems as an inseparable part of the 

 phenomenon of life, and outside of experimental science. Liebig 

 challenged Pasteur's point of view and advocated the existence of 

 enzymes outside of the cell. Biichner in 1897 settled the argument 

 finally by demonstrating that the fermentation of sugar could be 

 caused by yeast extracts free from living cells; since then, not only 

 many cell-free enzyme preparations have been obtained, but a score 

 of enzymes has been obtained in crystalline form, which fact estab- 

 lishes, beyond doubt, the chemical individuality of enzymes. Crystal- 

 line urease (Sumner, 1926) was the first enzyme obtained in 

 crystalline form. Later many crystalline enzymes and their precursors 

 have been obtained and their purity studied by critical methods. 

 They are: fefsin (Northrop, 1930); amylase (Caldwell, Booher and 

 Sherman, 1931); yellow enzyme (Warburg and Christian, 1932; The- 

 orell, 1934); Chymotrypsin (Kunitz and Northrop, 1935); carhoxy- 

 -peptidase (Anson, 1935); ficin (Walti, 1937); papain (Balls, Line- 

 weaver and Thompson, 1937); lysozyme (Abraham and Robinson, 

 1937); catalase (Sumner and Bounce, 1937); alcohol dehydrogenase 

 (Negelein and Wulff, 1937); tyrosinase (Dalton and Nelson, 1938); 

 lecithinase (Slotta and Fraenkel-Conrat, 1938); d-rihonuclease (Kun- 

 itz, 1939; muscle d-glyceraldehyde-3-phosphate dehydrogenase (War- 

 burg and Christian, 1939); yeast d-glyceraldehyde dehydrogenase 

 (Krebs and Najjar, 1948); muscle lactic dehydrogenase or pyruvic acid 

 reductase (Straub, 1940); peroxidase (Theorell, 1940); fumarase (Laki 

 and Laki, 1941); Rennin (Hankinson, 1942); phosphorylase (Green, 

 Cori and Cori, 1942); phosphate transporting enzyme, 1,3-diphos- 

 phoglyceric acid + adenosine diphosphate ^ 3-phosphoglyceric acid 

 + adenosine triphosphate (Schelling, 1942); myosin (Szent-Gyorgyi, 

 1943); serum mucoprotein with high cholinesterase activity (Bader, 



