CATALYSIS: THE GUIDE OF LIFE 131 



acetaldehyde is fixed by the sulfite, the C0 2 is liberated, and the 

 glycerin remains; during World War I Germany produced glycerin 

 by fermentation processes. Bell 82 states that the traces of glycerin 

 in normal fermentation are due to the "mutase" system in the 

 yeast cells. It seems that, normally, acetaldehyde acts as a hydro- 

 gen acceptor in the anaerobic oxidation of triose phosphate; but 

 when the acetaldehyde is removed by the sulfite present, another 

 molecule of triose phosphate can act instead. Since the former 

 reaction is the more rapid, little glycerin is formed when acetalde- 

 hyde is present. 



By carrying out the fermentation at an alkaline pH, Neuberg 

 found that the breakdown of the glucose yielded glycerin, alcohol, 

 and acetic acid, according to the following scheme, which is not 

 yet understood in detail: 



Glucose 



1 

 Triose Phosphate 



/ \ 



CO 2 + acetaldehyde 



1/2 Alcohol 

 l /2 Acetic acid 



Glycerin 



Not only does the apparently simple yeast cell contain a con- 

 siderable number of specific enzymic catalysts and collaborating 

 molecules, but it can be "trained" to ferment galactose, 83 by add- 

 ing small and continually increasing percentages of this sugar to 

 the fermentation mixture. Evidently yeast can "manufacture" 

 new enzymes to meet new situations; probably the new substances 

 add their own specificity to a system of molecules to make a new 

 prosthetic group. 



Modification of Biocatalysts 



The writer has taken the view that biocatalysts are subject to 

 modification, which involves the fixation, at an active catalyst area 

 of a gene or other catalyst unit, of some particle (electron, ion, 

 atom, molecule, or colloidal particle) which changes the nature 

 and/or the rate of the catalytic change occurring there. A limiting 

 case under this general principle would be the formation of a new 

 catalyst area by the fixation, e.g., at a protein surface, of a pros- 

 thetic group. In the case of genes a change in catalytic output 

 may arise from an intra particulate change in the gene itself 

 (known as a point mutation), or because of some chromosomal 



