DECOMPOSITION OF OEGANIC COMPOUND 229 



necessary in bringing about this combination, the reaction 

 may be written : 



CH^NH^COOH + CH^NH^COOH 



= NHjCH^CONHCH^COOH + H^O 



By the abstraction of a molecule of water, then, it is possible 

 to cause alpha-amino acids to unite with each other. The 

 resulting compound is called a peptid. An examination of 

 the structure of the peptid shows it also to be an amino 

 acid, that is, it contains an NHj and a carboxyl radical. It 

 is, therefore, possible to duplicate the preceding reaction 

 and cause peptids to unite with each other. If two dipeptids 

 unite, for example, the resulting compound will be made up 

 of four alpha-amino acid radicals joined together. This 

 process may be continued indefinitely. As many as sixteen 

 of these alpha-amino-acid radicals have been caused to join 

 to each other in laboratory studies. A complex compound 

 of this type is termed a polypeptid. In nature, undoubtedly, 

 polypeptids unite to form peptones, peptones to form pro- 

 teoses and proteoses finally to form proteins. 



Microorganisms in bringing about changes may attack 

 the proteins by adding water to the molecule and causing 

 them to break down into simpler proteoses. The proteoses 

 in turn may be hydrolyzed into peptones and these through 

 polypeptids and peptids and finally to the alpha-amino 

 acids. Such a change may be regarded as a digestive action 

 on the part of the microorganisms. Such changes are due 

 to the development of pepsin and trypsinlike ferments 

 which act externally to the cell of the microorganism, that 

 is, this is an example of the analytic action of an extra- 

 cellular enzyme. The amino acids thus formed as the result 

 of the activity of microorganisms may themselves be 

 attacked in various ways. One of the most important of 

 these is the process termed deaminization. Certain micro- 

 organisms have the power of removing the amino group, 



