CHAPTER XVIII 

 THE PROTEINS OF MICRO-ORGANISMS 



THE proteins are essential constituents of all living 

 cells and are perhaps the most important as well as 

 the most complex substances synthesised by micro- 

 organisms. In spite of this, however, they can be built 

 up by certain organisms from the very simplest of starting 

 materials. For instance, B. aminovorans can thrive on 

 methylamine, in the absence of light, as its sole source of 

 carbon, nitrogen and energy, producing from it complex 

 proteins, carbohydrates and fats. The proteins, because 

 of their complexity, their colloidal nature and the lack 

 of any criterion of purity, are the most difficult of sub- 

 stances to study chemically, and we loiow comparatively 

 little of their internal make-up. We know that they are 

 built up of amino -acids joined together through the 

 carboxyl group of one and the amino group of the next 

 to give peptide linkages : — 



R.CH.(NH2).COOH+NH2.CH.R > R.CH.(NH2).C0.NH.CH.R. +H0O. 



COOH COOH 



The process is repeated, an amino-acid joining on to the 

 dipeptide first formed to give a tripeptide, and this taking 

 up another amino-acid and so on until polypeptides, 

 protamines and, ultimately, proteins are formed. The 

 proteins have very high molecular weights ; according to 

 Svedberg's findings they ai'c multiples of about 34,000 

 or 35,000. 



32S 



