473 



Thus, we see that the alpha, beta, and gamma types of amino 

 acids are determined by the distance that the NH2 radical 

 is separated from the COOH group. If there are two amino 

 radicals at different distances from the carboxyl group, the 

 amino acid belongs to both of the two types; thus, valeric 

 acid, CH3-CH2-CH2-CH2-COOH, when converted into diamino- 

 valeric acid, CH3-CH-(NH2)-CH2-CH(NH2).COOH, becomes 

 an amino acid of the alpha and gamma type. An amino acid 

 to be strictly and solely of one type can contain only one amino 

 group. Glycine is such a pure alpha type. The alpha type 

 of amino acid is by far the most common and important. Only 

 rarely does the beta type occur in nature. All of the acids that 

 are products of the hydrolysis of proteins are alpha amino acids. 



A definite number of amino acids, in specific arrangement, 

 build up each protein. The table shown on page 474 is the 

 constitution of egg albumin, the names, proportions, and chemical 

 constitution of the eight different amino acids being given. 



There are eight kinds of amino acids in albumin, but many 

 more than eight amino acid chains or molecules, for of each kind 

 there are from few to many units. A conservative estimate of 

 three molecules for the least abundant member — cystine — would 

 give a total of over 250 amino-acid chains in one molecule of 

 albumin. 



Synthesis. — Hydrolysis of the proteins causes them to break 

 down into their component parts. It should, therefore, be 

 possible to reverse the process and build up proteins by uniting 

 amino acids with the elimination of water. This is how Fischer 

 accomplished the synthesis of simple protein derivatives. The 

 first stage in such a condensation process results in the formation 

 of a dipeptide (glycyl-glycine). A third molecule of the same 

 amino acid, or a different one added by condensation, yields a 

 tripeptide. The most complex polypeptide yet produced is an 



