PROTEINS 



109 



lysergic acid 



L-phenylalanine 



ergotamine 



tide alkaloid from lyc ergot. Ergot is a iungiis infesting rye and pro- 

 ducing toxic symptoms in animals that ingest it. Of the four com- 

 ponents in this structure, L-o-proline is unknown in free form, being a 

 member of the group of ortho acids known from their derivatives and 

 represented with carboxyl groups in the completely hydrated form 



OH 



I 

 — C— OH 



I 

 OH 



Members of another large group of peptides possess antibacterial 

 activities and occur in many materials, most of the known cases being 

 from fungi and bacteria. Many are powerful antibiotics but most are 

 too toxic for medical use. However, the group does include the peni- 

 cillins. Penicillin G is the most common and may be written thus: 



CH3 H 



CH,— C C — COO" Na"^ 



--k I 



ri n ' 



>\ / 



H nh;occh^ 



where the dotted lines arc used to reveal the components. The top 

 portion has the structure and configuration of D-valine, the middle part 

 is D-cysteine, and the lower component is phenylacetic acid. The other 

 penicillins possess analogous structures but with different acids in 

 amide linkage with the cysteine. Two of the rings are formed by the 



