337 



Polypeptides and Related Compounds 



CXJ 



CH2— CH— COOH 



1 

 NH, 



Tryptophan 



CO— CHo— CH— COOH 

 NHo 



NHo 



Kynurenine 



CO— CH.— CH— COOH 



I 

 NH, 



3-Oxykynurenine 



It is likely that the peptide side-chain is attached before conden- 

 sation to form the chromophore. 



COOR 



COOR 



COOR 



OH 



CH3 



3-Oxy-4-methyl- 



anthranilic Acid 



(R = Polypeptide 



Moiety) 



Actinomycins 



It is interesting that methyltryptophans (a,5,6-methyls) are 

 inhibitory to actinomycin production. Methionine is probably 

 the donor of the methyl groups in N-methylvaline and sarcosine.^ 



In two streptomycete species D-valine inhibits actinomycin 

 synthesis while L-valine stimulates it, although D-vahne is the 

 isomer present in the side-chains.^ This behavior is reminiscent 

 of the results of similar earlier experiments with penicillin and 

 with valinomycin. 



Schmidt-Kastner found that addition of a large quantity of 

 sarcosine to the medium caused replacement of part or all of the 

 side-chain proline by sarcosine. Analogously, addition of isoleu- 

 cine caused replacement of N-methylvaline by N-methyhsoleu- 

 cine.'' Since then many new actinomycins have been prepared 

 by addition of various amino acids to the medium. Even 



^ G. Schmidt-Kastner, Naturwissenschaften 43 131 (1956). 



