16(3 BACTERIOLOGICAL CHEMISTRY 



bacteriostatic to Gram -positive bacteria. Gramicidin 

 has the property of depressing the surface tension of 

 aqueous sohitions ; the property is not lost on heating, 

 although the bacteriostatic and hsemolytic effects are 

 destroyed by heat. Gramicidin does not lose its bacterio- 

 static properties in the presence of serum. It will protect 

 mice from infection by Gram -positive organisms when 

 it is injected in contact with the organisms but not 

 otherwise. Gramicidin has been shown to detoxify 

 tetanus and diphtheria toxins. It is too toxic to be of 

 use for internal chemotherapy but has been used for 

 local application. Gramicidin has been shown to be a 

 closed ring polypeptide containing 24 amino acid residues, 

 having a molecular weight of 2790, m.p. 230 — 231°C., 

 [all? + 2-5°. It contains no free amino or carboxyl 

 groups. The amino acid residues comprise 6 of leucine, 

 6 of tryptophane, 5 of valine, 3 of alanine, 2 of glycine 

 and 2 of a hydroxy-amino compound, possibly ^<so-serine. 

 The leucine and two or three of the valine units are in 

 the d-iorm. It is resistant to the action of trypsin, 

 pepsin and papain. It is possible that the c?-amino acids, 

 very rarely found in nature, may be responsible for its 

 bacteriostatic properties. 



The action of formaldehyde on gramicidin greatly 

 reduces its toxicity and hsemolytic activity without 

 harming its bacteriostatic properties. The modified 

 gramicidin may possibly be used for internal therapy. 



Gramicidin- S. — A substance of a similar character 

 to gramicidin has been obtained by Russian workers 

 from a soil bacillus. Gramicidin-S is very stable to heat, 

 has m.p. 268-270°C. and molecular weight about 1250. 

 It is of peptide nature but contains free NHg and COOH 

 groups. It also differs from gramicidin in containijig 

 proline and ornithine but no tryptophane. It is different 

 in that it is bacteriostatic to some Gram-negative organ- 

 JiJ. typhosa at 50/Ag./m]., Sh. dysenterue at 



