SUBSTANCES PRODUCED BY BACTERIA 187 



like gramicidin, it precipitates a number of soluble proteins in a manner 

 similar to some of the cationic detergents. 



Tyrocidine is dissolved in four times its weight of boiling absolute 

 alcohol, to which is added alcoholic HCl (o.i mol. per liter). On cool- 

 ing, a precipitate is formed. This is recrystallized from absolute metha- 

 nol plus small amounts of HCl ; clusters of microscopic needles are ob- 

 tained, melting at 237-239° C, with decomposition; the specific rota- 

 tion is [a]^5 = — 102° ( I per cent in 95 per cent alcohol). Tyrocidine 

 analyzes: 59.4 per cent C, 6.8 per cent H, 13.5 per cent N, 2.7 per cent 

 CI. The molecular weight is about 1,260 or a multiple of this number. 

 Tyrocidine is a salt of a polypeptide having free basic amino groups. 

 The ^-amino acids make up 20 per cent of its a-amino groups. The most 

 probable molecule was shown to contain two amino groups, three amide 

 groups, and one weakly acidic carboxyl or phenolic group, with a molec- 

 ular weight of 2,534. Among the amino acids, tryptophane, tyrosine, 

 and dicarboxylic-amino acids have been detected j concentration of some 

 of these acids has been established: aspartic acid, 5.1 per centj valine, 

 7.6 per cent J and leucine, 8.2 per cent (138, 140). Summaries of the 

 chemical and biological properties of gramicidin and tyrocidine were 

 made by Hotchkiss (449) and Hoogerheide (443). 



The tyrothricin-type of antibiotic substance appears to be widely dis- 

 tributed among spore-forming aerobic soil bacteria (442, 444, 885). 

 Preparations obtained from different bacteria appear to be markedly 

 different in chemical nature and biological activity. This is true, for 

 example, of the preparation obtained by the following method: A 

 seven-day-old bacterial culture was treated with 2 to 5 per cent of an 

 electrolyte and HCl added to give a fH of 4.0. A precipitate was 

 formed which was centrifuged and extracted with 95 per cent alcohol, 

 until no more turbidity could be observed after dilution with an equal 

 volume of water. The alcoholic extracts were evaporated to dryness and 

 extracted with ether, petroleum ether, and benzol, in which the active 

 substances are insoluble. The residue was then dissolved in absolute 

 alcohol, and the concentrated solution dialyzed for 24 hours against 

 running tap-water and for 24 hours against distilled water. The active 

 substance was obtained partly in a precipitated form and partly in a 



