168 CHEMICAL NATURE OF ANTIBIOTIC SUBSTANCES 



milliliter alcohol is diluted to i mg. per milliliter, with distilled water 

 or with glucose solution, an opalescent solution is produced without 

 flocculation. On dilution with electrolyte solutions, an immediate floc- 

 culation occurs. 



The specific rotation of gramicidin in 95 per cent alcohol solution is 

 approximately [a]^^ = -|- 5°. On analysis, it gives 62.7 per cent C, 

 7.5 per cent H, and 13.9 per cent N. The molecular weight, as 

 determined in camphor, is about 1,400. The empirical formula of 

 C74H106N14O14 has been suggested. On further study, the molecular 

 weight of gramicidin was found (885) to present an anomaly in that it 

 appeared to depend on the nature of the solvent and on the concentra- 

 tion of the solute, giving values from 600 to i,200j isothermal distil- 

 lation in methanol, however, indicated a molecular weight of 3,100. 

 Sulfur and carbon analyses of gramicidin flavianate gave a molecular 

 weight of 3,000. It gave neither free amino nor carboxyl groups (126, 

 434). Gramicidin is a polypeptide with 10 molecules of a-amino acids, 

 of which two or three are tryptophane residues. These and a saturated 

 aliphatic acid, with 14 to 16 carbons, account for about 85 to 90 per cent 

 of the weight of substance. Amino acids that have definitely been iden- 

 tified are /-tryptophane, <i-leucine, /-alanine, ^/-valine, and glycine 

 (339). A study of the configuration of the dipeptide valyvaline sepa- 

 rated from gramicidin brought out the fact that only valines of like 

 configuration have been joined together by the bacterium (125). About 

 45 per cent of the a-amino acids gave the d configuration (435, 436, 

 530). An unknown hydroxyamino compound has also been indicated 



(339)- 



Tyrocidine hydrochloride is moderately soluble in alcohol, acetic 

 acid, and pyridine ; it is sparingly soluble in water, acetone, and dioxane, 

 and is insoluble in ether and hydrocarbon solvents. An alcohol solution 

 can be diluted with water to give a clear solution containing 5 to 10 mg. 

 per milliliter j electrolytes produce an immediate precipitate. A solu- 

 tion in distilled water containing i mg. or even less per milliliter has a 

 low surface tension and behaves like a soap or detergent solution. Un- 

 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 



