Polypeptin

Polypeptin—Polypeptin was purified, crystallized as its sulphate and characterized by Howell . By means of coxmtercurrent distribution, Hausmann and Craig determined the components as L-a,y-diaminobutyric acid, L-threonine, D-valine, L-isoleucine, L-leucine and D-phenylalanine in the molar ratio 3 1 1 2 1 and an unknown fatty acid . The molecular weight of the free base was found to be 1,145. The structure of polypeptin is still unknown. 

Methylootanoic acid Polymyxins probably also circulin and polypeptin (630)... 

Polymyxin Family (Polymyxin, Aerosporin, Circidin, Polypeptin)... 

Polypeptin (398) is also related to the polymyxins. It is isolated from cultures of a mutant of B. circulans, B. krzemieniewski, and is a basic heteromeric peptide, with an isoelectric point at 11.0 and containing a, y-diaminobutyric acid. Polypeptin is distinct from the polymyxins by, among other things, the presence of a chromogenic ultraviolet-absorbing group (290). 

Preparation and Properties of Polypeptin. The preparation of poly-peptin has been described by McLeod (398) and Howell (290). 

The fermentation medium (enriched with alanine) is inoculated with B. krzemieniew-ski. After 10 days, the culture is filtered and acetone and ammonium sulfate are added to the filtrate which is acidified to pH 2.0. The precipitated proteins are discarded, and the supernatant concentrated under vacuum. The concentrated extract is shaken with chloroform, and the polypeptin precipitates as a waxy mass, which is dissolved in hot aqueous acetone, and reprecipitated by cooling to —20 C. The polypeptin is then repurified by dissolving in hot aqueous ethanol, followed by its crystallization in the cold. Interesting photographs of the free polypeptin crystals and those of the sulfate are found in the publication of Howell (290). 

The crystalline form of the polypeptin sulfate depends to a large extent on the solvent used for its crystallization. The polypeptin sulfate is soluble at 25 C. to the extent of 5% in ethylene glycol, 8% in pyridine, 10% in glacial acetic acid, 4% in allyl alcohol, 12% in phenol. It dissolves rapidly in methanol to a concentration of 4%, and in ethanol to 5%, but precipitates some time after. It is insoluble in anhydrous acetone, ether, chloroform, amyl acetate, benzene, carbon disulfide, and petrol ether. Although slightly soluble in water itself, it is solubilized by sodium or ammonium acetate. 

The polypeptin sulfate melts with decomposition at 235. In 70% aqueous isopropyl alcohol solution, it is levorotatory [a] = —93 3 (c = 3%). It has characteristic absorption bands with maxima at 2520, 2580, and 2640 A the absorption coefficient is very high between 2000 and 2400 A, and becomes zero for wavelengths higher than 3000 A. 

Neither pepsin nor trypsin affects the biological activity of polypeptin sulfate. This activity is remarkably stable, even after treatment with certain chemical reactants. Polypeptin is not only an inhibitor of the growth of various lower fungi and bacteria, but also lyses red blood cells, and is toxic for mice (398). These antibiotic and inhibitory activities always go together (290). 

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