Therapeutic polypeptide from yeast

The invention relates to a therapeutic polypeptide for increasing resistance to infections and stress and without substantial pyrogenic or antigenic action, recovered from yeast-cell wall material, being substantially free from polypeptides of molecular weight less than 1000, being heat stable at least up to 100 DEG C., being soluble in liquid phenol, in water and in aqueous bases, being precipitatable from aqueous solution by phosphotungstic acid and sulphosalicylic acid, showing a yellow-green fluorescence and containing the following amino acids in polypeptide form namely glutamic and aspartic acids, argimine, lysine, alanine serine, valine, leucine, isoleucine, glycine, phenylalanine histidine, proline, tyrosine and threobine, being substantially free from combined phosphorus exhibiting a positive anthrone and biuret reaction and having an antimitotic effect against He La and Chang cells. Preferably the polypeptide is free from polypeptides having a molecular weight less than 8000. It may be isolated from zymosan, a substantially protein-and carbohydrate-free water-insoluble yeast cell-wall product, by extraction with 90% aqueous phenol at 37 DEG C., followed by treatment of the extract with water-ether, separation of the water layer, addition of NH40H to solubilize any insolubles, treatment with ether to remove traces of phenol and freeze-drying. Alternatively, zymosan may be treated with NaOH for 24 hours, the supernatant separated and neutralized, concentrated and filtered. The solution was purified by fractionation or a Sephadex G50 column equilibrated with water-containing 0.3% cresol. Further purification may be by dialysis and ultrafiltration. The therapeutic polypeptide may be formulated into compositions for oral, parenteral, topical and rectal administration.