In vitro production of specific polysaccharides: isolation and structure of an antitumor active β-glucan from Phytophthora parasitica

Abstract

Polysaccharides are known to be an important group of biological polymers which are of great interest for industrial use. Besides their physical properties, their chemical structures can be the base for specific applications in medicine. Various polysaccharides are known to exhibit an antitumor activity, which is thought to be host mediated by a stimulation of the host's immune system. A β-1.3/1.6-glucan P isolated from the cell walls of Phytophthora parasitica Dastur (Mating type A1, 1828) exhibited strong antitumor activity against Sarcoma-180 in mice. Growth of the fungus was markedly stimulated by β-sitosterol and calcium ions. The fungus was shown to be thiamine heterotroph. At optimal growth conditions up to 30 g (dry weight) of fungal mycelium could be harvested within 5 days in 81 of culture medium, which represented ~6 g of cell wall material. A specific water-soluble cell wall glucan P was isolated by extraction with hot water and purification by ion-exchange and Con A chromatography. By methylation analysis it was shown that the β-glucan consisted of 1.3-, 1.3.6- and terminal-glucose residues in a molar ratio of 5:1:1. Sequential Smith degradations combined with methylation analyses showed the presence of mono- as well as di- and trisaccharides as side chain constituents in a ratio of 9:2:3. A structure of the antitumor active β-1.3/1.6-glucan P is proposed.