NEUTRAL EXTRACELLULAR GLUCAN OF PULLULARIA PULLULANS (DE BARY) BERKHOUT

Abstract

A neutral extracellular glucan ([α]D²³ + 189°) was produced in 12% yield by Pullularia pullulans (de Bary) Berkhout grown on a glucose substrate. A single symmetrical peak on free-boundary electrophoresis in borate and acetate buffers was evidence of homogeneity. Infrared spectroscopy showed that the predominant glucoside linkages were α(1 → 4) and α(1 → 6) with a small proportion of α(1 → 3). Graded acid hydrolysis under conditions of minimum reversion yields glucose, maltose, isomaltose, nigerose, panose, and isomaltotriose. In addition, a trisaccharide, O-α-D-glucopyranosyl-(1 → 4)-O-α-D-glucopyranosyl-(1 → 6)-D-glucopyranose, was isolated. Another trisaccharide was isolated and tentatively identified as O-α-D-glucopyranosyl-(1 → 4)-O-[α-D-glucopyranosyl-(1 → 6)]-D-glucose and hence a small degree of branching may occur in the molecule. The present study has confirmed previous observations that the main linkages are α(1 → 4) and α (1 → 6) and has provided unequivocal proof of the presence of α (1 → 3) linkages. Periodate oxidation studies confirmed the foregoing structural features and showed that the glucan was linked α(1 → 4), 65%; α(1 → 6), 29%; and α(1 → 3), 6%.