STRUCTURAL STUDIES OF PULLULAN BY NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

Nuclear Magnetic Resonance (NMR) spectroscopy was used to probe the pr imary structure of the glucan pullulan. Carbon-13 proton and phosphoru s-31 NMR spectra in aqueous solution of the intact polysaccharide obta ined from three different sources indicate that significant structural differences can occur among these samples. In particular, two samples consist solely of alpha(1-->6) linked maltotriose units, in accord wi th the generally accepted structure. However a third sample has fewer alpha(1-->6) linkages and appeals to consist of higher alpha(1-->6) li nked maltooligosaccharides in addition to maltotriose. Unlike the othe r samples, this sample was also phosphorylated. Enzymatic digestion of pullulan followed by NMR spectroscopy using pullulanase confirmed the se results, as did HPLC analysis of the resulting digest, which showed the presence of maltooligosaccharides consisting of ten and more gluc ose units. However, HPLC analysis of acid hydrolysed pullulan indicate d that no sugars other than glucose were present in any of the samples examined.