Abstract:

To fully understand the proliferation of splenocyte in vitro of natto ingredients, two kinds of polysaccharideprotein
complexes, named as NPPC-1-b and NPPC-2-a, were extracted and purified from natto by DEAE-52 cellulose ionexchange
chromatography and Sephadex G-100 gel filtration chromatography. Their molecular weights were determined
by performance gel permeation chromatography to be approximately 26.93 and 357.60 kD for NPPC-1-b and NPPC-2-a,
respectively. The two complexes were further characterized by FT-IR, UV-visible spectrophotometry, monosaccharide
and amino acid composition analysis. The results showed that NPPC-1-b contained an O-glycopeptide bond, while
NPPC-2-a contained an N-glycopeptide bond. NPPC-1-b was mainly composed of mannose (Man), rhamnose (Rha)
and arabinose (Ara), with the contents of 67.45%, 25.67% and 2.44%, respectively. However, NPPC-2-a was mainly
composed of glucose (Glc), mannose (Man), arabinose (Ara), xylose (Xyl) and galactose (Gal), accounting for 36.64%,
21.71%, 10.35%, 9.00% and 5.17%, respectively. Seventeen amino acids were identified in both complexes. NPPC-1-b
was mainly composed of glutamic (Glu), proline (Pro), lysine (Lys) and arginine (Arg) with contents of 0.971%, 0.791%,
0.708% and 0.603%, while NPPC-2-a was mainly composed of Glu, Pro and aspartic (Asp) acid with contents of 0.903%,
0.689% and 0.504%. Besides, preliminary in vitro tests showed that NPPC-1-b (100–200 μg/mL) and NPPC-2-a (12.5–
200 μg/mL) exhibited significantly higher immunomodulatory activities against the proliferation of lymphocytes
(P < 0.05), and the effect of 100 μg/mL NPPC-2-a was the best. In respect of cytokines expression, NPPC-1-b and NPPC-2-a
significantly enhanced the expression of interleukin-2 (IL-2) and interferon-γ (INF-γ), and 50 μg/mL NPPC-1-b showed a
strong effect on IL-2 secretion, 200 μg/mL NPPC-2-a exhibited a strong effect on INF-γ secretion. These results suggest that
NPPC-1-b and NPPC-2-a can effectively increase immunomodulatory activity.

Key words: natto, polysaccharide-protein complexes, structure analysis, immunomodulatory activity