Interaction with bovine serum albumin of an anti-oxidative pectic arabinogalactan from Andrographis paniculata

A pectic arabinogalactan was obtained from the leaves of Andrographis paniculata by aqueous extraction followed by α-amylase treatment, deproteination, and anion exchange chromatography. Methylation analysis, Smith degradation, and NMR spectroscopy indicated that it was a highly branched arabinogalactan containing a (1 → 3)-linked β-d-Galp main chain, substituted at O-6 by (1 → 6)-linked β-d-Galp side chains. The latter residues were substituted at O-3 by (1 → 5)- and (1 → 3)-linked α-l-Araf chains, and non reducing end-units of α-l-Araf and β-d-Galp. This homogeneous arabinogalactan (36 kDa), which contained phenolic acids, showed dose-dependent anti-oxidative properties. The phenolic acid moieties might be the functional sites. This arabinogalactan can form a complex with bovine serum albumin having binding constant K = 6.48 × 106/M. Thus, this study is an important step forward to investigate the involvement of arabinogalactan in processes including interaction with biologically important transport proteins.