Department of Animal Toxinology, Kunming Institute of Zoology, the Chinese Academy of Sciences, Kunming, Yunnan 650223, China 2. Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
Frog albumin (XpA-serum) was purified from serum of Xenopus laevis by a combination of gel filtration and ion exchange chromatography steps. Like Bombina maxima albumin, XpA-serum exhibited trypsin inhibitory activity, which was lower than that of B. maxima albumin. XpA-serum at the concentration of 180 nM inhibited 84% activity of trypsin (30 nM). The equilibrium dissociation constants (KD) is 1.44×10-6 M as determined by Surface Plasmon Resonance. Western blot analysis revealed that XpA-serum was also distributed in the skin. It is deduced that serum albumin of amphibian possessing trypsin inhibitory activity can function directly or indirectly as a defensive substance against predators.