Isolation and characterization of ACTX-6: a cytotoxic L-amino acid oxidase from Agkistrodon acutus snake venom

The characterization of an L-amino acid oxidase purified from Agkistrodon acutus snake venom was investigated. An L-amino acid oxidase (LAAO) was purified from A. acutus snake venom through DEAE Sepharose F.F. and Source 30 S chromatography. The molecular mass of this enzyme was determined by SDS-PAGE, size exclusion chromatography, and mass spectrometry. Substrate specificity, cytotoxicity, antitumor activity in vivo, and apoptosis-inducing activity were assayed. The LAAO purified from A. acutus snake venom was designated as ACTX-6. It is a covalently bound homodimer and its molecular mass is about 96 kDa. This enzyme preferred to oxidize hydrophobic L-amino acids; the best substrates were L-Met, L-Leu, L-Trp, and L-Phe. ACTX-6 demonstrated cytotoxicity in vitro and could inhibit tumor growth in vivo. Flow cytometry analysis showed that it could markedly increase accumulation of sub-G1 phase, which suggested that this enzyme could induce apoptosis. ACTX-6 could effectively inhibit tumor growth and it is a potential substance to develop into an antitumor drug.