Purification and properties of phospholipases A2 from the crown-of-thorns starfish (Acanthaster planci) venom.

Two phospholipases A < inf2 (named AP-PLA2-I and II) were purified from the crown-of-thorns starfish (Acanthaster planci) venom. Both enzymes were confirmed to be PLA2s, based on the results that they showed hemolytic activity only in the presence of phosphatidylcholine (PC) and also released fluorescent fatty acids from PC with labeled fatty acids at the sn-2 position. The enzyme activity of both PLA2s was enhanced by Ca2+ but reduced by Cu2+ and Zn2+. The molecular mass of AP-PLA2-I was estimated to be 28 kDa by gel filtration and 15 kDa by SDS-PAGE, indicating that AP-PLA2-I is a dimer composed of the same subunit. In contrast, AP-PLA2-II was judged to be a monomer with a molecular mass of 12 kDa (gel filtration) or 15 kDa (SDS-PAGE). The amino acid compositions of the two enzymes were comparable to each other; Asx, Glx and Gly were rich in both molecules, while Met, His and Trp were poor. Analyses by a sequencer determined the first 62 amino acid residues for both PLA2s. In the AP-PLA2-I preparation, minor amino acids were additionally found at 17 positions, suggesting the coexistence of another PLA2-component. As compared to the N-terminal sequences of the known PLA2s, both AP-PLA2-I and II were identified as class I enzymes not only because they have Cys-11 and lack Cys-51 but also because they contain the elapid loop in the region 53-61.