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Abstract
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.