Phospholipase A 2 from Trypanosoma congolense : Characterization and haematological properties

Phospholipase A 2 was isolated from Trypanosoma congolense and purified to electrophoretic homogeneity. The enzyme appeared to exist in a dimeric form with subunit molecular weights of 16 500 and 18 000. It had a pH optimum of 6·8. Kinetic analysis with different substrates, showed that the enzyme had exceptional specificity for 1,2,dimyristoyl‐ sn ‐phosphatidylcholine and 1,2,dioleoyl‐ sn ‐phosphatidylcholine with K m values of 1·85 × 10 −3 M and 2·12 × 10 −3 M respectively. The Arrhenius plot was linear with an activation energy of 5·8 kcal mol −1 . Inhibition studies with parahydroxymercuribenzoate and tri‐butyltinoxide were positive thus implicating a thiol group at the catalytic site of the enzyme. The enzyme was stable to heat treatment and possessed haemolytic and anticoagulating properties.