Functional characteristics of a phospholipase A2 inhibitor from Notechis ater serum

Abstract

A phospholipase A2 inhibitor has been purified from the serum of Notechis ater using DEAE-Sephacel chromatography. The inhibitor was found to be composed of two protein subunits (α and β) that form the intact complex of approximately 110 kDa. The α-chain is a 30-kDa glycoprotein and the β- chain a nonglycosylated, 25-kDa protein. N-terminal sequence analysis reveals a high level of homology to other snake phospholipase A2 inhibitors. The inhibitor was shown to be extremely pH and temperature stable. The inhibitor was tested against a wide variety of phospholipase A2 enzymes and inhibited the enzymatic activity of all phospholipase A2 enzymes tested, binding with micromole to nanomole affinity. Furthermore, the inhibitor was compared with the Eli-Lilly compound LY311727 and found to have a higher affinity for human secretory nonpancreatic phospholipase A2 than this chemical inhibitor. The role of the carbohydrate moiety was investigated and found not to affect the in vitro function of the inhibitor.