CLONING, EXPRESSION AND CHARACTERIZATION OF PLASMA PLATELET-ACTIVATING FACTOR-ACETYLHYDROLASE FROM GUINEA-PIG

In a previous study, we purified PAF-acetylhydrolase, which converts P AF to an inactive metabolite, lysoPAF, from peritoneal fluid of guinea pigs subjected to experimental endotoxin shock and found that this pu rified enzyme had similar biochemical properties to the plasma enzyme [Karasawa, K., Yato, M., Setaka, M., and Nojima, S. (1994) J. Biochem. 116, 374-379]. In this study, we isolated a homogeneous enzyme prepar ation from guinea pig plasma using a similar procedure, The molecular mass of this purified enzyme, as determined by SDS-PAGE was 58-63 kDa, larger than that (43 kDa) of the human enzyme. To elucidate the molec ular structure of this enzyme and clarify its relationships with PAF-a cetylhydrolases of other species, we isolated and sequenced a cDNA enc oding this enzyme. Its cDNA contains an open reading frame encoding 43 6 amino acids and its predicted molecular mass (49 kDa) is lower than that of the native enzyme, suggesting that guinea pig plasma PAF-acety lhydrolase, unlike the human enzyme, is modified post-translationally, perhaps by glycosylation.