A specific human lysophospholipase: cDNA cloning, tissue distribution and kinetic characterization

Lysophospholipases are critical enzymes that act on biological membranes to regulate the multifunctional lysophospholipids; increased levels of lysoph ospholipids are associated with a host of diseases. Herein we report the cD NA cloning of a human brain 25 kDa lysophospholipid-specific lysophospholip ase (hLysoPLA). The enzyme (at both mRNA and protein levels) is widely dist ributed in tissues, but with quite different abundances. The hLysoPLA hydro lyzes lysophosphatidylcholine in both monomeric and micellar forms, and exh ibits apparent cooperativity and surface dilution kinetics, but not interfa cial activation. Detailed kinetic analysis indicates that the hLysoPLA bind s first to the micellar surface and then to the substrate presented on the surface. The kinetic parameters associated with this surface dilution kinet ic model are resorted, and it is concluded that hLysoPLA has a single subst rate binding site and a surface recognition site. The apparent cooperativit y observed is likely due to the change of substrate presentation. In contra st to many non-specific lipolytic enzymes that exhibit lysophospholipase ac tivity, hLysoPLA hydrolyzes only lysophospholipids and has no other signifi cant enzymatic activity. Of special interest, hLysoPLA does not act on plas menylcholine. Of the several inhibitors tested, only methyl arachidonyl flu orophosphonate (MAFP) potently and irreversibly inhibits the enzymatic acti vity. The inhibition by MAFP is consistent with the catalytic mechanism pro posed for the enzyme-a serine hydrolase with a catalytic triad composed of Ser-119, Asp-174 and His-208. (C) 1999 Elsevier Science B.V. All rights res erved.