title: The contribution of individual lipoproteins to the degradation of platelet-activating factor in human serum.
abstract: Platelet-activating factor (PAF) is rapidly degraded in vivo by the action of a specific acetylhydrolase. Measuring the PAF-acetylhydrolase activity in serum from 12 healthy volunteers a maximum velocity of 67.2 +/- 11.8 nmol/min X ml and a Km value of 15.8 +/- 2.9 mumol/l were ascertained. More than 90% of the activity was found to be associated with lipoproteins. It was detected in isolated VLDL, LDL, Lp(a) as well as HDL2 but not in HDL3. The PAF-acetylhydrolase activities associated with the various lipoproteins were shown to behave like a unique enzyme with distinct kinetic properties. Because VLDL and LDL were found to take up about 5 and 2.5 times more PAF with respect to their mass than HDL, it is concluded that lipoproteins affect the PAF-acetylhydrolase activity at the level of substrate presentation. As a consequence of the distinct kinetic properties, the lipoprotein-associated PAF-acetylhydrolase activities do not contribute proportionately to the degradation of PAF in serum. The latter is shown to depend primarily on the amount of PAF-acetylhydrolase bound to the apoprotein B-containing lipoproteins.
authors.affiliation: Institute of Pathological Biochemistry, Medical Academy of Erfurt, GDR.
authors.forename: G
authors.initials: G
authors.lastname: Ostermann
authors.forename: G M
authors.initials: GM
authors.lastname: Kostner
authors.forename: A
authors.initials: A
authors.lastname: Gries
authors.forename: E
authors.initials: E
authors.lastname: Malle
authors.forename: U
authors.initials: U
authors.lastname: Till
mesh_terms: D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D006801:Humans; D006868:Hydrolysis; D008074:Lipoproteins / Q000302:isolation & purification / Q000502:physiology*; D010741:Phospholipases A / Q000097:blood; D010972:Platelet Activating Factor / Q000378:metabolism* / Q000502:physiology; D012709:Serum Albumin / Q000378:metabolism
chemical_list: D008074:Lipoproteins; D010972:Platelet Activating Factor; D012709:Serum Albumin; D010741:Phospholipases A; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase