The mouse plasma PAF acetylhydrolase: I. Characterization and properties.
Mouse plasma platelet-activating factor acetylhydrolase (PAF-AH) has an apparent Km of 7.4 microM and a Vmax of 21.6 nmol/min per mg protein. Comparison with values reported for the human and the rat enzymes shows at least a 5-fold higher Vmax and similar enzyme-substrate affinity. Although lecithin:cholesterol acyltransferase (LCAT) and one component of the PAF-AH share similar masses and lipoprotein association, they are distinct enzymes. Similarly, PAF-AH is distinct from the phospholipase A2 (PLA2) and the lysophospholipase of mouse plasma. A series of PAF structural analogs showed either competitive inhibition or a mixed type of inhibition of PAF-AH. Mouse plasma PAF-AH is highly sensitive to 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) and is activated by deoxycholate. SDS-PAGE showed that two distinct proteins with molecular masses of 46 and 63 kDa contribute to the PAF-AH activity. The HDL-VHDL lipoprotein associated PAF-AH is precipitated to an extent of about 60% by phosphotungstate-MgCl2 and Tween 20 only partially solubilises the precipitated enzyme under conditions which can precipitate and solubilise the human enzyme.
Tsaoussis
V
V
Institute of Biology, National Centre for Scientific Research Demokritos, Aghia Paraskevi Attikis, Greece.
Vakirtzi-Lemonias
C
C
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D000818:Animals; D006868:Hydrolysis; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium; D051379:Mice; D008970:Molecular Weight; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000097:blood* / Q000302:isolation & purification; D054467:Phospholipases A2; D010772:Phosphotungstic Acid; D010972:Platelet Activating Factor / Q000378:metabolism; D013379:Substrate Specificity
D046911:Macromolecular Substances; D010972:Platelet Activating Factor; D010772:Phosphotungstic Acid; D010741:Phospholipases A; D054467:Phospholipases A2; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D008274:Magnesium