Inhibition of Trimeresurus flavoviridis phospholipase A2 by lung surfactant protein A (SP-A).
A marked sequence homology has been noted between lung surfactant protein A (SP-A) and an inhibitor of phospholipase A2 (PLA2) isolated from the serum of Trimeresurus flavoviridis (Habu snake). This study evaluated the effect of SP-A on PLA2 activity from several sources. SP-A was isolated from bovine or rat lung surfactant by extraction with 1-butanol and octyl beta-D-glucopyranoside. The addition of SP-A produced a concentration-dependent inhibition of T. flavoviridis PLA2 that indicated non-competitive kinetics with Ki 5 micrograms/ml. Inhibition was reversed by heat inactivation, disulfide bond reduction or alkylation of SP-A, or by the presence of anti-SP-A antibody. Treatment of SP-A with endoglycosidase F or the presence of variation monosaccharides or lectins did not alter SP-A inhibition. Binding of PLA2 to SP-A was shown by ultrafiltration and was abolished by SP-A alkylation or the presence of SDS. The SP-A/PLA2 complex recovered from the ultrafilter had essentially no enzymatic activity, but activity was restored by treatment with mercaptoethanol. SP-A had no effect on activity of PLA2 from Naja naja, Crotalus atrox, or bovine pancreas. These results indicate that surfactant protein A selectively inhibits Trimeresurus phospholipase A2 activity and suggest that binding to the enzyme is the mechanism for inhibition.
Fisher
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Institute for Environmental Medicine, University of Pennsylvania Medical Center, Philadelphia 19104-6068.
Dodia
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Chander
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Beers
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Bates
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D000818:Animals; D002417:Cattle; D003435:Crotalid Venoms / Q000037:antagonists & inhibitors; D008297:Male; D008970:Molecular Weight; D010741:Phospholipases A / Q000037:antagonists & inhibitors*; D054467:Phospholipases A2; D011510:Proteolipids / Q000737:chemistry / Q000494:pharmacology*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017841:Trimeresurus
D003435:Crotalid Venoms; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D010741:Phospholipases A; D054467:Phospholipases A2