Identification of a putative surfactant convertase in rat lung as a secreted serine carboxylesterase.
In the alveolar lumen, pulmonary surfactant converts from the contents of secreted lamellar bodies to tubular myelin to apoprotein-depleted vesicles during respiration. Using an in vitro system, researchers have reported that the conversion of tubular myelin to vesicles is blocked by inhibitors of serine hydrolase activity and have tentatively ascribed "convertase" activity to a diisopropyl fluorophosphate (DFP)-binding protein in mouse bronchoalveolar lavage (BAL). We purified and sequenced the homologous enzyme from rat BAL fluid. Amino acid sequence from the amino terminus and an internal cyanogen bromide peptide of the purified rat DFP-binding protein perfectly match the sequence of the carboxylesterase ES-2. Although ES-2 was initially cloned from liver, we found a 1.8-kilobase mRNA for ES-2 in decreasing relative abundance in rat liver, kidney, and lung but not in heart or spleen. Although further studies are required to establish the identity between "convertase" and ES-2 or a homologous member of the carboxylesterase family, our results raise the possibility that a protein with esterase/lipase activity plays a role in extracellular surfactant metabolism.
Barr
F
F
Department of Pediatrics, University of California, San Francisco 94143-0130, USA.
Clark
H
H
Hawgood
S
S
D000595:Amino Acid Sequence; D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D043182:Carboxylesterase; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D018076:DNA, Complementary / Q000737:chemistry; D004791:Enzyme Inhibitors; D007531:Isoflurophate / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D008168:Lung / Q000201:enzymology*; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011663:Pulmonary Surfactants / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012697:Serine Endopeptidases / Q000378:metabolism
D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D011663:Pulmonary Surfactants; D007531:Isoflurophate; D002265:Carboxylic Ester Hydrolases; D043182:Carboxylesterase; D012697:Serine Endopeptidases; C068328:surfactant subtype convertase