LUNG SURFACTANT CONVERTASE IS A MEMBER OF THE CARBOXYLESTERASE FAMILY

The extracellular conversion of lung surfactant from tubular myelin to the small vesicular form has previously been shown to require a serin e-active enzyme called ''surfactant convertase.'' In the present study , a 72kD serine-active enzyme previously identified in mouse lung alve olar lavage and having convertase activity was partially sequenced. Si xty-eight residues obtained from amino acid sequencing of this protein show that it is a new member of the mouse carboxylesterase family (EC 3.1.1.1). The 72kD lung protein also has esterase activity. A commerc ial esterase of the same family was able to reproduce surfactant conve rtase bioactivity in vitro, unlike several serine proteinases previous ly tested. We conclude that surfactant convertase is a carboxylesteras e which mediates a biochemical step in the extracellular metabolism of surfactant. (C) 1997 Academic Press.