title: Ca(2+)-independent phospholipase A2 activity associated with secretory granular membranes in rat parotid gland.
abstract: Phospholipase A2 activity was detected in a secretory granular fraction (SG) purified by Percoll gradient centrifugation from rat parotid gland using [3H]phosphatidylcholine (PC) as a substrate. High activity of this enzyme was observed at neutral pH. The enzyme was activated by Triton X-100 and did not require Ca2+ for its activity. In the absence of Ca2+, its apparent Km for exogenous PC was 28 microM while it was slightly increased by adding 5 mM CaCl2 (73 microM). Furthermore, the enzyme was located essentially in a granular membrane fraction separated from granular lysate. The deacylation activities were also detected in other subcellular fractions, which showed a different detergent-susceptibility or pH-dependency from that in SG. These results suggest that secretory granules have membrane-bound phospholipase A2 which has properties different from that found in other organelles.
authors.affiliation: Department of Oral Biochemistry, Asahi University School of Dentistry, Gifu, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Mizuno
authors.forename: Y
authors.initials: Y
authors.lastname: Kameyama
authors.forename: Y
authors.initials: Y
authors.lastname: Yokota
mesh_terms: D000215:Acylation / Q000187:drug effects; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D003594:Cytoplasmic Granules / Q000201:enzymology; D007425:Intracellular Membranes / Q000201:enzymology; D008297:Male; D017830:Octoxynol; D010306:Parotid Gland / Q000187:drug effects / Q000201:enzymology*; D010713:Phosphatidylcholines / Q000378:metabolism; D010741:Phospholipases A / Q000737:chemistry / Q000378:metabolism*; D054467:Phospholipases A2; D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000201:enzymology
chemical_list: D001095:Arachidonic Acids; D010713:Phosphatidylcholines; D016718:Arachidonic Acid; D011092:Polyethylene Glycols; D017830:Octoxynol; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium