Recognition of acidic phospholipase A2 activity in plasma membranes of resident peritoneal macrophages
Phospholipase (PLase) activities in the plasma membrane of guinea pig peritoneal macrophages were studied, as these enzymes having such activity may be candidates for the release of arachidonic acid (AA) from phosphatidylcholine (PC). An AA release system operating at acidic pH was identified in the macrophage plasma membrane and characterized. This membrane-bound acidic PLase A/sub 2/ had an optimum pH at 4.5, and enzyme activation was observed in Ca/sup + +/-free medium; but the maximum activity was found at 0.5 mM Ca/sup + +/ concentration. The Km value for PC of acidic PLase A/sub 2/ was 4.2 ..mu..M, and a Michaelis-Menten relationship was evident. Calcium might act as a cofactor at some intermediate step during the activation of acidic PLase A/sub 2/ in light of the uncompetitive manner of Ca/sup + +/ action. Furthermore, the release of (/sup 3/H)-AA from preradiolabelled macrophage plasma membranes occurred with the addition of Ca/sup + +/ at pH 4.5. These data suggest that the acid PLase A/sub 2/ is a component of the plasma membrane and is not due to lysosomal contamination since membrane-bound acidic PLase A/sub 2/ properties are opposite to those found for lysosomal PLase A/sub 2/.
- Research Organization:
- Nihon Univ. School of Dentistry, Matsudo (Japan)
- OSTI ID:
- 6292606
- Journal Information:
- Life Sci.; (United States), Vol. 43:11
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ARACHIDONIC ACID
SECRETION
LIPASE
ENZYME ACTIVITY
CALCIUM COMPOUNDS
CATIONS
CELL MEMBRANES
GUINEA PIGS
LYSOSOMES
MACROPHAGES
PERITONEUM
PH VALUE
PHOSPHOLIPIDS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
ANIMAL CELLS
ANIMALS
CARBOXYLESTERASES
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHARGED PARTICLES
CONNECTIVE TISSUE CELLS
ENZYMES
ESTERASES
ESTERS
HYDROLASES
IONS
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
LIPIDS
MAMMALS
MEMBRANES
MONOCARBOXYLIC ACIDS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
ORGANOIDS
PHAGOCYTES
RODENTS
SEROUS MEMBRANES
SOMATIC CELLS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques