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Characterization and Localization of Phospholipase A 2 Activity in Sympathetic Ganglia
Author(s) -
Quik M.
Publication year - 1987
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1987.tb13150.x
Subject(s) - phosphocholine , enzyme , phospholipase a , enzyme assay , phospholipase c , chemistry , phosphatidylcholine , egta , biochemistry , substrate (aquarium) , phospholipase , phospholipase a2 , medicine , endocrinology , biology , calcium , phospholipid , membrane , ecology , organic chemistry
Superior cervical ganglion phospholipase A 2 activity was characterized using l‐palmitoyl‐2‐[l‐ 14 C]arachidonoyl‐ sn ‐glycero‐3‐phosphocholine as a substrate. The enzyme activity exhibited linearity with interval of incubation and tissue concentration; there appeared to be two pH optima of the enzyme, at pH 6.0 and 9.0. A Lineweaver‐Burk plot of the reciprocal of activity versus substrate concentration yielded an apparent K m of 0.53 m M and a V max of 5.3 nmol/h/mg of protein. The enzyme exhibited a partial Ca 2+ dependence; in the absence of Ca 2+ and presence of EGTA, activity was reduced by 40%. The phospholipase A 2 activity was heat sensitive and was completely inactivated after treatment at 100°C for 30 min. For determination of whether the enzyme had a preference for hydrolysis of specific fatty acid substituents in the 2 position of phosphatidylcholine, several different substrates were tested. The order of preference for hydrolysis by the ganglionic enzyme was l‐palmitoyl‐2‐[l‐ 14 C]arachidonoyl‐ sn ‐glycero‐3‐phosphocholine = l‐palmitoyl‐2‐[1‐ 14 C]linoleoyl‐ sn ‐glycero‐3‐phosphocholine > l‐palmitoyl‐2‐[l‐ 14 C]palmitoyl‐ sn ‐gly‐cero‐3‐phosphocholine. For determination of the localization of the phospholipase A 2 enzyme in sympathetic ganglia, two approaches were used. Guanethidine, which results in destruction of adrenergic cell bodies in sympathetic ganglia, was administered to rats; an ˜50% decline in phospholipase A 2 activity was observed after this treatment. In other experiments, the preganglionic nerve to the ganglion was sectioned in rats; after 2 weeks of denervation, no significant change in ganglionic phospholipase A 2 activity was seen, although after 4 weeks of denervation, a small but non‐significant decrease in enzyme activity was observed. These results suggest that the enzyme has a predominantly post‐synaptic localization. Extrinsic phospholipase A 2 enzymes have previously been shown to affect postsynaptic function in rat sympathetic ganglia. The presence of a phospholipase A 2 in the tissue itself could suggest that endogenous phospholipase A 2 enzymes can regulate postsynaptic neuronal function.