Ed. Bent et Jd. Bell, QUANTIFICATION OF THE INTERACTIONS AMONG FATTY-ACID, LYSOPHOSPHATIDYLCHOLINE, CALCIUM, DIMYRISTOYLPHOSPHATIDYLCHOLINE VESICLES, AND PHOSPHOLIPASE A(2), Biochimica et biophysica acta, L. Lipids and lipid metabolism, 1254(3), 1995, pp. 349-360
The rate of hydrolysis of phosphatidylcholine bilayers by soluble phos
pholipase A(2) (PLA(2)) is greatly enhanced by the presence in the bil
ayer of a threshold mole fraction of the reaction products: fatty acid
and lysophosphatidylcholine (lyse-PC). The threshold requirement of t
hese products appears to vary as a function of vesicle and calcium con
centration. To further identify the roles of myristic acid, lyse-PC, a
nd calcium in promoting optimal PLA(2) activity, we have quantified th
e various interactions among these components and dimyristoylphosphati
dylcholine large unilamellar vesicles. The bilayer/water partition coe
fficient for myristic acid was obtained by competition of vesicles for
the binding of the fatty acid to an acrylodan conjugate of an intesti
nal fatty acid binding protein as monitored by the acrylodan fluoresce
nce emission spectrum. The partition coefficient for lyse-PC was obtai
ned by a similar procedure using the tryptophan emission spectrum of b
ovine serum albumin. The effect of calcium concentration on these inte
ractions was also quantified. These results were incorporated into an
empirical model to describe the threshold requirements for these produ
cts in the bilayer. This information is vital for elucidating the mech
anism of activation of PLA, by the hydrolysis products.