1,2-Dipalmitoyl-3-β-2-furylacryloyltriacylglycerol: a chromophoric substrate for lipoprotein lipase

We have investigated the suitability of 1,2-dipalmitoyl-3-β-2-furylacryloyltriacylglycerol as a chromophoric substrate for lipoprotein lipase from Pseudomonas fragi. Steady-state kinetic experiments of the hydrolysis of emulsions of the ester chromophore catalyzed by lipoprotein lipase indicate that the Michaelis constant (K_m) has the same value throughout the pH range 7 to 9.5. The value of K_m was determined to be 0.1 mM from appropriate reciprocal plots; this K_m value is comparable to that for emulsions of other triacylglycerol substrates. Studies of the rate of hydrolysis, V_max, at different pH values indicate that the reaction is faster at basic pH, suggesting base catalysis of hydrolysis. A coupled assay for glycerol formed in the hydrolysis reaction catalyzed by lipoprotein lipase suggests that the rate of hydrolysis of the furylacryloyl side chain is faster than the rate of hydrolysis of the palmitoyl side chain at position 2, indicating that the chromophoric substrate is sufficiently reactive so that the usual stereochemical preference for hydrolysis at the 3 position is preserved. When mixed liposomes of phosphatidylcholine and chromophoric substrate are incubated with lipoprotein lipase there is an initial breakdown of the liposomes with release of chromophore into solution followed by a slow hydrolysis of chromophore; this result shows that the chromophoric substrate can be useful to monitor physical changes that occur in liposomes during the hydrolysis reaction catalyzed by lipoprotein lipase.