We investigated whether Al3+-mediated changes in membrane fluidity can affect the activity of prokaryotic enzymes phospholipase C (PLC) and phospholipase C-phosphatidyl inositol specific (PI-PLC) in liposomes of phosphatidyl choline (PC), PC:phosphatidyl inositol (PI), or PC and polyphosphoinositides (PPI). Al3+ (10-100 μM) promoted membrane rigidification, evaluated with the probes 1,6-diphenyl-1,3,5-hexatriene and Laurdan, and followed the order: PC:PPI>PC:PI>PC. Al3+ (25 and 50 μM) did not affect PLC-mediated hydrolysis of PC, PI and PIP2, but stimulated PIP hydrolysis (48.6%). PI-PLC did not affect PC, PI, and PIP concentrations, but caused a 67% decrease in PIP2. Al3+ significantly inhibited PIP2 hydrolysis in a concentration-dependent (25-50 μM) manner. Results suggest that the inhibition of PIP2 hydrolysis by Al3+ could be partially due to a higher lipid packing induced by Al3+ which could affect the interaction between the enzyme and its substrate.
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