Effect of monolayer surface pressure on the activities of phosphoinositide-specific phospholipase C-beta 1, -gamma 1, and -delta 1.
Three isoforms of phospholipase C, either PLC-beta 1, PLC-gamma 1, or PLC-delta 1, were added to the aqueous subphase beneath phospholipid monolayers formed at an air-solution interface, and the initial rate of hydrolysis of phosphatidylinositol 4,5-bisphosphate was measured after addition of 10 microM free Ca2+. The monolayers were formed from mixtures of phosphatidylcholine (65% PC), phosphatidylserine (33% PS), and phosphatidylinositol 4,5-biphosphate (2% PIP2). Increasing the surface pressure of the monolayer, pi, from 15 to 25 mN/m decreases the rate of hydrolysis 16-, 13-, and 5-fold for PLC-beta 1, PLC-gamma 1, and PLC-delta 1, respectively. The simplest interpretation of these results is that a portion of each of the enzymes of area Ap must insert into the monolayer, doing work pi Ap, prior to hydrolysis of PIP2; binding studies with simple model compounds of known cross-sectional area are consistent with this interpretation. Removing the monovalent acidic lipid PS from the monolayer decreases the initial rates of hydrolysis of PIP2 about 3-fold for each PLC isoform, which suggests that negative electrostatic surface potentials increase the PLC activity.
Boguslavsky
V
V
Health Sciences Center, State University of New York, Stony Brook, New York 11794-8661.
Rebecchi
M
M
Morris
A J
AJ
Jhon
D Y
DY
Rhee
S G
SG
McLaughlin
S
S
D000818:Animals; D001921:Brain / Q000201:enzymology; D002417:Cattle; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes; D010713:Phosphatidylcholines / Q000494:pharmacology; D019269:Phosphatidylinositol 4,5-Diphosphate; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D018129:Phosphatidylinositol Phosphates / Q000494:pharmacology; D010718:Phosphatidylserines / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D011312:Pressure; D013499:Surface Properties
D007527:Isoenzymes; D008081:Liposomes; D010713:Phosphatidylcholines; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010718:Phosphatidylserines; D010727:Phosphoric Diester Hydrolases; D043265:Phosphatidylinositol Diacylglycerol-Lyase