The hydrolysis of phosphatidylinositol monolayers at an air/water interface by the calcium-ion-dependent phosphatidylinositol phosphodiesterase of pig brain

Abstract

1. The activity of Ca2+-dependent phosphatidylinositol phosphodiesterase (EC 3.1.4.10) of pig brain against [32P]phosphatidylinositol monolayers at an air/water interface has been measured. As the monolayer pressure was increased a sharp cut-off of enzymic hydrolysis occurred at 33 X 10(-3) N/m. 2. The addition of either phosphatidic acid, phosphatidylglycerol or oleyl alcohol increased the film pressure at which cut off occurred, as well as increasing the rate of hydrolysis at lower pressures. 3. The rate of hydrolysis, but not the cut-off pressure, was markedly increased by oleic acid and slightly increased by phosphatidylethanolamine. 4. Phosphatidylcholine, palmitoylcholine and octadecylamine decreased the cut-off pressure, as well as the enzymic activity below this pressure. 5. Stearic acid and stearyl alcohol had no effect on either the cut-off pressure or the activity. 6. All activators decreased the length of the lag phase before enzyme activity began, and phosphatidylcholine increased it. 7. These results are compared with the stimulatory and inhibitory effects of various amphiphiles observed previously with phosphatidylinositol dispersions [Irvine, Hemington & Dawson (1979) Eur. J. Biochem. 99, 525-530], and their possible relevance to the control of the phosphatidylinositol phosphodiesterase in vivo are discussed.

Surface pressure‐dependent cross‐modulation of sphingomyelinase and phospholipase A2 in monolayers

“…Obviously, the specific critical values of the regulatory surface parameters (i.e., cut-off and optimal surface pressure points, composition-dependent lateral microheterogeneity, electrostatic surface potential) may certainly be expected to vary for different enzymes, including the physiologically relevant mammalian enzymes such as Group II or V secretory PLA s , the various forms of membrane or cytosolic PLA 2 (35) that might work in conjunction with membrane Sphmase. Except for both brain phosphatidylinositol phosphodiesterase (8) and more recently for phosphoinositide-specific phospholipase C (12,13) and phospholipase Cβ (14) for which surface pressure-dependent activity was shown, biophysical studies have not yet been performed with most membrane phospholipases.…”

“…This is an invaluable advantage for further exploring the new aspects described in this work on the complex factors regulating phosphohydrolytic surface catalysis. Moreover, all phosphohydrolytic enzymes studied so far in model systems have revealed very similar generic interfacial factors for their surface regulation (1)(2)(3)(4)(5)(6)(7)(8)(9)(12)(13)(14)(15). Obviously, the specific critical values of the regulatory surface parameters (i.e., cut-off and optimal surface pressure points, composition-dependent lateral microheterogeneity, electrostatic surface potential) may certainly be expected to vary for different enzymes, including the physiologically relevant mammalian enzymes such as Group II or V secretory PLA s , the various forms of membrane or cytosolic PLA 2 (35) that might work in conjunction with membrane Sphmase.…”

“…The unique possibility of lipid monolayers maintaining a control and precise knowledge of several surface parameters in real time during a catalytic reaction showed that, besides the influence of structural defects and curvature (3)(4)(5), the lateral surface pressure and electrostatic interfacial potential (6,7) can markedly affect the activity of phospholipase A 2 (PLA 2 ), phosphatidylinositol-specific and nonspecific phospholipase C, and sphingomyelinase (Sphmase) (8)(9)(10)(11)(12)(13)(14). Despite the fact that phosphohydrolytic enzymes constitute a very heterogeneous group of proteins, all activities studied to date have revealed a profound dependence on a few fundamental supramolecular surface parameters of the lipid interface on which they act (1)(2)(3)(4)(5)(6)(7)(8)(9)(13)(14)(15). This is extremely important because it means that biophysical studies in model systems, usually requiring relatively large amounts of well-purified enzymes and lipids, can provide valuable information using readily available secretory or bacterial phosphohydrolytic enzymes when the aim is, as in the present work, to understand the general basic physicochemical parameters regulating these activities.…”

“…Lipid monolayers in particular, the model on which the very concept of a lipid bilayer as the basic constitutive structure of biomembranes was derived, clearly demonstrated that the activity of several phospholipases from different sources is markedly affected by both the long-range physical state and the fine intermolecular organization of the lipid interface (1,2). The unique possibility of lipid monolayers maintaining a control and precise knowledge of several surface parameters in real time during a catalytic reaction showed that, besides the influence of structural defects and curvature (3-5), the lateral surface pressure and electrostatic interfacial potential (6,7) can markedly affect the activity of phospholipase A 2 (PLA 2 ), phosphatidylinositol-specific and nonspecific phospholipase C, and sphingomyelinase (Sphmase) (8)(9)(10)(11)(12)(13)(14). Despite the fact that phosphohydrolytic enzymes constitute a very heterogeneous group of proteins, all activities studied to date have revealed a profound dependence on a few fundamental supramolecular surface parameters of the lipid interface on which they act (1-9,13-15).…”

Localization of phospholipase C δ3 in the cell and regulation of its activity by phospholipids and calcium

“…The X-ray structure of PLC δ1 shows that the catalytic domain falls in the region of residues 299Ϫ606 [39]. In PLC δ3, the corresponding region stretches from positions 287 to 589. calcium-dependent phosphatidylinositol phosphodiesterase from pig brain [54].…”