scholarly journals THE EFFECT OF AMPHIPHILIC LIQUID CRYSTALLINE SOLVENTS ON THE HYDROLYSIS OF BENZYLIDENE t-BUTYLAMINE N-OXIDE

1979 ◽  
Vol 40 (C3) ◽  
pp. C3-438-C3-441
Author(s):  
W. E. BACON ◽  
J. W. THOMAS
Keyword(s):  
Liquid Crystalline ◽  
Hydrolysis Of

Delayed cotyledon senescence following treatment with a cytokinin; an effect at the level of membranes

1980 ◽  
Vol 58 (16) ◽  
pp. 1797-1803 ◽  
Author(s):  
M. L. Gilbert ◽  
J. E. Thompson ◽  
E. B. Dumbroff
Keyword(s):  
Weight Loss ◽  
Phaseolus Vulgaris ◽  
Liquid Crystalline ◽  
Seedling Development ◽  
Hydrolysis Products ◽  
Microsomal Membranes ◽  
Gel Phase ◽  
Storage Cells ◽  
Hydrolysis Of ◽  
Cotyledon Senescence

Application of 10−4 M benzyladenine to Phaseolus vulgaris germinated under etiolating conditions markedly delayed the onset of cotyledon senescence. Weight loss was curtailed, hydrolysis of starch and protein reserves was delayed, and the rate at which hydrolysis products were translocated out of the cotyledons was reduced in treated plants. Microsomal membranes of cotyledons from control seedlings acquired increasing proportions of gel phase lipid as senescence of the tissue intensified. The resulting mixture of liquid-crystalline and gel phase lipid within the membrane matrix renders the membranes leaky and may partially contribute to metabolite translocation out of the cotyledon storage cells during seedling development. This prospect is supported by the observation that in benzyladenine-treated plants the onset of gel phase lipid, and hence of membrane leakiness, was delayed in a manner that corresponded temporally with the decreased rate of metabolite translocation out of the cotyledons.

Heterogeneous catalysis by phospholipase A2: formulation of a kinetic description of surface effects

1979 ◽  
Vol 57 (1) ◽  
pp. 97-106 ◽  
Author(s):  
David O. Tinker ◽  
Jane Wei
Keyword(s):  
Fatty Acid ◽  
Crystalline Phase ◽  
Liquid Crystalline ◽  
Surface Effects ◽  
Liquid Crystalline Phase ◽  
Desorption Rate ◽  
Substrate Complex ◽  
Steady State Kinetics ◽  
Mechanism Of Catalysis ◽  
Hydrolysis Of

The kinetics of hydrolysis of aqueous dispersions of long-chain, saturated phosphatidylcholines (PC) catalysed by Crotalus atrox phospholipase A2 (PLA) have been analysed, and a reaction mechanism proposed which takes surface effects into account. PLA is proposed to form an enzyme–substrate complex with surface substrate molecules, thereby undergoing a conformational change which exposes sites that interact with the lipid surface. After a hydrolytic event, the enzyme can either desorb from the surface (path 1), or diffuse along the surface to an adjacent substrate molecule (path 2). The path 1 dominated mechanism leads to Michaelis–Menten steady-state kinetics, and characterizes hydrolysis of gel phase PC. Evidence for saturation of the surface with PLA was obtained at high enzyme concentrations. The path 2 mechanism dominates when the desorption rate is very small; this mechanism describes hydrolysis of liquid crystalline phase PC and is characterized by an initial burst of hydrolysis followed by a very slow reaction. The velocities in these two phases of the reaction are independent of bulk PC concentration. When gel and liquid crystalline PC phases coexist, as in mixtures of dimyristoyl- and distearoyl-PC, the liquid crystalline phase is preferentially hydrolysed. Products of the reaction (lyso-PC and fatty acid) stimulate hydrolysis, apparently by stimulating desorption of PLA. The desorption rate constant appears to be a linear function of the surface concentrations of lyso-PC and fatty acid. The proposed model describes hydrolysis progress curves extremely well and is consistent with current ideas on the mechanism of catalysis by this enzyme.

Kinetics of hydrolysis of dispersions of saturated phosphatidylcholines by Crotalus atrox phospholipase A2

1978 ◽  
Vol 56 (6) ◽  
pp. 552-558 ◽  
Author(s):  
David O. Tinker ◽  
A. David Purdon ◽  
Jane Wei ◽  
Eileen Mason
Keyword(s):  
Liquid Crystalline ◽  
Phase Reaction ◽  
Reaction Products ◽  
Crotalus Atrox ◽  
Dipalmitoyl Phosphatidylcholine ◽  
Desorption Rate Constant ◽  
Rate Of Hydrolysis ◽  
Lag Period ◽  
Lipid Surface ◽  
Hydrolysis Of

Dispersions of lamellar phase dipalmitoyl phosphatidylcholine (DDPC) and dimyristoyl phosphatidylcholine (DMPC) in 0.01 M CaCl2 were subjected to hydrolysis by phospholipase A2 (EC 3.1.1.4) from Crotalus atrox venom. The reaction was followed continuously by titrating the released fatty acids. For hydrolysis of gel phase phosphatides, the steady-state initial velocities were hyperbolic functions of bulk lipid concentrations. At the 'pre-transition' temperature (34 °C for DPPC, 15 °C for DMPC), there was a large increase in the Michaelis parameter Vmax but no change in the parameter Km. A model was devised to account for these observations, in which the enzyme desorbs from the lipid surface after hydrolysis. The desorption rate constant is postulated to increase above the pretransition temperature.For hydrolysis of liquid crystalline phosphatides, the reaction consisted of a short initial burst of hydrolysis, a long 'lag' period of very slow reaction, followed by a dramatic increase in the reaction rate. Addition of 10 mol% lysolecithin or fatty acid abolished the 'lag' period. It was postulated that the enzyme adsorbs irreversibly to the surface of the liquid crystalline phase. Reaction products are postulated to stimulate desorption of enzyme from the surface. Thus, temperature-dependent changes in the rate of hydrolysis of dispersed phosphatidylcholines are attributed to changes in the rate of desorption of the enzyme from the lipid surface.

Hydrolysis of phosphatidylcholine liposomes by lysosomal phospholipase A is maximal at the phase transition temperature of the lipid substrate

1985 ◽  
Vol 5 (6) ◽  
pp. 477-482 ◽  
Author(s):  
Michel Vandenbranden ◽  
Georges De Gand ◽  
Robert Brasseur ◽  
Fabienne Defrise-Quertain ◽  
Jean-Marie Ruysschaert
Keyword(s):  
Phase Transition ◽  
Liquid Crystalline ◽  
Temperature Characteristic ◽  
Phosphatidylcholine Liposomes ◽  
Pancreatic Phospholipase ◽  
Pancreatic Phospholipase A2 ◽  
Rate Of Hydrolysis ◽  
Structural Analogy ◽  
Hydrolysis Of ◽  
Crystalline Phase Transition

We have measured the rate of hydrolysis of liposomes made of DL-α-dipalmitoylphosphatidylcholine (DPPC) and L-α-dimyristoylphosphatidylcholine by a soluble fraction of highly purified lysosomes isolated from rat liver. Phospholipids are hydrolyzed into lysophospho-lipids and fatty acids at a rate which is maximal near the temperature characteristic of the gel to liquid crystalline phase transition of the lipid bilayer. This strong influence of the physical properties of the substrate on the enzyme activity suggests a structural analogy between the lysosomal phospholipases of the A type (EC 3.1.1.32 and EC 3.1.1.4) and the pancreatic phospholipase A2.

The Influence of Lamellar Liquid Crystalline Media in the Hydrolysis of 4-Substituted Benzylidene t-Butylamine N-Oxides

1983 ◽  
Vol 90 (3-4) ◽  
pp. 307-321 ◽  
Author(s):  
W. E. Bacon ◽  
M. E. Neubert ◽  
P. J. Wildman ◽  
D. W. Ott
Keyword(s):  
Liquid Crystalline ◽  
Hydrolysis Of

Studies of Dlalkyl Ether Phospholipids. II. Requirement for a Liquid-Crystalline Substrate for Hydrolysis by Cabbage Leaf Phospholipase D

1971 ◽  
Vol 49 (12) ◽  
pp. 1362-1375 ◽  
Author(s):  
Jung-shou Chen ◽  
Peter G. Barton
Keyword(s):  
Diethyl Ether ◽  
Phospholipase D ◽  
Liquid Crystalline ◽  
Sodium Dodecyl ◽  
Crystalline Substrate ◽  
Hydrolytic Reaction ◽  
Hydrolysis Rates ◽  
Egg Lecithin ◽  
Ether Phospholipids ◽  
Hydrolysis Of

The hydrolysis of 1,2-ditetradecyl-, 1,2-dihexadecyl-, and 1,2-dioctadecyk-sn-glycero-3-phosphoryl-cholines by the soluble phospholipase D (EC 3.14.4) from cabbage leaf has been compared with that of egg lecithin. When a diethyl ether – chloroform mixture was used as activator low hydrolysis rates were observed for the dialkyl ether phospholipids because of their poor solubility in diethyl ether. Under these conditions the compounds did not inhibit the hydrolysis of egg lecithin. The hydrolytic reaction appeared to take place at the solvent–water interface resulting in a gradual denaturation of the enzyme. When sodium dodecyl sulfate was used as activator faster hydrolysis was evident due in part to a reduction in mesomorphic transition temperature (Tm) revealed by differential thermal analysis. Rates of hydrolysis of the homologous dialkyl ether phospholipids were inversely proportional to their Tm values in excess water. Under conditions required for effective hydrolysis of these compounds they inhibited the hydrolysis of egg lecithin. From studies of hydrolysis rates obtained with various combinations of phosphatidylcholine and phosphatidic acid analogues it was concluded that binding of enzyme to phospholipids and their subsequent hydrolysis required both an appropriate surface charge and a gel to liquid-crystalline phase transition in the substrate.

Fine Structural Localization of Acyltransferases Involved in Lipid Synthesis in Intestinal Mucosa.

1970 ◽  
Vol 28 ◽  
pp. 54-55
Author(s):  
R. J. Barrnett ◽  
J. A. Higgins
Keyword(s):  
Smooth Endoplasmic Reticulum ◽  
Lipid Synthesis ◽  
Mucosal Cell ◽  
Structural Localization ◽  
Morphological Studies ◽  
Mucosal Cells ◽  
Initial Appearance ◽  
Sh Group ◽  
Hydrolysis Of ◽  
Intestinal Mucosal Cells

The main products of intestinal hydrolysis of dietary triglycerides are free fatty acids and monoglycerides. These form micelles from which the lipids are absorbed across the mucosal cell brush border. Biochemical studies have indicated that intestinal mucosal cells possess a triglyceride synthesising system, which uses monoglyceride directly as an acylacceptor as well as the system found in other tissues in which alphaglycerophosphate is the acylacceptor. The former pathway is used preferentially for the resynthesis of triglyceride from absorbed lipid, while the latter is used mainly for phospholipid synthesis. Both lipids are incorporated into chylomicrons. Morphological studies have shown that during fat absorption there is an initial appearance of fat droplets within the cisternae of the smooth endoplasmic reticulum and that these subsequently accumulate in the golgi elements from which they are released at the lateral borders of the cell as chylomicrons.We have recently developed several methods for the fine structural localization of acyltransferases dependent on the precipitation, in an electron dense form, of CoA released during the transfer of the acyl group to an acceptor, and have now applied these methods to a study of the fine structural localization of the enzymes involved in chylomicron lipid biosynthesis. These methods are based on the reduction of ferricyanide ions by the free SH group of CoA.

Freeze fracture imaging and computer simulation of liposome structure: Membrane geometry and defects

1983 ◽  
Vol 41 ◽  
pp. 646-647
Author(s):  
Joseph A. Zasadzinski
Keyword(s):  
Liquid Crystalline ◽  
Freeze Fracture ◽  
Continuum Theory ◽  
Closed Surfaces ◽  
Straight Line ◽  
Low Weight ◽  
Concentric Spheres ◽  
Membrane Geometry ◽  
Dupin Cyclides ◽  
Limiting Case

At low weight fractions, many surfactant and biological amphiphiles form dispersions of lamellar liquid crystalline liposomes in water. Amphiphile molecules tend to align themselves in parallel bilayers which are free to bend. Bilayers must form closed surfaces to separate hydrophobic and hydrophilic domains completely. Continuum theory of liquid crystals requires that the constant spacing of bilayer surfaces be maintained except at singularities of no more than line extent. Maxwell demonstrated that only two types of closed surfaces can satisfy this constraint: concentric spheres and Dupin cyclides. Dupin cyclides (Figure 1) are parallel closed surfaces which have a conjugate ellipse (r1) and hyperbola (r2) as singularities in the bilayer spacing. Any straight line drawn from a point on the ellipse to a point on the hyperbola is normal to every surface it intersects (broken lines in Figure 1). A simple example, and limiting case, is a family of concentric tori (Figure 1b).To distinguish between the allowable arrangements, freeze fracture TEM micrographs of representative biological (L-α phosphotidylcholine: L-α PC) and surfactant (sodium heptylnonyl benzenesulfonate: SHBS)liposomes are compared to mathematically derived sections of Dupin cyclides and concentric spheres.

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