More on Arrhenius plots

Arrhenius plots of the non-latent UDP-glucuronyltransferase (p-nitrophenol acceptor) activity of guinea-pig microsomal membranes prepared with 154 mM-KCl were linear from 5 to 40 degrees C. Arrhenius plots for other microsomal preparations from guinea pig and rat liver that show various degrees of transferase latency, exhibited two linear regions intersecting at a sharp transition point near 20-25 degrees C. This discontinuity was abolished or greatly decreased when transferase latency was removed by treating the membranes with perturbants of phospholipid bilayer strucutre. The fluorescent probe N-phenyl-1-naphthyl-amine detected a thermotropic change in the fluidity of the phospholipid acyl chains of all the microsomal membrane preparations studied, at temperatures close to those of the Arrhenius-plot transitions. It is concluded that the thermotropic change in the structure of the membrane bilayer probably is a ‘phase separation’ or clustering of phospholipids, which affects a permeability barrier that restricts access of substrate to the transferase molecules.

Download Full-text

The influence of pH and temperature on the stability of flutamide. An HPLC investigation and identification of the degradation product by EI+-MS

RSC Advances ◽

10.1039/c4ra13617a ◽

2015 ◽

Vol 5 (5) ◽

pp. 3206-3214 ◽

Cited By ~ 4

Author(s):

R. N. El-Shaheny ◽

K. Yamada

Keyword(s):

Degradation Product ◽

Degradation Kinetics ◽

Hplc Method ◽

Profile Curve ◽

Arrhenius Plots ◽

Stability Indicating ◽

The Stability ◽

Rate Profile ◽

Influence Of Ph

Stability of flutamide was investigated using validated stability-indicating HPLC method. Degradation kinetics, Arrhenius plots, and pH-rate profile curve were explored.

Download Full-text

Phenobarbital selectively modulates the glucagon-stimulated activity of adenylate cyclase by depressing the lipid phase separation occurring in the outer half of the bilayer of liver plasma membranes

Biochemical Journal ◽

10.1042/bj1970675 ◽

1981 ◽

Vol 197 (3) ◽

pp. 675-681 ◽

Cited By ~ 48

Author(s):

M D Houslay ◽

I Dipple ◽

L M Gordon

Keyword(s):

Adenylate Cyclase ◽

Spin Probe ◽

Plasma Membranes ◽

Chemical Constituents ◽

Lipid Phase ◽

Lipid Phase Transition ◽

Arrhenius Plots ◽

Lipid Environment ◽

Lipid Phase Separation ◽

Outer Half

The glucagon-stimulated (coupled) activity of rat liver plasma-membrane adenylate cyclase could be selectively modulated by the anionic drug phenobarbital, whereas the fluoride-stimulated (uncoupled) activity remained unaffected. It is suggested that the cationic drug phenobarbital preferentially interacts with the external half of the bilayer, as the negatively charged phospholipids are found at the cytosol-facing side. This results in a selective fluidization of the external half of the bilayer, leading to a depression in the high-temperature onset of the lipid phase transition (from 28 degree to 16 degree C) occurring there. This was detected both by e.s.r. analysis, using a fatty acid spin probe, and also by Arrhenius plots of glucagon-stimulated activity, where the enzyme forms a transmembrane complex with the receptor and is sensitive to the lipid environment of both halves of the bilayer. However, in the absence of hormone, adenylate cyclase only senses the lipid environment of the inner (cytosol) half of the bilayer. Thus its fluoride stimulated activity and Arrhenius plots of this activity remained unaffected by the presence of phenobarbital (less than 12 mM) in the assay. These results support the view that independent modulation of the fluidity or chemical constituents of each half of the bilayer can selectively affect the receptor-coupled and uncoupled activities of adenylate cyclase.

Download Full-text

The activity of glucagon-stimulated adenylate cyclase from rat liver plasma membranes is modulated by the fluidity of its lipid environment

Biochemical Journal ◽

10.1042/bj1740179 ◽

1978 ◽

Vol 174 (1) ◽

pp. 179-190 ◽

Cited By ~ 114

Author(s):

I Dipple ◽

M D Houslay

Keyword(s):

Adenylate Cyclase ◽

Benzyl Alcohol ◽

Plasma Membranes ◽

Break Point ◽

Alcohol Concentration ◽

Cyclase Activity ◽

Adenylate Cyclase Activity ◽

Lipid Phase ◽

Glucagon Receptor ◽

Arrhenius Plots

1. The local anaesthetic benzyl alcohol progressively activated glucagon-stimulated adenylate cyclase activity up to a maximum at 50 mM-benzyl alcohol. Further increases in benzyl alcohol concentration inhibited the activity. The fluoride-stimulated adenylate cyclase activity was similarly affected except for an inhibition of activity occurring at low benzyl alcohol concentrations (approx. 10 mM. 2. The fluoride-stimulated adenylate cyclase activity of a solubilized enzyme preparation was unaffected by any of the benzyl alcohol concentrations tested. 3. Increases in 3-phenylpropan-1-ol and 5-phenylpentan-1-ol concentrations progressively activated both the fluoride- and glucagon-stimulated adenylate cyclase activities up to a maximum, above which further increases in alcohol concentration inhibited the activities. 4. The ‘break’ points in Arrhenius plots of glucagon-stimulated adenylate cyclase activity in native plasma membranes, and in plasma membranes fused with synthetic dimyristoyl phosphatidylcholine so as to constitute 60% of the total lipid pool, were decreased by approx. 6 degrees C by addition of 40 mM-benzyl alcohol. This was accompanied by a fall in the associated activation energies. 6. Arrhenius plots of fluoride-stimulated adenylate cyclase activity in the presence and absence of 40 mM-benzyl alcohol were linear, although addition of benzyl alcohol caused a dramatic decrease in the associated activation energy of the reaction. 7. 5′-Nucleotidase activity was stimulated by benzyl alcohol, and the ‘break’ point in the Arrhenius plot of its activity was decreased by about 6 degrees C by addition of 40 mM-benzyl alcohol to the assay. 8. It is suggested that benzyl alcohol effects a fluidization of the bilayer, which is clearly demonstrated by its ability to lower the temperature of a lipid phase separation occurring at 28 degrees C in the outer half of the bilayer to around 22 degrees C. The increase in bilayer fluidity relieves a physical constraint on the membrane-bound adenylate cyclase, activating the enzyme. 9. The various inhibition phenomena are discussed in detail, together with the suggestion that the interaction between the uncoupled catalytic unit of adenylate cyclase and the lipids of the bilayer is altered on its physical coupling to the glucagon receptor.

Download Full-text

Effects of acute warming on cardiac and myotomal sarco(endo)plasmic reticulum ATPase (SERCA) of thermally acclimated brown trout (Salmo trutta)

Journal of Comparative Physiology B ◽

10.1007/s00360-020-01313-1 ◽

2020 ◽

Author(s):

Matti Vornanen

Keyword(s):

High Temperatures ◽

Brown Trout ◽

Salmo Trutta ◽

Thermal Inactivation ◽

Cyclopiazonic Acid ◽

Temperature Acclimation ◽

Limiting Factor ◽

Arrhenius Plots ◽

Plasmic Reticulum ◽

Beating Rate

Abstract At high temperatures, ventricular beating rate collapses and depresses cardiac output in fish. The role of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) in thermal tolerance of ventricular function was examined in brown trout (Salmo trutta) by measuring heart SERCA and comparing it to that of the dorsolateral myotomal muscle. Activity of SERCA was measured from crude homogenates of cold-acclimated (+ 3 °C, c.a.) and warm-acclimated (+ 13 °C, w.a.) brown trout as cyclopiazonic acid (20 µM) sensitive Ca2+-ATPase between + 3 and + 33 °C. Activity of the heart SERCA was significantly higher in c.a. than w.a. trout and increased strongly between + 3 and + 23 °C with linear Arrhenius plots but started to plateau between + 23 and + 33 °C in both acclimation groups. The rate of thermal inactivation of the heart SERCA at + 35 °C was similar in c.a. and w.a. fish. Activity of the muscle SERCA was less temperature dependent and more heat resistant than that of the heart SERCA and showed linear Arrhenius plots between + 3 and + 33 °C in both c.a. and w.a. fish. SERCA activity of the c.a. muscle was slightly higher than that of w.a. muscle. The rate of thermal inactivation at + 40 °C was similar for both c.a. and w.a. muscle SERCA at + 40 °C. Although the heart SERCA is more sensitive to high temperatures than the muscle SERCA, it is unlikely to be a limiting factor for heart rate, because its heat tolerance, unlike that of the ventricular beating rate, was not changed by temperature acclimation.

Download Full-text