Photophosphorylation as Function of ADP Concentration at Varying Transmembrane Proton Gradients

1989 ◽  
Vol 44 (5-6) ◽  
pp. 473-479 ◽  
Author(s):  
Georg Heinen ◽  
Heinrich Strotmann
Keyword(s):  
Steady State ◽  
Kinetic Model ◽  
Light Intensity ◽  
Phosphate Concentration ◽  
Proton Gradient ◽  
Enzyme Kinetic ◽  
Fluorescence Technique ◽  
Proton Gradients ◽  
Atp Formation ◽  
External Ph

Abstract Rates of photophosphorylation were measured at constant saturating phosphate concentration , varying ADP concentration , and varying light intensity. As the transmembrane proton gradient is decreased by phosphorylation to different extents depending on the concentration of ADP . rates of ATP formation obtained at the different ADP concentrations were plotted versus the actual steady state ΔpH (in the absence of ΔΨ) during the course of the reaction . ΔpH was monitored by the calibrated 9-aminoacridine fluorescence technique. In secondary plots phosphorylation as function of ADP concentration at different constant ΔpH values were obtained . The results indicate Michaelis-Menten kinetics. The true Km for ADP is virtually unaffected by ΔpH whereas Vmax (at ADP saturation ) strongly depends on ΔpH . The results are discussed in the framework of a simple enzyme kinetic model which considers the intrathylakoidal proton (at constant external pH ) as a third substrate for ATP formation. The model is capable o f explaining the reported results as well as a variety of important results from the literature.

Kinetic analysis of mechanism of intestinal Na+-dependent sugar transport

1985 ◽  
Vol 248 (5) ◽  
pp. C498-C509 ◽  
Author(s):  
D. Restrepo ◽  
G. A. Kimmich
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Sugar Transport ◽  
Enzyme Kinetic ◽  
Steady State Distribution ◽  
State Distribution ◽  
Least Squares Fit ◽  
Coupling Stoichiometry ◽  
Rate Limiting ◽  
Kinetics Of

Zero-trans kinetics of Na+-sugar cotransport were investigated. Sugar influx was measured at various sodium and sugar concentrations in K+-loaded cells treated with rotenone and valinomycin. Sugar influx follows Michaelis-Menten kinetics as a function of sugar concentration but not as a function of Na+ concentration. Nine models with 1:1 or 2:1 sodium:sugar stoichiometry were considered. The flux equations for these models were solved assuming steady-state distribution of carrier forms and that translocation across the membrane is rate limiting. Classical enzyme kinetic methods and a least-squares fit of flux equations to the experimental data were used to assess the fit of the different models. Four models can be discarded on this basis. Of the remaining models, we discard two on the basis of the trans sodium dependence and the coupling stoichiometry [G. A. Kimmich and J. Randles, Am. J. Physiol. 247 (Cell Physiol. 16): C74-C82, 1984]. The remaining models are terter ordered mechanisms with sodium debinding first at the trans side. If transfer across the membrane is rate limiting, the binding order can be determined to be sodium:sugar:sodium.

pH dependence of kinetics and steady-state block of cardiac sodium channels by lidocaine

1993 ◽  
Vol 264 (5) ◽  
pp. H1588-H1598 ◽  
Author(s):  
D. J. Wendt ◽  
C. F. Starmer ◽  
A. O. Grant
Keyword(s):  
Steady State ◽  
Sodium Channel ◽  
Local Anesthetic ◽  
Ph Dependence ◽  
Membrane Depolarization ◽  
Low Ph ◽  
Proton Exchange ◽  
Phasic Block ◽  
Cardiac Sodium Channels ◽  
External Ph

The local anesthetic-class antiarrhythmic drugs produce greater depression of conduction in ischemic compared with normal myocardium. The basis for this relatively selective action is uncertain. A model of the pH-dependent interaction of tertiary amine drugs with the sodium channel suggests that the low pH occurring during ischemia slows drug dissociation from the channel by changing the drug's protonation. The importance of the proton exchange reaction and the effect of overall slowing of drug dissociation on steady-state sodium channel blockade is uncertain. We have measured whole cell sodium channel current in rabbit atrial myocytes during control and exposure to lidocaine while external pH was varied between 6.8 and 7.8 at membrane potentials of -140, -120, and -100 mV. Tonic blockade was little influenced by external pH. Decreasing the external pH from 7.8 to 6.8 slowed both the rate of development of phasic block and recovery from the block. Decreasing the membrane potential from -140 to -100 mV increased the degree of phasic block attained in the steady state. Block was further enhanced when low pH was combined with membrane depolarization. Experiments in which deuterium ions were substituted for protons suggest that the kinetics of proton exchange is not rate limiting in the dissociation of drugs from the sodium channel. We conclude that it is the combined effect of low pH and membrane depolarization that may be critical in the enhanced blocking action of local anesthetic-class drugs during ischemia.

Serial analysis of renal blood flow by positron tomography with rubidium-82

1986 ◽  
Vol 251 (5) ◽  
pp. H1024-H1030
Author(s):  
N. Tamaki ◽  
C. A. Rabito ◽  
N. M. Alpert ◽  
T. Yasuda ◽  
J. A. Correia ◽  
...  
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Kinetic Model ◽  
Renal Blood Flow ◽  
Constant Infusion ◽  
Flow Reduction ◽  
Arterial Blood ◽  
Steady State Kinetic ◽  
State Kinetic ◽  
Rubidium 82

To determine whether renal blood flow can be measured by positron-emission tomography (PET) during constant infusion of rubidium-82 (82Rb) using a steady-state kinetic model, studies were performed in 10 dogs at control (n = 10), during mild flow reduction (n = 7), during severe flow reduction (n = 10), and after reperfusion of the kidney (n = 3). PET data were quantified to determine mean concentration of 82Rb (Ct) in each transverse section of the kidney. The arterial concentration (Ca) of 82Rb was measured by well counting of arterial blood samples during the equilibrium scan. 82Rb renal uptake (Ct/Ca) correlated nonlinearly with microsphere renal blood flow according to a steady-state kinetic model (r = 0.90). 82Rb estimated flow was 3.16 +/- 1.36 ml X min-1 X g-1 at control and 1.56 +/- 0.57 and 0.37 +/- 0.59 during mild and severe flow reductions, respectively. Microsphere determined flow was 2.89 +/- 0.77 ml X min-1 X g-1 at control, 1.58 +/- 0.42 at mild reduction, and 0.27 +/- 0.49 at severe reduction. In the occlusion and reperfusion model, the 82Rb estimated flow during occlusion was 0.21 +/- 0.15 ml X min-1 X g-1 and on reperfusion went up to 2.13 +/- 1.08. The contralateral kidney demonstrated reductions in the 82Rb estimated flow of 3.02 +/- 1.62 ml X min-1 X g-1 (63%) and 2.92 +/- 0.89 (61%) during mild and severe flow reductions, respectively. We conclude that PET with 82Rb permits serial quantitative assessment of renal flood flow.

scholarly journals Accelerating Kinetic Parameter Identification by Extracting Information from Transient Data: A Hydroprocessing Study Case

Catalysts ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 361
Author(s):  
Ngoc-Yen-Phuong Cao ◽  
Benoit Celse ◽  
Denis Guillaume ◽  
Isabelle Guibard ◽  
Joris W. Thybaut
Keyword(s):  
Steady State ◽  
Experimental Design ◽  
Kinetic Model ◽  
Kinetic Modeling ◽  
Sufficient Data ◽  
Design Algorithm ◽  
State Data ◽  
Transient Data ◽  
Study Case ◽  
The One

Hydroprocessing reactions require several days to reach steady-state, leading to long experimentation times for collecting sufficient data for kinetic modeling purposes. The information contained in the transient data during the evolution toward the steady-state is, at present, not used for kinetic modeling since the stabilization behavior is not well understood. The present work aims at accelerating kinetic model construction by employing these transient data, provided that the stabilization can be adequately accounted for. A comparison between the model obtained against the steady-state data and the one after accounting for the transient information was carried out. It was demonstrated that by accounting for the stabilization, combined with an experimental design algorithm, a more robust and faster manner was obtained to identify kinetic parameters, which saves time and cost. An application was presented in hydrodenitrogenation, but the proposed methodology can be extended to any hydroprocessing reaction.

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