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A Futile Redox Cycle Involving Neuroglobin Observed at Physiological Temperature.

Liu A, Brittain T - Int J Mol Sci (2015)

Bottom Line: Determination of the rate constants for each of the steps in the cycle allows us to mathematically model the steady state concentration of the active anti-apoptotic ferrous form of neuroglobin under various conditions.Temporal analysis of this model indicates that the transition from low concentrations to high concentration of ferrous neuroglobin occurs on the seconds time scale.In this way the cell avoids unwanted increased oncogenic potential under normal conditions, but the rapid activation of neuroglobin provides anti-apoptotic protection in times of acute hypoxia.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Auckland, Auckland 1142, New Zealand. a.liu@auckland.ac.nz.

ABSTRACT
Previous studies identifying the potential anti-apoptotic role of neuroglobin raise the question as to how cells might employ neuroglobin to avoid the apoptotic impact of acute hypoxia whilst also avoiding chronic enhancement of tumour formation. We show that under likely physiological conditions neuroglobin can take part in a futile redox cycle. Determination of the rate constants for each of the steps in the cycle allows us to mathematically model the steady state concentration of the active anti-apoptotic ferrous form of neuroglobin under various conditions. Under likely normal physiological conditions neuroglobin is shown to be present in the ferrous state at approximately 30% of its total cellular concentration. Under hypoxic conditions this rapidly rises to approximately 80%. Temporal analysis of this model indicates that the transition from low concentrations to high concentration of ferrous neuroglobin occurs on the seconds time scale. These findings indicate a potential control model for the anti-apoptotic activity of neuroglobin, under likely physiological conditions, whereby, in normoxic conditions, the anti-apoptotic activity of neuroglobin is maintained at a low level, whilst immediately a transition occurs to a hypoxic situation, as might arise during stroke, the anti-apoptotic activity is drastically increased. In this way the cell avoids unwanted increased oncogenic potential under normal conditions, but the rapid activation of neuroglobin provides anti-apoptotic protection in times of acute hypoxia.

No MeSH data available.


Related in: MedlinePlus

Concentration dependence of carbon monoxide binding to deoxy-ferrous neuroglobin. Reaction rates observed in stopped-flow experiments are shown as a function of carbon monoxide concentration (points). The data were best-fitted to a hyperbolic function (line r2 = 0.94). The error bars represent the standard error seen for replicate experiments (different protein preparations used on different days). Technical replicate values fell within the diameter of the symbol.
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ijms-16-20082-f001: Concentration dependence of carbon monoxide binding to deoxy-ferrous neuroglobin. Reaction rates observed in stopped-flow experiments are shown as a function of carbon monoxide concentration (points). The data were best-fitted to a hyperbolic function (line r2 = 0.94). The error bars represent the standard error seen for replicate experiments (different protein preparations used on different days). Technical replicate values fell within the diameter of the symbol.

Mentions: At 37 °C the reaction of reduced wild type human neuroglobin with carbon monoxide followed a simple exponential time course (kobs) at any particular concentration of carbon monoxide investigated. The concentration dependence of the observed rate constant for the process of carbon monoxide binding followed a simple hyperbolic form (Figure 1) as expected from Equation (1). Using the literature value for the binding of CO to the five co-ordinated form of neuroglobin (5.7 × 107 M−1·s−1 at 37 °C [28]). Non-linear least squares fitting of this hyperbolic dependence in terms of competition between the binding of the intrinsic histidine (His64) and the extrinsic ligand according to Equation (1)kobs = kHis off × kCO [CO] (kHis on + kHis off + kCO [CO])(1)yields values for the rate constants for the binding (kHis on) and the dissociation (kHis off) of the intrinsic His64 ligand of 4300 and 1.26 s−1. Reaction of dithiothrietol (DTT) reduced neuroglobin with oxygenated buffer yielded rate constants for the oxygen binding process identical to those observed for the reaction with carbon monoxide, adding support to the view that reaction of reduced neuroglobin with gaseous ligands is controlled by the dissociation and association rates of the intrinsic His heme ligand.


A Futile Redox Cycle Involving Neuroglobin Observed at Physiological Temperature.

Liu A, Brittain T - Int J Mol Sci (2015)

Concentration dependence of carbon monoxide binding to deoxy-ferrous neuroglobin. Reaction rates observed in stopped-flow experiments are shown as a function of carbon monoxide concentration (points). The data were best-fitted to a hyperbolic function (line r2 = 0.94). The error bars represent the standard error seen for replicate experiments (different protein preparations used on different days). Technical replicate values fell within the diameter of the symbol.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4581342&req=5

ijms-16-20082-f001: Concentration dependence of carbon monoxide binding to deoxy-ferrous neuroglobin. Reaction rates observed in stopped-flow experiments are shown as a function of carbon monoxide concentration (points). The data were best-fitted to a hyperbolic function (line r2 = 0.94). The error bars represent the standard error seen for replicate experiments (different protein preparations used on different days). Technical replicate values fell within the diameter of the symbol.
Mentions: At 37 °C the reaction of reduced wild type human neuroglobin with carbon monoxide followed a simple exponential time course (kobs) at any particular concentration of carbon monoxide investigated. The concentration dependence of the observed rate constant for the process of carbon monoxide binding followed a simple hyperbolic form (Figure 1) as expected from Equation (1). Using the literature value for the binding of CO to the five co-ordinated form of neuroglobin (5.7 × 107 M−1·s−1 at 37 °C [28]). Non-linear least squares fitting of this hyperbolic dependence in terms of competition between the binding of the intrinsic histidine (His64) and the extrinsic ligand according to Equation (1)kobs = kHis off × kCO [CO] (kHis on + kHis off + kCO [CO])(1)yields values for the rate constants for the binding (kHis on) and the dissociation (kHis off) of the intrinsic His64 ligand of 4300 and 1.26 s−1. Reaction of dithiothrietol (DTT) reduced neuroglobin with oxygenated buffer yielded rate constants for the oxygen binding process identical to those observed for the reaction with carbon monoxide, adding support to the view that reaction of reduced neuroglobin with gaseous ligands is controlled by the dissociation and association rates of the intrinsic His heme ligand.

Bottom Line: Determination of the rate constants for each of the steps in the cycle allows us to mathematically model the steady state concentration of the active anti-apoptotic ferrous form of neuroglobin under various conditions.Temporal analysis of this model indicates that the transition from low concentrations to high concentration of ferrous neuroglobin occurs on the seconds time scale.In this way the cell avoids unwanted increased oncogenic potential under normal conditions, but the rapid activation of neuroglobin provides anti-apoptotic protection in times of acute hypoxia.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Auckland, Auckland 1142, New Zealand. a.liu@auckland.ac.nz.

ABSTRACT
Previous studies identifying the potential anti-apoptotic role of neuroglobin raise the question as to how cells might employ neuroglobin to avoid the apoptotic impact of acute hypoxia whilst also avoiding chronic enhancement of tumour formation. We show that under likely physiological conditions neuroglobin can take part in a futile redox cycle. Determination of the rate constants for each of the steps in the cycle allows us to mathematically model the steady state concentration of the active anti-apoptotic ferrous form of neuroglobin under various conditions. Under likely normal physiological conditions neuroglobin is shown to be present in the ferrous state at approximately 30% of its total cellular concentration. Under hypoxic conditions this rapidly rises to approximately 80%. Temporal analysis of this model indicates that the transition from low concentrations to high concentration of ferrous neuroglobin occurs on the seconds time scale. These findings indicate a potential control model for the anti-apoptotic activity of neuroglobin, under likely physiological conditions, whereby, in normoxic conditions, the anti-apoptotic activity of neuroglobin is maintained at a low level, whilst immediately a transition occurs to a hypoxic situation, as might arise during stroke, the anti-apoptotic activity is drastically increased. In this way the cell avoids unwanted increased oncogenic potential under normal conditions, but the rapid activation of neuroglobin provides anti-apoptotic protection in times of acute hypoxia.

No MeSH data available.


Related in: MedlinePlus