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J G Reich

Publications and source records attributed to J G Reich.

At least 37 records · Page 2Linked to original sources
PubMed1980

Theoretical study of an energy metabolizing system satisfying Mitchell's postulates.

An energy metabolizing system was modelled, which carries as characteristic features substrate uptake and product extrusion, respiration and ATP-synthesis, coupled by the protonmotive potential corresponding to Mitchell's chemiosmotic hypothesis of oxidative phosphorylation. The influence of the electric part of the protonmotive potential on the rate laws of the different processes has been taken into account by a phenomenological exponent of the proton concentration, thus fortifying the osmotic concentration part of the protonmotive potential. The steady-state behaviour of the model was investigated. It could be shown that a model of such kind reveals multistationarity, homeostasis and trigger behaviour. Curves of respiration control (respiration velocity over ADP/(ATP + ADP) or ATP/ADP) are in qualitative accordance with experimental facts (state 3 and state 4 of mitochondria) as well as curves describing the effect of uncouplers on the respiratory rate.

Adenosine Triphosphate↗
PubMed1978

[Importance of binding of 2,3-diphosphoglycerate and ATP to hemoglobin for erythrocyte glycolysis: activation by 2,3-diphosphoglycerate of hexokinase at intracellular conditions].

In a theoretical study the influence of hemoglobin and Mg-ions as binding partners of red cell 2,3-diphosphoglycerate and ATP was investigated. Free hemoglobin may be an efficient competitor of Mg2+ for the ligand ATP. At conditions which favour hemoglobin as binding partner (i.e. desoxygenation, low medium pH and incubation temperature, as in blood preservation) up to 95% of the whole cellular ATP (ca. 2mM in cell water) may be bound to hemoglobin (ca. 7 mM). This binding is largely prevented in the presence of physiological amounts of diphosphoglycerate (ca. 7 mM) which is in excess and has a higher binding affinity to hemoglobin. Therefore, diphosphoglycerate keeps ATP (MgATP) in cell water solution at conditions in which Hb would trop it in the presence of Mg2+ (ca. 3mM). It can be calculated that, by lack of free MgATP, the activity of hexokinase within the cell drops by a factor of greater than 10 when diphosphoglycerate is metabolized. This indirect activation by diphosphoglycerate of hexokinase is operative at free concentrations of DPG far below those which exert the well known excess inhibitory effect on hexokinase and phosphofructokinase. In a model study, the activation by diphosphoglycerate of the initial two-kinase stage was introduced into a simplified kinetic model of glycolysis. A pronounced hysteresis loop of the stationary concentrations of ATP and diphosphoglycerate was produced indicating the existence of several stationary states, one with high ATP and high diphosphoglycerate, the other one with low values. It is demonstrated that diphosphoglycerate, being a protector of glycolysis at physiological concentrations, triggers an autocatalytic breakdown of the energy state when permitted to drop to low values.

Adenosine Triphosphate↗
PubMed1978

[Theoretical studies on the influence of binding constants of hemoglobin for ATP and 2,3-diphosphoglycerate on erythrocyte glycolysis].

In the red blood cell exist a binding equilibrium of ATP and 2,3-DPG with hemoglobin. For the metabolism only the free active levels of organic phosphates are relevant. The binding constants of hemoglobin increase with decreasing temperature and pH. Using a stoichometric model of glycolysis, the change of free concentrations by altered binding constants and its import on the energy metabolism of the erythrocyte was theoretically studied. The results are: 1. Total ATP-content (bound plus free ATP) does not depend on the binding properties of hemoglobin. 2. Total 2,3-DPG-content is changed by altered binding constants of hemoglobin. The direction of change depends on the ratio energy-consumption/substrate-uptake. 3. In the case of strong binding of organic phosphates to hemoglobin the experimentally measurable total ATP-content does not reflect the free ATP-concentration in the cell water. As a result of binding, free ATP may be low even if total ATP is unchanged. 4. The free concentration of 2,3-DPG always parallels the total content.

Adenosine Triphosphate↗
PubMed1977

[Effect of rapid changes of the oxygenation state and other external parameters on the long-term behavior of the energy metabolism in the erythrocyte].

The red blood cell when transported through the circulatory system is exposed to a steady (approximately periodical) change of environmental conditions causing a permanent fluctuation of its important metabolic parameters. In a simple theoretical model it is demonstrated that a rapid oscillation of such parameters may stabilize a metabolic state which will collapse when this oscillation breaks off. The hypothesis is advanced that parameter oscillations caused by the physiological function of the red blood cell may be of importance for the maintenance of its energy metabolism and that the break-off of these oscillations may be a potential cause for the metabolic collapse, e.g. in stored blood.

Adenosine Triphosphate↗
PubMed1975

Time hierarchy, equilibrium and non-equilibrium in metabolic systems.

A metabolic system consists of cooperating biochemical reactions. The motion is described by differential equations in the metabolites. The right-hand sides of these equations are linear combinations of the velocities of the individual reactions. These velocities depend in a non-linear manner on the metabolite concentrations (according to the law of mass action). A characteristic "metabolic" time may be defined for the motion of the whole system. It scales the essential metabolic events whose evolution time is comparable to this metabolite time unit. The constituent reactions of the metabolic system have an individual characteristic time which need not coincide with the general metabolic time. The individual time characterises the approach to the individual equilibrium of the isolated undisturbed reaction. According to the ratio of these two time scales, a single reaction may be fast, or slow, or essential, as compared with the metabolic events. Characteristic time of a single reaction and its steady-state deviation from equilibrium are closely related. It can be shown that the relative deviation from equilibrium of a reaction within the metabolic network is of the same numerical order as the ratio between individual time to metabolic time. The interaction of many reactions with different characteristic times introduces a time hierarchy into the system. This can be made transparent by appropriate scaling and by linear transformation of the system. The subsystem of fast cooperating reactions (dehydrogenases, phosphotransferases) attains a state which is near to the individual equilibrium and reestablishes this state after perturbation. The equilibration is fast; an ultrarapid phase of cofactor equilibrium can be distinguished from the fast phase of substrate equilibrium (exchange of metabolic material between different pathways). During the slower metabolic phase these near-equilibria manifest themselves as stoichiometric linkage between unrelated metabolites. The latter cease to be independent variables and combine to metabolic pools. It can be strictly shown that the essential variables at the metabolic time scale are carrier pools and the degree of occupancy of these carriers by metabolic groups. Chemically different types of carrier pools may be functionally linked together by fast reactions. A consequence of such an arrangement of reactions are distance effects: Changes at one end of a metabolic map may be directly conveyed to other pathways via stoichiometric linkage brought about by fast equilibration of cofactor reactions.

Enzymes↗
PubMed1975

Redox metabolism of glutathione in the red blood cell.

A theoretical study of the biochemical and clinical aspects of the reduction-oxidation metabolism of glutathione in the mature red blood cell is presented. A summarizing survey of the literature data has led to the formulation of a mathematical model which comprises the kinetic properties of the enzymes partaking in the hexose monophosphate pathway (HMP) and the oxidation of NADPH and GSH. The model takes the form of a system of differential equations describing the motion of metabolites in one cell. The interactions between metabolites ane enzymes, in particular between glutathione and the SH-dependent enzymes of glucose phosphorylation and HMP have been included into the model...

Disulfides↗