Physiological equilibrium

The presence of S. mutans and other cariogenic bacteria contributes towards the formation of a biofilm known as dental plaque, and their metabolism of fermentable carbohydrates in the diet leads to the formation of acids [12]. Dental caries has been described as a complex imbalance in physiologic equilibrium between tooth mineral and biofilm [13]. Biofilms imply the involvement of microbiological species [14], but the key concept included within this definition is that the bacteria involved are native to the body, not a group of specific invasive bacteria causing infection [14]. 

Figure 5.7 Comparison of GTPase timing for physiological (non-equilibrium) and non-physiological (equilibrium) cases. Results at cellular phosphorylation potential (AG gtp = -bOkJ-mor1) are plotted as solid lines results at equilibrium (AG gtp = 0) are plotted as dashed lines. The top panel plots piwit), the probability that the G protein is in the GTP-bound state given that it is in the state Ggtp at t = 0. The bottom panel plots fj t) the probability distribution of dwell time in the GTP-bound state. See text for details and parameter values.

Fig. 4.12. Trees with too strong shoot growth are not in physiological equilibrium and will not give the best possible yield.

Maintaining a physiological equilibrium (= concentration) of cell-formed reactive oxygen intermediates by means of highly sensitive regulation mechanisms is a fundamental process of biomolecular homoeostasis. 

The normal functioning of the central nervous system (CNS) presupposes a well-balanced interaction between different biochemically and structurally linked neuronal systems. When one member of a neuronal circuit is altered in its structural or biochemical entity, an imbalance in the functional system results and a compensatory mechanism must be activated in order to maintain physiological equilibrium. 

Neurons maintained in primary culture are exquisitely sensitive to any compound that alters then-physiological equilibrium by changing ion fluxes [40,41] or altering their biochemical steady state... 

Gross believes that disturbance of the water supply is the principal cause of spruce deaths. According to Kleinschmidt the physiological equilibrium of the soil profile is the main cause. 

Homeostasis A state of physiological equilibrium produced by a balance of functions and chemical composition within an organism. 

Here again two cases can be distinguished. With in vitro measurements there is no great difference in practical techniques as compared to other samples (see Chap. 5), aside from the complexity of the sample matrix. In contrast to other fields of application, however, in biological systems the danger always exists that the sampling process may influence the physiological equilibrium. The consequence of such a disturbance is that no matter how accurately an analysis is carried out, the actual variable of interest is not measured. This problem is reduced with in situ or in vivo measurements however, here problems of sterilization and electrode calibration come up. 

Ag, convention for the equilibrium dissociation constant of an antagonist-receptor complex usually determined in a functional assay denoting antagonism of a physiological response, although it can be associated with an antagonist when it is used in other types of experiment. It has units of M and is the concentration that occupies half the receptor population at equilibrium. It also can be thought of as the reciprocal of affinity. 

The method is very useful for the synthesis of physiologically interesting a-mcthylamino acids, e.g., methyl dopa from the 3,4-dimethoxybenzyl derivative. The excellent stereoselection achieved in the process, however, is caused by the preferential crystallization of one pure diastereomerfrom the equilibrium mixture formed in the reversible Strecker reaction. Thus, the pure diastcrcomers with benzyl substituents, dissolved in chloroform or acetonitrile, give equilibrium mixtures of both diastereomers in a ratio of about 7 347. This effect has also been found for other s-methylamino nitriles of quite different structure49. If the amino nitrile (R1 = Bn) is synthesized in acetonitrile solution, the diastereomers do not crystallize while immediate hydrolysis indicates a ratio of the diastereomeric amino nitriles (S)I(R) of 86 1447. 

Under physiological conditions, transfer of Et3PAufrom hemoglobin to albumin has been observed. The transfer is direct and does not require a low-molecular weight thiol such as GSH as an intermediary and indicates that inter-protein transfer of gold can occur spontaneously. The rapid and efficient manner of establishing this equilibrium (for transauration ) could determine many ofthe effects of intracellular and extracellular chemistry of gold. 

The abasic sites (3, Scheme 8.2) resulting from the loss of alkylated bases from DNA are both cytotoxic and mutagenic. " The cyclic acetal (3) exists in equilibrium with small amounts (—1%) of the open chain aldehyde (4). The acidic nature of a-proton in the aldehyde form of the abasic lesion facilitates 3-elimination of the 3 -phosphate residue to yield a strand break. " This reaction occurs with a half-life of about 200 h under physiological conditions (pH 7.4, 37°C), but can be accelerated by heat, basic conditions, or the presence of various amines. " ... 

Generation of superoxide radical under physiological conditions ultimately leads to the production of hydroxyl radical through a cascade of redox reactions. Initially, sn-peroxide disproportionates to generate hydrogen peroxide (Eq. 3, Scheme 8.36) Superoxide radical exists in equilibrium with its protonated form (H02, = 5). 

Competition for binding to heparin (in essentially salt-free solutions) has been studied for most physiological cations, by ion-exchange,372 equilibrium dialysis,373 c.d.,365 and 23Na-n.m.r. spectroscopy.370 The following order of affinity was generally observed Na+ < K+ < Mg2+ < Ca2+. 

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