Free magnesium

Heated zirconium is readily chlorinated by ammonium chloride, molten stannous chloride, zinc chloride, and chlorinated hydrocarbons and the common chlorinating agents. It is slowly attacked by molten magnesium chloride in the absence of free magnesium, which is always present in the KroU process. 

For example, Bachelard used [Mgtotai]/[ATPtotai ] = 1 in his rate studies, and he obtained a slightly sigmoidal plot of initial velocity versus substrate ATP concentration. This culminated in the erroneous proposal that brain hexokinase was allosterically activated by magnesium ions and by magnesium ion-adenosine triphosphate complex. Purich and Fromm demonstrated that failure to achieve adequate experimental control over the free magnesium ion concentration can wreak havoc on the examination of enzyme kinetic behavior. Indeed, these investigators were able to account fully for the effects obtained in the previous hexokinase study. ... 

The most important point is that this procedure provides a reliable and effective way for dealing with metal ion interactions with nucleotides. By maintaining the free magnesium ion at a single fixed concentration, the experimenter avoids any chance of uncontrolled variation in the [MgATp2-]/[ATP -j ratio. 

Because muscle cells are especially rich in terms of phosphorus-containing metabolites (e.g., ATP, ADP, phos-phocreatine, and orthophosphate), nuclear magnetic resonance " has proved to be a valuable noninvasive probe of metabolic changes attending muscle activity. The spectral sensitivity of P is especially high relative to other nuclei, and one can detect cellular concentrations as low as 0.5 mM as well as utilize chemical shift data to define intracellular pH and free magnesium ion concentrations. See also Nuclear Magnetic Resonance Chemical Shift... 

E. Murphy, C. Steenbergen, L.A. Levy, B. Raju, R.E. London, Cytosolic free magnesium levels in ischemic rat-heart, J. Biol. Chem. 264 (1989) 5622-5627. 

Murphy E, Freudenreich CC, Levy LA, London RE, Liebermann M Monitoring cytosolic free magnesium in cultured chicken heart cells by use of the fluorescent indicator furaptra. Proc Natl Acad Sci USA... 

Figure 6-2 Plots of the apparent Gibbs energy AG f for hydrolysis of ATP as a function of pH at a series of different concentrations of free magnesium ions. Millimolar [Mg2+] is indicated by the numbers by the curves. Computer-drawn graphs courtesy of Carol M. Metzler.

The uptake of Mn2+ or Co2+ by system I is inhibitory or lethal respectively, and leads to efflux of Mg2+ from the cell. It is likely that accumulated Mn3+ or Co2+ displaces Mg2+ from ribosomes, thus increasing intracellular free magnesium ions, which leave the cell via the Mg2+ transport systems. 

Cyclic uptake and release of Ca2+ from the extracellular medium occur during mitosis in Physarum pofycephalum, and correlate with specific structural and kinetic events in the mitotic nuclei.442 The membrane system in the mitotic apparatus in Haemantkus endosperm cells functions in the localized release of Ca2+, so regulating the events of mitosis.443 It is known that calcium exerts effects on the stability of spindle microtubules. An alternative view is that free magnesium concentration acts as the fundamental regulator of the cell cycle.444 Tubulin polymerization depends on the presence of magnesium and the absence of calcium, and control of the Ca2+/Mg2+ ratio is relevant to spindle assembly. 

The method was designed for the determination of ionized (free) magnesium (iMg2"1") together with other major electrolytes (Na+, K+, Cl and Ca2+) and pH in blood serum, plasma or whole blood in the environment of the commercially available Microlyte 6 analyzer supplied by Thermo Fisher Scientific, Finland (previously KONE Instruments, Finland) [1-3]. 

Magnesium aluminate, the preferred support of one catalyst supplier, has a larger specific surface area. But this material must be calcined to a higher temperature during manufacture of the support particles to ensure it contains no free magnesium oxide, which would be hydrated to hydroxide at temperatures below 300 °C. This chemical change results in a volume increase, which would destroy the structure and impair the mechanical stability of the catalyst. 

In the study of phosphofructokinase (Figure 10.50), is there any evidence that free ATP inhibits the activity of the enzyme is there any evidence that free magnesium inhibits the enzvme ... 

This formula indicates that the concentration of the MP complex is dependent on those of M and P The foimula can be used to estimate the concentration of MP, with a knowledge of the total Mg and total ATP The cytosolic level of total Mg is about 10 mAf and that of ATP is about 2 mM. The value of K is taken from Table 10.16. The concentration [M] of free magnesium is 10 - [MP], The concentration [P] of free ATP is 2,0 - [MP). The value for the concentration [MP] of the Mg-ATF complex can easily be found from the following formula using a computer ... 

The second method involves reacting magnesium oxide with ferrosilicon. Ferrosilicon is an alloy of iron and silicon. When magnesium oxide and ferrosilicon react, free magnesium metal is formed. 

From these results, it can be concluded that the number and strength of acid sites on MgVAPO-5 and MgAPO-5 is higher than on VAPO-5 or VjOj/MgO samples. On the other hand, it has been proposed the presence of basic sites on V/MgO samples [1,2]. This basic sites are associated to vanadium-free magnesium sites on the catalyst surface. 

For an optimal reaction, it is important to keep Rho in an intact guanine nucleotide-binding conformation. The presence of free magnesium ion is essential for the reaction. The addition of guanine nucleotides is also helpful, but detergents such as Triton and Tween inhibit the reaction. For optimization, it is advisable to use a homogenization buffer without the detergent. 

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