Magnesium ionic strength dependence

An additional factor was found to influence the rate of reaction in the experiments involving tetrakis ( -mercaptoethylamine) trinickel (II) ion. The addition of nickel chloride retarded the process. Methanol was used as the solvent to demonstrate that the dependence was actually due to the presence of nickel ion and not an ionic strength effect. Magnesium chloride accelerates the rate slightly, while nickel ion greatly retards the rate of reaction. This effect was studied in greater detail, but solubility requirements necessitated the use of a water-methanol mixed solvent. A solution of 5.5M water in methanol was found to be satisfactory to obtain the necessary solubilities of complex and nickel chloride. 

To establish a good in vitro/in vivo correlation, the composition and ionic strength of the receptor solution must be adjusted. For fentanyl, the best correlation was obtained with a receptor solution comprised of a 10-fold dilution of modified Dulbecco phosphate-buffered saline (without calcium or magnesium) at pH 7.4. The currents tested in vitro ranged from 0 to 400 pA and were applied to a silver anode and a silver chloride cathode using a constant current power supply. The in vitro data presented in Fig. 5 clearly demonstrate the expected linear dependence of fentanyl delivery on current and the excellent correlation to the in vivo data. 

For this and other biological reactions the standard state chosen depends on temperature, the ionic strength, pH of the solution, and the presence of other ions (especially magnesium ions for this reaction). At very low ionic strength, pH = 7, and in the absence of magnesium ions, the values of the standard-state Gibbs energy of reaction,... 

Like the Serratia endonuclease, the enzyme cleaves the 3 0-P bond in DNA. Also like the Serratia endonuclease, the enzyme prefers magnesium over other divalent metal ions. VPpol endonuclease is a domain swapped dimer with 163 amino acids per monomer. In the absence of salt, its kcat/KM appraoches 10. This number is dominated by the Kii/value which is close to 1 x 10 M. The kcat value is highly dependent on ionic strength, but without salt it has been reported to be 0.046 min (39). 

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