Inorganic ions divalent cations

Fio. 2. Proposed kinetic model for yeast inorganic pyrophosphatase. Here M represents Mg + but may also apply to any divalent cation with which the enzyme is active. In the rate equation A represents all mono-magnesium PPi complexes, B represents the di-magnesium complex, and I represents free PPi. Hydrogen ion equilibria are not considered. Kinetic runs were done at pH 7.4, 30° (9). Best values for kinetic constants were obtained from a computer program for nonlinear regression (9S). 

Many inorganic compounds have the fluorite and inverse fluorite structures (a) all halides of the larger divalent cations except two fluorides in this class (b) oxides and sulfides of univalent ions (c) oxides of large quadrivalent cations and (d) some intermetallic compounds. Table 10.1.5 lists some compounds of the fluorite and inverse fluorite types and their a parameters. 

A number of inorganic species can be separated by extraction with suitable solvents. For example, a single ether extraction of a 6 M hydrochloric acid solution will cause better than 50% of several ions to be transferred to the organic phase included among these are iron(III), antimony(V), titanium(III), gold(IIl), molybde-num(VI), and tin(IV). Other ions, such as aluminum(IIl) and the divalent cations of cobalt, lead, manganese, and nickel, are not extracted. 

The effects of inorganic salts on plasma cholinesterase (E16) are largely contradictory. Fruentova (F9) reported that divalent cations are more effective inhibitors of horse serum cholinesterase than are monovalent ions, whereas divalent ions are frequently reported to have a marked activating effect (H38, T8, VI). Lithium and sodium nitrates have been shown by in vitro studies of the reaction of human plasma cholinesterase with benzoylcholine to have identical inhibition profiles (W21), while sodium and potassium chlorides had very similar inhibitory actions on the hydrolysis of acetylcholine by human plasma (H47). Silver nitrate, copper sulfate, and mercuric chloride are powerful inhibitors of F. polycolor butyrylcholinesterase (N2). Cohen and Oosterbaum (C12) concluded that activation by cations occurring at the usual substrate concentration is highly dependent on the experimental conditions. This supposition is very relevant to the somewhat random choice of buffers and substrates in the work reported above. 

Martin, C.J. and Evans, W.j. (1 987) Phytic acid divalent cation interactions. V.Titrimetric, calorimetric, and binding studies with cobalt (II) and nickel (II) and their comparison with other metal ions. Journal of Inorganic Biochemistry 30, 101-119. 

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