Magnesium react with proteins

There are problems as well in the absorption of certain drugs in the presence of specific food components. L-Dopa absorption may be inhibited in the presence of certain amino acids formed from the digestion of proteins [43], The absorption of tetracycline is reduced by calcium salts present in dairy foods and by several other cations, including magnesium and aluminum [115-117], which are often present in antacid preparations. In addition, iron and zinc have been shown to reduce tetracycline absorption [118], Figure 17 illustrates several of these interactions. These cations react with tetracycline to form a water-in-soluble and nonabsorbable complex. Obviously, these offending materials should not be co-administered with tetracycline antibiotics. 

Generally, sodium and potassium react only to a limited extent with proteins, whereas calcium and magnesium are somewhat more reactive. Transition metals, e.g., ions of Cu, Fe, Hg, and Ag, react readily with proteins, many forming stable complexes with thiol groups. Calcium cations and ferrous, cupric, and magnesium cations may be integral parts of certain protein molecules or molecular associations. Their removal by dialysis or sequestration appreciably lowers the stability of the protein structure toward heat and proteases. 

When the sarcoplasmic calcium transport system operates in the reverse mode and synthesizes ATP from ADP and inorganic phosphate during calcium release, inorganic phosphate reacts with the transport protein also leading to the formation of a phosphoprotein [115 -117]. This reaction also requires ionized magnesium but is suppressed when the concentration of ionized calcium in the medium exceeds 10 /xM. In the transport protein of the sodium-potassium system, analogous cation dependent phosphoryl transfer reactions take place. It is difficult, however, to directly correlate phosphorylation and ion movement in these membranes. 

Solid-phase chemistry Magnesium is released from protein, and penetrates the layers of the slide to react with a formazan dye. Calciiun is bound to a chelating agent to prevent interference. Accuracy was less satisfactory with control sera than with native sera. 

Another phase of protein synthesis in which I became interested at Yale is peptide-chain initiation. In 1966, J. Eisenstadt and I proved that the chain initiator fMet-tRNAf is strictly required for the translation of f2 bacteriophage RNA, a natural messenger RNA in a crude extract from E. coli. This requirement was, however, only manifested when the magnesium ion concentration in the extract was low. For this demonstration, we had to deplete the pool, and block the formation, of fMet-tRNAf in the extract. We found two compounds which accomplished this by making formyltetrahydrofolate, the source of the formyl residue in fMet-tRNA(, unavailable trimethoprim, an inhibitor of dihydrofolate reductase, and hydroxylamine which was shown by Bertino to react with methylenetetra-hydrofolate and thereby deplete the pool of formyltetrahydrofolate, produced the result desired. 

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