Magnesium ions bacterial

Bioluminescent reactions are also employed for imaging purposes, in particular the firefly and the bacterial luciferin/luciferase ones (Fig. 1). The firefly luciferin/luciferase reaction requires ATP, magnesium ions, and oxygen. Many different luciferins and mutant luciferases have been investigated to optimize the... 

The glycoside/aminoglycoside antibiotics, like the macrolides, exert a bacteriostatic effect due to selective inhibition of bacterial protein synthesis, with the exception of novobiocin (26). The compounds neomycin (27), spectinomycin (28) and streptomycin (29) bind selectively to the smaller bacterial 30S ribosomal subunit, whilst lincomycin (30) binds to the larger 50S ribosomal subunit (cf. macrolides). Apramycin (31) has ribosomal binding properties, but the exact site is uncertain (B-81MI10802). Novobiocin (26) can inhibit nucleic acid synthesis, and also complexes magnesium ion, which is essential for cell wall stability. 

It is now known that in the bacterial systems the donor is a pair of chlorophyll molecules, the special pair", P, and the initial acceptors is either another chlorophyll molecule, an auxiliary chlorophyll B, or a bacteriopheophytin, H, a chlorophyll molecule in which the central magnesium ion has been replaced by a pair of protons. Although many pigments are present acting as antenna molecules to gather the light, additional chlorophylls are most common. How can the same molecule have such different roles In spite of the fact that the antenna and the RC pair molecules are the same, light is transferred from the antenna to the RC with unit efficiency. 

Dairy and animal products may become rancid by bacterial attack. Calcium and magnesium ions are required for the propagation of the microorganisms and the development of rancidity. If these calcium and magnesium ions are tightly sequestered as phosphate complexes, they are unavailable to the microorganisms. 

As mentioned above, certain metal ions may be necessary for activity or stability. Thus calcium is needed for bacterial a-amylase. Magnesium or cobalt is needed with glucose isomerase. Calcium stabilises the starch-liquifying bacterial a-amylases but inactivates the glucose isomerase that may be used subsequently. Many enzymes contain an additional non-... 

Pyrophosphatases, which are present in all cells, and catalyze hydrolysis of inorganic pyrophosphate (PPj) to orthophosphate (P ) (see Chapter 6, Section D), also drive metabolic sequences. The very active pyrophosphatase of E. coli has a turnover number of over 2 x 104 s 1 at 37°C. The 1000 molecules per cell are sufficient to immediately hydrolyze any pyrophosphate produced by bacterial metabolism.733 The much studied soluble pyrophosphatases of E. coli,7 A 7 ,r yeast,736 and other organisms736ab are metalloenzymes that are most active with Mg2+. Two Mg2+ ions are held, mostly by carboxylate side chains, while a third apparently enters the active site as magnesium pyrophosphate, perhaps MgP20-. As with other metallohydrolases, a metal-bound hydroxyl ion may serve as the attacking nucleophile. 

A schematic view of bacterial photosynthetic reaction centre with a chain of electron-carrying metal prosthetic groups is shown in Figure 11.4. The metal ions involved are magnesium (bacteriochlorophylls) and iron (haem and non-haem iron species). 

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