ABSTRACT
Phosphorus is an element fundamental to life and a structural and functional component of all organisms. It has been called the “Devil’s element” (Emsley, 2001) due to its ability to glow in the dark and to produce several highly toxic derivatives. It is found universally in vital cell constituents such as nucleic acids, nucleotides, phosphoproteins, and phospholipids. It occurs in teichoic and teichuronic acids in the walls of Gram-positive bacteria and in phytins (also known as phytates or inositol phosphates) in plants. In many types of bacteria and some yeast, it may also be stored intracellularly as polyphosphate granules. Simple phosphates (orthophosphate) can form anhydrides with other phosphates, as in organic and inorganic pyrophosphates and polyphosphate. Phosphate can also form anhydrides with carboxyl groups of
organic acids, with amino groups of amines, and with sulfate (as in adenosine 5′-phosphosulfate). The phosphate anhydride bond serves to store biochemically useful energy. For example, a standard free energy change ΔG°) of −32 kJ mole−1 is associated with the hydrolysis of the terminal anhydride bond of adenosine 5′-triphosphate (ATP), yielding adenosine 5′-diphosphate (ADP) + Pi. Unlike many anhydrides, some of those involving phosphates such as ATP are unusually resistant to hydrolysis in the aqueous environment (Westheimer, 1987). Chemical hydrolysis of these bonds requires 7 min of heating in dilute acid (e.g., 1 N HCl) at the temperature of boiling water (Lehninger, 1975). At more neutral pH and physiological temperature, signicant hydrolysis proceeds only in the presence of appropriate enzymes (e.g., ATPase). The relative resistance of phosphate anhydride bonds to hydrolysis is attributable to
13.1 Biological Importance of Phosphorus / 265 13.2 Occurrence in the Earth’s Crust / 266 13.3Conversion of Organic into Inorganic Phosphorus and Synthesis of Phosphate Esters / 266 13.4Assimilation of Phosphorus / 267 13.5Microbial Solubilization of Phosphate Minerals / 268 13.6Microbial Phosphate Immobilization / 269
13.6.1Phosphorite Deposition / 269 13.6.1.1Authigenic Formations / 269 13.6.1.2Diagenetic Formation / 271
13.6.2Occurrences of Phosphorite Deposits / 271 13.6.3Deposition of Other Phosphate Minerals / 271
13.7Reduction of Phosphate / 272 13.8Microbial Metabolism of Organophosphorus Compounds / 273 13.9Microbial Oxidation of Inorganic Reduced Forms of Phosphorus / 273 13.10Summary / 274 References / 274
the negative charges on the phosphates at neutral pH (Westheimer, 1987). It is probably the reason why ATP got selected in the evolution of life as a repository and universal transfer agent of chemical energy in biological systems. The instability of phosphoric acid anhydride linkages at high temperatures is one of the key factors that limit life to temperatures below 130°C (White, 1984).
