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Phosphate Chemistry Part 1: Fine-Tuned for Life

By Guest Writer - May 4, 2018
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By: Barrie Winn

Phosphates don’t get any respect. At least it seems that way from the generally negative attitude toward phosphates displayed on household products bearing the proud claim “Contains No Phosphate” and in state regulations banning phosphates from fertilizers.1 Of course, these labels and regulations came about as a result of phosphate’s life-stimulating properties: high levels in water bodies will promote algae blooms, which ultimately deplete oxygen. Nevertheless, while regulating the use of phosphates one shouldn’t forget the critical role they play in all living organisms. In fact, human civilization would not be here without them.


Praising Phosphates

Researcher H. Catherine W. Skinner extols phosphates’ unique properties in vertebrates in an article entitled “In Praise of Phosphates, or Why Vertebrates Chose Apatite to Mineralize Their Skeletal Elements.”2 This paper highlights several features of apatite, the calcium phosphate mineral that provides strength to the bones and teeth of vertebrates, which render it ideal for this purpose. The author builds on an earlier paper by F. H. Westheimer entitled “Why Nature Chose Phosphates,”3 which describes the features of phosphates that make them uniquely suited as components of key biomolecules—in particular the information molecules DNA and RNA and the energy molecule ATP (adenosine triphosphate). Westheimer summarizes:

Phosphate esters and anhydrides dominate the living world. . . . Phosphoric acid is specially adapted for its role in nucleic acids because it can link two nucleotides and still ionize; the resulting negative charge serves both to stabilize the diesters against hydrolysis and to retain the molecules within a lipid membrane. A similar explanation for stability and retention also holds for phosphates that are intermediary metabolites and for phosphates that serve as energy sources. Phosphates with multiple negative charges can react by way of the monomeric metaphosphate ion PO3- as an intermediate. No other residue appears to fulfill the multiple roles of phosphate in biochemistry.4

The phraseology used in the titles of both papers is worth a moment’s reflection. “Why Vertebrates Chose . . . ” and “Why Nature Chose . . . ” are phrases which imply the activity of an intelligent agent. While the authors were no doubt thinking within a naturalistic framework wherein “chose” implies “natural selection,” there is no account of how this chemical evolution could have occurred. Regarding the use of apatite, Skinner simply summarizes: “It seems obvious why nature chose this particular calcium phosphate species for its higher biologic forms.”5 While recognizing why phosphates are uniquely suited for living organisms, there is no explanation as to how they could have been “chosen.”


Suitable for Life

Ultimately, phosphate’s unique suitability for living organisms is based on the properties of phosphorus and oxygen atoms, and of the properties of the ions—such as orthophosphate and metaphosphate—that they form. These properties depend on the fundamental structure of matter, and rank among multiple examples of the fine-tuning of the universe that permit the existence of advanced life. One such example includes the unique properties of the water molecule.6

The naturalist might argue that regardless of the fundamental properties of the universe, chemical evolution still had to “choose” phosphates over an alternative chemistry. Some have suggested that alternative life-forms based on arsenic rather than phosphorus could have evolved. The reasoning goes that since arsenic is in the same group of the periodic table as phosphorus, there could be arsenate analogs of phosphate-based biomolecules. This possibility has been explored by studying bacteria that can tolerate high concentrations of arsenic. It was discovered that the bacteria discriminate between the nearly identical phosphate and arsenate ions, with its transport proteins showing a “4,000-fold preference for phosphate over arsenate.”7 This discrimination enables the bacteria to reject arsenate and incorporate phosphate into its biomolecules. One of the researchers said “that he was shocked by how good the proteins were at discriminating between the essential phosphate and the deadly arsenate. This does not mean that arsenate does not get into the bacteria, he points out. ‘It just shows that this bacterium has evolved to extract phosphate under almost all circumstances.’”8 This result of microbial evolution lends support to the claim that phosphates are uniquely suitable for the biomolecules necessary for life.

Skinner discusses the important role apatite plays in the global phosphorus cycle, citing work that “demonstrated that phosphate released from microbes induces apatite formation in close proximity to metabolizing bacterial cells.”9 She goes on to describe how apatite in banded iron formations was found to be associated with carbonaceous material that suggested a biological source and that the “accumulation of phosphate by living forms that produce carbonaceous molecules and that on death become localized as the calcium phosphate mineral apatite, is a pairing that probably goes back to the earliest history of life on Earth.”10 This is thought to be one explanation for the origin of sedimentary phosphate deposits, although Skinner acknowledges: “the actual sources and requisite amounts of phosphate needed to build up these remarkable deposits is not yet known.”11 (This issue will be discussed in part 2 of this article.)


Phosphate Provision Points to Creation

The development of human civilization required a supply of available phosphate for plant nutrition. For centuries this need was provided by readily available life sources (e.g., bones), but as the world population increased over the past century, more substantial supplies were needed. This demand has been met by the vast sedimentary, igneous, and island phosphate deposits that have been discovered on six continents.12 This provision points to the preparation of the earth for human civilization. In fact, “In the past 100 years, phosphate has been discovered at a rate . . . that exceeds the rate of consumption.”13

As we consider the unique features of phosphate that are critical to the stability and function of the information and energy molecules of all living organisms, and the fact that there are sufficient deposits of phosphate to supply the needs of human civilization, we should indeed be prompted to praise. However, Christians believe that, rather than praising phosphate (the creation), we should praise the Creator!14

Endnotes
  1. Kristen L. Miller, “State Laws Banning Phosphate Fertilizer Use,” Connecticut General Assembly OLR Research Report, February 1, 2012; accessed May 12, 2017, https://www.cga.ct.gov/2012/rpt/2012-R-0076.htm.
  2. H. Catherine W. Skinner, “In Praise of Phosphates, or Why Vertebrates Chose Apatite to Mineralize Their Skeletal Elements,” in Frontiers in Geochemistry: Organic, Solution, and Ore Deposit Geochemistry, Konrad Krauskopf vol. 2, int’l book series, vol. 6, W. G. Ernst, ed. (Columbia, MD: Bellwether Publishing, Ltd, 2002), 41–49.
  3. F. H. Westheimer, “Why Nature Chose Phosphates,” Science 235 (March 6, 1987): 1173–78.
  4. Westheimer, “Why Nature Chose Phosphates,” 1173.
  5. Skinner, “In Praise of Phosphates,” 48.
  6. Jeff Zweerink, “Life Hinges on Water’s Competing Quantum Properties,” Today’s New Reason to Believe (blog), Reasons to Believe, March 1, 2013, http://reasons.org/explore/blogs/todays-new-reason-to-believe/read/tnrtb/2013/03/01/life-hinges-on-water-s-competing-quantum-properties.
  7. Daniel Cressey, “‘Arsenic-life’ Bacterium Prefers Phosphorus after All” Nature, October 3, 2012, accessed May 12, 2017, doi:10.1038/nature.2012.11520.
  8. Cressey, “‘Arsenic-Life’ Bacterium.”
  9. Skinner, “In Praise of Phosphates,” 42–43.
  10. Skinner, “In Praise of Phosphates,” 43.
  11. Skinner, “In Praise of Phosphates,” 43.
  12. F. Zapata and R. N. Roy, eds., Use of Phosphate Rocks for Sustainable Agriculture (Rome: Food and Agriculture Organization of the United Nations, 2004), 11–15.
  13. R. P. Sheldon, “Industrial Minerals, with Emphasis on Phosphate Rock,” in Resources and World Development, ed. D. J. McLaren and B. J. Skinner (New York: John Wiley & Sons Limited, 1987), 347–61, quoted in F. Zapata and R. N. Roy, 15.
  14. Romans 1:25.

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