JTW's Evolutionary Origins - Author: Wachtershauser, Gunter

Phosphorylation in a Chemoautotrophic Surface Metabolism

The Role of Phosphates in Metabolism

"Phosphate groups play a central role in all extant metabolisms. Westheimer (1987) has rationalized this role by a hypothetical entrance of phosphate into a 'prebiotic chemistry' owing to a selective advantage of the chemical reactivity of phosphate esters; while Davis (1958) stressed the function of preventing leakage through the cell membrane."
[Wachtershauser, 1992, pp. 136]

Phosphates Assist in Surface Bonding to the Pyrite Surface

"...the theory of a pyrite pulled surface metabolism suggests that the first function of phosphate esters was that of surface bonding to a cationic mineral surface (Wachtershauser 1988d) With phosphate groups as surface-bonding mediators, the surface metabolism can include constituents (e.g. sugars, glycerol lipids, serine) which by themselves are not surface bonders."
[Wachtershauser, 1992, pp. 136]

The Insolubility of Phosphates in Solution

"The early ocean must have contained a high concentration of polyvalent metal ions, notably Mg²⁺, Ca²⁺, and Fe²⁺. The insolubility of the phosphates of these metal ions and, as a consequence, the low abundance of dissolved phosphate ions poses a major difficulty for all versions of the prebiotic broth theory. It is hard to understand how phosphorylated organic compounds can form in a broth, scavenged of soluble phosphate by the omnipresent metal ions, and how any brothborne 'RNA organism' could survive for long under conditions of phosphate starvation. In the auto-origin approach, this problem finds a simple solution. Insoluble ferrous phosphate (vivianite) will necessarily liberate phosphate ions by its conversion to pyrite. Moreover, phosphate ions are strong anionic surface bonders and their bonding to the surfaces of iron sulfides and pyrite will compete with the precipitation of insoluble phosphates. This means a high abundance of phosphate ions within the surface metabolism. Since the first function of phosphorylation is that of surface-bonding mediation, such phosphorylation can occur without having the phosphate ions pass through a fully solvated and surface detached state."
[Wachtershauser, 1992, pp. 136]

"Since a pyrite-pulled chemo-autotrophic origin of life produces surface-bonding carboxylate groups directly by CO2-fixation, it has been concluded that surface metabolists with only thiolate and carboxylate surface bonding groups (Carboxypeds) are the first organsims and that surface metabolists with additional phosphate surface bonding (Phosphorypeds) are of a later vintage (Wachtershauser 1988d). The fact that most extant branch pathways of the RCC have phosphate groups entering late (E1) seems to bear this out:"
[Wachtershauser, 1992, pp. 136]

Evolutionary Relation #1 [pp.122] (Florkin, 1944,1974)

Terminal Extension:

(--->A-^b->B) ==> (--->A-^b->B-^c->C)

Historic Relation #11 [pp. 136]

Pathways With Non-phosphorylated Constituents ==> Pathways With Phosphoylated Constituents
[Wachtershauser, 1992, pp.94]

"...projecting from the insolubility of Fe₃(PO₄)₂ (vivianite) and FePO₄H, but not FePO₄H₂),
we may expect biochemical constituents with at least one phosphate monoester group (-O-PO₃^2-),
as in phosphorylated sugars, or with at least two phosphate diester groups (-O-PO₂^-~O-) to form strong bonds to a pyrite surface."
[Wachtershauser, 1992, pp. 94]

"...vacant pyrite surfaces may become occupied by the metabolist and more importantly non-pyrite crystals such as iron sulphide or other ferrous minerals, notably FeCO₃ (siderite) or Fe(PO₄)₂ (vivianite) may become colonized, with a subsequent metabolically promoted conversion into pyrite, where by the mineral base provides the ionic nutrients of Fe²⁺ and PO₄^3-. All polyanionic constituents are particularly stong surface bonders."
[Wachtershauser, 1992, pp. 96]

Historic Relation #10

Thiol to Alcohol or Phosphorylation -C-SH ==> -C-OH or -C-O-PO3^2-
[Wachtershauser, 1992, pp. 133]

"In extant metabolisms phosphate groups are found attached to carbon atoms with four different oxidation states:

• To C⁴⁺ in carbamyl-phosphate (H₂N-CO-O-PO^32-)or in carboxly-phosphate (HO-CO-O-PO₃^2-), the intermediate in the formation of carboxy-biotin (Knowles, 1989; Kluger, 1989).
• To C³⁺ in acylphosphates (R-CO-O-PO₃^2-).
• To C²⁺ in PEP (CH₂=C(COOH)-O-PO₃^2-).
• To C¹⁺, e.g. in phosphorylated sugars.

It has been suggested that C¹⁺ -phosphorylation [the last option on the list] may have originated reductively (Wachtershauser, 1990a). THERE IS, HOWEVER, NO SUPPORT FOR SUCH A PHOSPHORYLATION IN EXTANT METABOLISMS."
[Wachtershauser, 1992, pp. 136-137]

"All extant substrate level phosphorylation occurs by converting thioesters into acylphosphates. This is the reason for de Duve's (1988b) proposal for an origin of phosphate acquisition by the phosphorolytic attack of phosphate ions on thioesters, giving rise to the first acylphosphates (R-CO-O-PO₃^2-) and subsequently to polyphosphates (e.g. R-O-P₂O₆^3-). These activated phosphate groups are seen by de Duve as invading the metabolism by phosphoryl transfer, first based mainly on inorganic polyphosphates, and later, on organic polyphosphates such as ATP. This proposal, made in the context of a prebiotic broth theory, suffered however from a lack of a plausible process of thioester formation. Having shown here how thioesters could arise by a pyrite-pulled process (see section III.3.c), we can now adopt and incorporate de Duve's proposal into the theory of a pyrite-pulled origin."
[Wachtershauser, 1992, pp. 137]

"It has recently been shown (Yamagata et. al. 1991) that volcanic gases contain P₄O₁₀ which hydrolyzes in liquid water to produce polyphosphates. This finding is of interest for the theory of a pyrite-pulled chemoautotrophic origin of life which has H₂S-rich volcanic exhalations as its primary geochemical setting. It opens up the possibility that phosphoanhydride activation arises first, giving rise to thioester activation by thiolysis. Alternatively, it makes room for the separate appearance of phosphoanhydride activation and of thioester activation in different chemical species, followed by symbiosis."
[Wachtershauser, 1992, pp. 137]

"With the abandonment of pyrite formation in the course of evolution, the metabolism becomes wholly dependent on group activation, first by thioesterification and/or phosphorylation by volcanic polyphosphates; and later by a variety of transactivation processes: [1.] transthiolation [2.] transthioesterification [3.] thioester phosphorolysis [4.] transphosphorylation. This entire repertoire is still in use in extant metabolisms."
[Wachtershauser, 1992, pp. 137]

• Wachtershauser, Gunter
  • Groundworks for an Evolutionary Biochemistry: The Iron-Sulphur World
  • Progress in Biophysics and Molecular Biology: Vol. 58, No. 2, pp.85-202
  • 1992
  • [Pubmed]

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