Adsorption of 5′-AMP and catalytic synthesis of 5′-ADP onto phosphate surfaces: Correlation to solid matrix structures

Abstract

A non-enzymatic formation of 5'-ADP starting from phosphorylation of 5'-AMP in the presence of either calcium phosphate or calcium pyrophosphate precipitates is reported. This reaction is taken as a model for the study of heterogeneous catalysis of transphosphorylation in prebiotic conditions. Experiments were performed in completely aqueous media and in media containing dimethyl sulfoxide (Me2SO), to simulate periods of dehydration in primitive aquatic environments. It has been observed that the nucleotide is adsorbed onto both calcium phosphate and calcium pyrophosphate in accordance with Langmuir isotherms. Adsorptive capacity and affinity of the precipitates for nucleotide are changed by the presence of Me2SO, suggesting that the interaction between biomonomers and surfaces can be modulated by the degree of hydration of the anionic components of these compounds. In completely aqueous environments, formation of 5'-ADP from 5'-AMP adsorbed on precipitates of calcium phosphate and calcium pyrophosphate is very small. However, in the presence of 60% Me2SO this synthesis increases by factors of 3 and 6 for surfaces of calcium phosphate and calcium pyrophosphate, respectively, and follows first-order kinetics. Determinations of free energy changes show that phosphorylation of 5'-AMP adsorbed to these precipitates is thermodynamically favorable. Depending on the precipitation time of the samples and the composition of the medium, structural analysis of these precipitates by electron and X-ray diffraction shows changes in their cristallinity grade. It is proposed that these changes are responsible for the modulation of the quantity of adsorbed nucleotides to the surface of solid matrices as well as the catalytic activity of the precipitates.

Pyrophosphate and Adenosine 5′-Diphosphate Synthesis from Phospho(enol)pyruvate: Catalysis by Phosphate Minerals and Modulation by Dimethyl Sulfoxide

“…Phosphorolysis of Phospho(enol)pyruvate by a Surface of Calcium Phosphate with Formation of Pyrophosphate: Effects of Dimethyl Sulfoxide on Reaction Rate Figure 1A shows the time course of PPi formation as the result of the phosphorolytic cleavage of PEP adsorbed onto a surface of precipitated Pi.Ca with catalytic properties that simulate ''enzyme-like'' activity (HermesLima and Vieyra 1992;Tessis et al 1995), suspended in purely aqueous medium (≈3 mol solid Pi/ml) or in the presence of 80% (v/v) Me 2 SO (≈5 mol solid Pi/ml). The addition of the cosolvent promotes a two-to threefold increase in reaction rate, and in both conditions the appearance of PPi was linear during the first 5 h of incubation at 37°C.…”

“…As will be demonstrated below, the increase in the rate of PPi synthesis promoted by Me 2 SO can be associated with an increase in the insolubility of the Pi.Ca complex and, consequently, with the amount of the solid matrix with phosphorylating capacity (Tessis et al 1995). Apart from the increase in the available surface, the increased PPi synthesis may be due to Me 2 SOinduced desolvation of the reactant anions PEP and Pi (Parker 1962) or due to modifications in the structural characteristics of the Pi.Ca matrix.…”

“…Apart from the increase in the available surface, the increased PPi synthesis may be due to Me 2 SOinduced desolvation of the reactant anions PEP and Pi (Parker 1962) or due to modifications in the structural characteristics of the Pi.Ca matrix. It has been demonstrated that Me 2 SO promotes a decrease in the average Pi.Ca particle size, in the aggregation of the grains, and in the yield of 5Ј-AMP phosphorylation (Tessis et al 1995).…”

“…The product [ 32 P]PPi was identified by thin-layer chromatography using PEI-cellulose sheets and by specific decomposition using inorganic pyrophosphatase (Vieyra et al 1985;HermesLima and Vieyra 1992). Synthesis of 5Ј-ADP in the absence or presence of Pi.Ca was measured as described elsewhere (Tessis et al 1995). Experimental values represent averages of at least three independent experiments performed in duplicate with different solutions.…”

“…Examples of catalytic processes involving minerals and energy-donor molecules include the formation of pyrophosphate (PPi) (Krane and Glimcher 1962;Miller and Parris 1964;Hermes-Lima and Vieyra 1992;Vieyra et al 1995) and the synthesis of adenosine 5Ј-diphosphate (5Ј-ADP) on the surface of phosphates (Tessis et al 1995).…”