Mella Paecht-Horowitz

Polycondensation of amino acid phosphoanhydrides: III. Polycondensation of alanyl adenylate

Abstract This paper reports an investigation on the behavior of alanyl adenylate in aqueous solution. It has been found that the mixed anhydride undergoes a relatively slow hydrolysis in the acidic pH range, whilst it polymerizes rapidly to give peptides at pH values higher than 7. The hydrolysis in the acidic range obeys a simple first-order reaction, and the hydrolytic constants can be determined directly from the kinetic run. In the basic range where there are two competitive reactions, hydrolysis and polymerization, evaluation of the constants for both reactions has been carried out by applying formulae derived by Katchalsky and Ailam in Part I of this series. It has been found that both the hydrolytic and polymerization constants increase with the pH. A correlation has been found between the polymerization constants of alanine, or its peptides, and their respective p K value. This correlation indicates that the reacting groups are the unionized amino groups of the amino acid moieties.

Polycondensation of amino acid phosphoanhydrides: II. Polymerization of proline adenylate at constant phosphoanhydride concentration

Abstract This study is devoted to the polymerization of proline adenylate to oligopeptides. The polymerization was carried out at pH 8.5 maintaining a steady-state concentration of the active phosphate. It was found that every degree of polymerization reaches a steady concentration after a relaxation time increasing with the degree of polymerization. From the time dependence of the concentrations and the steady level it was possible to evaluate the hydrolytic constant k h = 0.1 min −1 and the polymerization constant for dimer formation k 1 = 3.65 l · mole −1 ·min −1 , for trimer formation k 2 = 5.4 l · mol −1 · min −1 , for tetramer k 3 = 8.8 l · mole −1 · min −1 and for the pentamer k 4 = 10.7 l · mole −1 · min −1 . For higher degrees of polymerization the constants approach an approximately equal k value. Alternative runs of polymerization with different yields could be obtained by adding free proline to the solution of phosphoanhydride. All the results follow the same theoretical description and can be adequately represented by the same set of rate constants.

Synthesis of amino acyl-adenylates under prebiotic conditions.

SummaryIn a system containing zeolites, ATP and amino acids, amino acid-ADP anhydrides are able to form in an aqueous medium at neutral pH and room temperature. When montmorillonite, a clay possessing swelling properties, is added, polypeptides are formed. It is suggested that this may be the mechanism whereby prebiotic synthesis of peptides took place.

The mechanism of clay catalyzed polymerization of amino acid adenylates

Amino acid adenylates were adsorbed on montmorillonite when either the interspatial faces or the edges of the latter were blocked. By this method it could be observed that adsorption of the amino acid adenylates takes place mostly on the planes of the clay. However, for polymerization to take place, the edges of the clay have to be free as well and apparently only these molecules polymerize which are attached to the planes of the clay by their amino groups and to the edges of the clay by their phosphate group. Thus all the charges of the molecules which might produce their repulsion from each other would be neutralized. As a consequence of these attachments polymerization on the clay would take place on its planar sites, but only on those neighboring its edges. The question whether neutralization of charges is also the reason why biochemical substrates have to attach themselves by several points to enzymes and thus make biochemistry fit into the framework of general chemistry, is raised.

The Possible Role of Clays in Prebiotic Peptide Synthesis

Hypotheses of macromolecule formations during the prebiotic era are described. The presumed role of minerals and clays in these reactions are: concentration of monomers, proton release by ion exchange whenever the reaction demands it, scattering of the charges of the interacting substances, thus allowing such substances to interact, which in the absence of clays repel each other due to their charges. Because of these reasons the polymerization mechanism in the presence of clays is different from that in their absence. While in the absence of clays only free amino acids or peptides can interact with active amino acid anhydrides, giving thus peptides increased by only one unit, in the presence of clays two molecules of amino acid anhydrides can interact, giving a still active peptide anhydride which can interact with another active peptide. Clays catalyze polymerization only in these cases where the amino acid is small enough to enter between the sheets of the clay. Apparently most of the reactions also occur there and not on the surface of the clay. Copolymerization of different pairs of amino acids proceeds selectively in the presence of clay. The relationship between this selecitvity and prebiotic parent proteins is discussed.

Clays as possible catalysts for peptide formation in the prebiotic era

From the point of view of prebiotic synthesis, clays might have performed functions of concentration, catalysis, and protection of molecules.The degrees of polymerization obtained, when amino acid adenylates are added to montmorillonite suspensions in water, are much higher than those obtained by polymerization in the absence of such a clay. In addition, they are of a discrete spectrum, usually multiplies of 6 or 7, and reach values of up to 40 mers. In the absence of clay a continuous spectrum of degrees of polymerization is obtained, and usually up to 4–6 mers only. Copolymerization in the absence of clays yields mostly random copolymers, in their presence mostly block copolymers are obtained.Optical density measurements show that after adsorption has taken place on the clay, stacking of its layers occurs. Polymerization starts only after these stacked layers have been formed. The distances between the layers — as measured by X-rays — increase during polymerization, probably because the resulting polymers settle in their interspace, while the adsorption site of the active monomers is at the edges of the clay.

Polycondensation of amino acid phosphoanhydrides

Abstract A mathematical theory for the polycondensation of amino acid phosphoanhydrides is presented. The basic assumption is that the phosphoanhydride reacts primarily with free amino acid formed in hydrolysis or added from outside. The growth of the polymeric chains is based on the interaction of free peptides with amino acid phosphoanhydride. The mathematical framework enables the evaluation of the hydrolytic constants as well as the propagation constants for different degrees of polymerization. Various initial conditions were considered. Cases of special interest fully developed were (a) the case when all propagation constants are equal, as generally found at alkaline pH, and (b) the case in which the concentration of active amino acid is maintained constant during polymerization by suitable supply from outside.

The influence of various cations on the catalytic properties of clays

SummaryPolymerization of alanine adenylate in the presence of various clays in their Na form gave increasing degrees of polymerization in the following order: montmorillonite < nontronite < hectorite. With montmorillonite, presaturated with different cations the order was: Mg < Ca < Fe < Al < Na. From all these clays, hectorite was the only one to enable also some polymerization of lysine.

Polymerization of alanine in the presence of a non-swelling montmorillonite.

SummaryAlanine, starting from alanine-adenylate, has been polymerized in the presence of non-swelling Al-montmorillonite. The yield of polymerization is much lower than that obtained in the presence of swelling Na-montmorillonite. The possibility that the changing interlayer spacing in Na-montmorillonite might be responsible for its catalytic properties, is discussed.

Micelles and Solid Surfaces as Amino Acid Polymerization Propagators

In many of his papers and treatises, Oparin advanced the hypothesis that the formation of biomacromolecules from biomonomers might have taken place inside coacervates (1), droplets consisting of polymers separating out from a solution in which a monomer polymerizes in the presence of another polymer. When the new polymer reaches a certain size, phase separation, accompanied by a sharp shift towards synthesis (2), takes place. Evreinova et al. have shown that monomers of the surrounding medium can concentrate inside such coacervates up to a hundred-fold, depending on the type of the polymer forming the coacervate and on the nature of the monomers in the solution (3). These experiments led Oparin to the idea that coacervates were the means of concentration of monomers from dilute solutions and that polymerization takes place inside them.