Cross-catalysis

Yao, S., Ghosh, I., and Chmielewski, J. (1998). Selective ampliflcation by auto- and cross-catalysis in a replicating peptide system. Nature, 396, 447-50. 

If there is a racemizing cross-catalysis (Eq. 5) with k 2, the trajectory equation is rewritten as ... 

The library was designed not to contain amino acids that could be self-acylated, thus Ser, Thr, Lys, and Cys were not part of the library. His was incorporated as a known weak acylation catalyst and was expected to be selected. After reacting the library with the dye-marked Pfp ester, and thorough washing, several beads remained red, indicating covalent attachment of the dye to the resin beads. Analysis of the peptides on these red beads showed that each active bead carried at least one His. There is, therefore, no cross catalysis between different beads. The method can be used to search for catalysts of any bimolecular reaction in which one reaction partner can be attached to a solid support and the other labeled with a dye, a fluorophore, or radioactivity. 

Fig. 2 (A)Self-replication versus (B) cross-catalysis, according to von Kiedrowski et al (Ref. [19]). A. A. B. B stands for oligomeric fragments that can combine to form the templates (AA, AB BB ). (View this art in color at www.dekker.com.)...

Self-replication can occur through autocatalysis with a self-complementary template (Fig. 2A) or by cross-catalysis with a complementary template (Fig. 2B). In the latter case, two complementary units catalyze each other s formation. This is significant as modern DNA is made up of two complementary strands that replicate in a cross-catalytic manner. Studies on a simple nonenzyinatic DNA system capable of competing auto- and crosscatalysis. show that in the absence of an initial template, both pathways are equally as likely, but that in the presence of a seeding template, the cross-catalytic route is more efficient. 

In quite a few cases, chaos can be predicted based on appropriate mathematical model (Lorenz or Rosselor) (Chapter 12). The strange attractor obtained in such cases signifies Deterministic Chaos . Such models exhibit cross-catalysis and inhibition. Experimentally observed deterministic chaos can be easily ascertained using definite criteria, although prediction of complex time order is quite difficult in many cases. In terms of causality principle, the complexity in the system arises due to complex interdependence of a number of causes and effects. 

The behavior of synthetic replication networks has been studied using several different chentical systems such as DNA, RNA, proteins, and small molecules. These simple networks are formed by simultaneous implementation of autocatalysis and cross-catalysis. This evolves the formation of reciprocal catalysis in binary systems and more complex functions in large networks. In the main body of this review, we focus on peptide-based synthetic networks thus, other recently developed replication networks are only discussed shortly in the following paragraphs. 

Simulating autocatalysis and cross-catalysis within the networks... 

We have recently suggested a general formal mechanism that accounts for the kinetics of networks that perform multiple autocatalysis and cross-catalysis using (7 and 8). In this description, the dimers T T are the only catalyt-ically active species. Each of the reactants E, combines directly with only one reactant of type N (like in our original network experiment) to form the templates T, either in the slow background reaction or in a catalyzed reaction. This analysis can easily be extended to include as many E, species as needed, as well as several reactants of type N. 

In a following study, a four component peptide network, capable of autocatalysis and cross-catalysis, allowed selective amplification of one or more of the products by changing the reaction conditions.This system carried the ability to selectively amplify one or more product molecules in response to changes in pH or salt concentration. 

Polymers and their additives should be paired in such a manner as to exclude their cross-catalysis and cross-propagation... 

In their modeling of unsaturated polyester resin formation, Beigzadeh et al. [100] and Zetterlund et al. [101] have also found the Chen-Wu relationship more useful than the rather cumbersome empirical models of Paatero et al. [102] or Leh-tonen et al. [103]. Zetterlund et al. [101] have also presented interesting experimental data on the simultaneous self- and cross-catalysis by two carboxyl groups, namely those formed by the addition of maleic and phthalic anhydride to 1,2-propanediol they show there is an anti-synergistic effect that is, the total rate reaction of the two carboxyl groups is lower than the sum of the rates of reaction of the individual acids with the same concentration and at the same temperature. 

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