Catalytic advantages

For further discussion and for calibration purposes we will have to define a reference solution reaction which would be sufficiently related to the given enzymatic reaction. This will help us in removing the problems associated with concentration effect and in focusing on the actual catalytic advantage of the enzyme. To do this we describe the reference reaction in solution as... 

The acidic function of single zirconium phosphonate showed rather poor catalytic activities for hydrolysis of ethylacetate in aqueous solutions. In addition, over Zr(03PCH2S03H)2 catalyst, the reaction proceeds as a homogeneous reaction, even though the catalytic activity is higher than other acidic zirconium phosphonates. The objective of this study is to explore the role of a second phosphonate function in single crystal phase on the catalytic performance of acidic function and hydrophobic function of zirconium phosphonates and to learn how to exploit this second function to achieve a catalytic advantage in certain applications. 

The catalytic advantage of an intramolecular reaction over its intermolecular counterpart is due to entropy. The intermolecular reaction involves two or more molecules associating to form one. This leads to an increase in order and a consequent loss of entropy. An effective concentration may be calculated from... 

In the last section we showed that enzymes have evolved to bind the transition states of substrates more strongly than the substrates themselves. It will now be seen that it is catalytically advantageous to bind substrates weakly. 

We have discussed in general terms the catalytic advantages of enzyme-transition state complementarity combined with high KM s, and have seen that this combina-... 

Besides having a noncovalent association of subunits as in tryptophan synthase, some enzymes are double-headed, in that they contain two distinct activities in a single polypeptide chain. A good example of this is the indole 3-glycerol phosphate-synthase-phosphoribosyl anthranilate isomerase bifunc-tional enzyme from the tryptophan operon of E. coli. The crystal structure of the complex has been solved at 2.0 A resolution.39 The two enzymes have been separated by genetic manipulation.40 The activity of the two separate monomeric monofunctional constituents is the same as in the covalent complex so there is no catalytic advantage of having the proteins fused. 

A detailed understanding of the properties of early transition metal carbides is of practical importance because they often demonstrate unique catalytic advantages over their parent metals in activity, selectivity and resistance to poisoning.1,2 We have chosen vanadium carbide films, produced on a vanadium (110) single crystal surface, as model systems to understand the fundamental aspects related to the electronic and catalytic properties of carbide materials. One of the main advantages of using the single crystal surface is that it enables one to apply powerful surface science spectroscopies to determine the electronic and catalytic modifications... 

A question of particular interest concerns the catalytic advantage that a selenol in the active site of an enzyme has in comparison to a thiol group. It has been approached by replacing the selenocysteine in the formate dehydrogenase Ft by a cysteine residue and by determining the catalytic parameters of the Se-wild-type species with the mutant S-species. Table 1 presents the data obtained. They show that koit of the Se enzyme is more than 300-fold higher than that of the S variant and that the affinity to the substrate is only marginally affected. Similar replacements of selenocysteine by cysteine in other enzymes like the deiodinase type 1 or methionine sulfoxide reductase B corroborated these results. 

Warshel, A. and Papazyan, A. (1996). Energy considerations show that low-barrier hydrogen bonds do not offer a catalytic advantage over ordinary hydrogen bonds. Proc. Natl. Acad. Sci. USA 93, 13665-13670... 

One of the most powerful mechanistic techniques is the design and synthesis of models which will demonstrate a particular mechanistic hypothesis making use of such deviations. As an example of this technique we shall consider a proposed mechanism of serine proteases. Bruice and his co-workers devised a chemical modeP of the catalytic triadhyTpothQsis (Scheme 1) which was advanced to explain the catalytic advantage of serine proteases. 

It is unclear, however, if the operation of the catalytic triad imparts any catalytic advantage. This was investigated in a systematic study of human leukocyte elastase [14, 42]. For p-nitroanilides of substrates R-Val-, R-Pro-Val-, R-Ala-Pro-Val-, and R-... 

The pyridinium ring in PLP provides a highly optimized electron sink for stabilizing the pair of electrons released by the decarboxylation step. Consequently, the decarboxylation step is irreversible. Beginning the reaction with a Schiff base, rather than with a free aldehyde, also provides an additional catalytic advantage (705), as Schiff base interchange is faster than formation of a Schiff base from an aldehyde and an amine. Precise conformational control is also an... 

The observations of low effective concentrations in intramolecular general acid-base-catalysed reactions may be extrapolated to determine the catalytic advantage of having a general acid or base catalyst as part of the protein structure in enzyme-catalysed reactions. The catalytic advantage appears to be minimal. Although it may be necessary for the proton acceptor or donor to be at the active site, as the equivalent intermolecular catalyst may be sterically prevented from reaching... 

In this sense, the micropores alford preparative and catalytic advantages for encapsulated metal clusters over the conventional surface-grafted metal clusters. Regardless of the treatment and prevailing conditions that may involve several cyclic sequence of oxidation, reduction with H2 and catalytic carbonylation with CO/H2, in the microporous environment retains cluster unity and even at higher temperatures sintering is prevented. 

Abstract Recent developments in the use of N-heterocyclic carbenes (NHC) as ligands in palladium-mediated transformations are described. These versatile ligands afford steric and electronic control of the metal environment, just as tertiary phosphines, yet they also allow synthetic access and operational catalytic advantages compared to metal-tertiary phosphine-centered transformations. 

E. (2009) Substrate channelling in an engineered bifunctional aldolase/kinase enzyme confers catalytic advantage for C-C bond formation. Chem. Commun. (Camb.), 1721-1723. 

We had predicted earlier that considering the protein and water content of stroma there is a possibility that RuBP carboxylase might be existing as a multienzyme complex (6,7,8), Later this finding was confirmed by Gontero et al (9) who showed that five enzymes of Calvin cycle exist as multienzyme complex. We have also observed that, the association of RuBP carboxylase with phosphoribulokinase and phospho-riboisomerase offers a catalytic advantage to RuBP carboxylase (8),... 

Polymer-bound microheterogeneous catalytic systems have a number of catalytic advantages first they are relatively easy to fabricate second the functions of catalysis and electron transport between the support surface and the catalytic site are distinct and third there is a three-dimensional dispersion of active sites throughout the polymer host matrix. A high local concentration of catalytic sites can be achieved even though the total quantity of active material is small. This dispersion of catalytic material offers important catalytic advantage indeed highly... 

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