In enzymatic systems

Cooperative catalysis between multiple metal centers is considered to be common in enzymatic systems,96 and using this idea for designing catalytic systems... 

A vast class of instabilities in enzymatic systems arises from the pH dependence of enzymatic activity. In general, protein molecules contain a number of ionizing groups, such as (—COOH), which can be ionized to give the negatively charged (—COO") ion, and (—NH2), which can add on a proton to give (—NH ). The active enzyme may be represented as in Fig. 4 then addition of acid or base to the active enzyme may be depicted as in Fig. 5, or schematically... 

In contrast to these reaction schemes, enzymatic hydrolysis shows optimal rates at pH 7-8, at least as far as animal esterases are concerned. Increasing concentrations of either H+ or 0H slow the hydrolytic reactions down. Therefore, a different catalytic mechanism, not included in Ingold s reaction schemes, must be operative in enzymatic systems. 

Figure 3.3 a Dynamic adsorption/desorption in heterogeneous catalysis and in enzymatic systems occurs both at active sites and elsewhere on the support b similar coordination/dissociation occurs also in homogeneous complexes. 

The determination of binding constants, K, and inhibitor constants, Ki, for micelle-catalyzed reactions permits at least qualitative interpretations of the effect of substrate structure on the extent and nature of micellar complexation and allows a comparison of the magnitude of the binding constants for substrates in micellar systems with those in enzymatic systems. The hmited quantity of such data available at... 

Examples of rate-promoting motions in enzymatic systems 328... 

Kohen, A. (2005). Probes for hydrogen tunneling and coupled motion in enzymatic systems. In Schowen, R., Klinman, J. and Hynes, J. (eds), Handbook of Hydrogen, Vol. 2 Biological Aspects of Hydrogen Transfer. Wiley, Weinheim... 

Catalytically active soluble chiral metal complexes containing a relatively cheap metal such as Co give interesting enantioselectivity in the hydrogenation of 1,2-diketones . Bio dimethylglyoximato Co(II) 3 (cobaloxime), associated with a cocatalyst and possessing a chiral amine function such as quinine, quinidine, cinchonidine, ephe-drine, brucine, or 5-( - )-a-methylbenzylamine, forms a chiral system that induces preferentially one enantiomer, as in enzymatic systems ... 

Designing derivatives of metal complexes that can form productive complexes with substrates and can manifest high effective molarities toward peptide bonds is not easy. Nature has adopted macromolecular polypeptides as the backbones of enzymes to tune the positions of catalytic elements in enzyme-substrate complexes, and thus, to achieve high effective molarities of the catalytic groups. The idea of macromolecular systems for the catalyst-substrate complexes may be applied not only to a macromolecular catalyst and a small substrate as in enzymatic systems, but also to a small catalyst and a macromolecular substrate. If a protein is used as the substrate, even a small catalyst may form a productive complex by utilizing the three dimensional (3D) structure of the protein substrate (22). 

In order to generate more structurally relevant biomimetics for dinuclear metallohydrolases much effort has been devoted to the synthesis of asymmetric ligands. These ligands are considered to be more suitable models for the asymmetric coordination environment found in enzymatic systems. Nordlander et al. proposed that asymmetric complexes are not only more appropriate functional models for the active site of phosphoesterase enzymes, but also that they exhibit enhanced catalytic rates compared with their symmetric counterparts [1-3]. A selection of ligands used to generate purple acid phosphatase [1, 4, 5, 6-10], phosphoesterase [11], urease [12, 13], catechol oxidase [14] and manganese catalase biomimetics [15, 16] is displayed in Fig. 7.1. 

Xon-biological transfer of amino groups has also been effected between a-amino acids and the carbonyl of or-ketoacylamino acids (Herbst and Shemin, 94) no well-established instance of reactions of this type in enzymatic systems is known as yet. 

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