Binding, geometry random

Why did nature use an Fe-S cluster to catalyze this reaction, when an enzyme such as fumarase can catalyze the same type of chemistry in the absence of any metals or other cofactors One speculation would be that since aconitase must catalyze both hydrations and dehydrations, and bind substrate in two orientations, Fe in the comer of a cubane cluster may provide the proper coordination geometry and electronics to do all of these reactions. Another possibility is that the cluster interconversion is utilized in vivo to regulate enzyme activity, and thus, help control cellular levels of citrate. A third, but less likely, explanation is that during evolution an ancestral Fe-S protein, whose primary function was electron transfer, gained the ability to catalyze the aconitase reaction through random mutation. 

The end product of the MIP production process, in the vast majority of cases, is a fine powder containing a population of vacant binding sites with a small proportion of non-recoverable template trapped deep within the particle matrix. For monolithic polymers binding sites are of two basic types internal and external. External sites are the product of random cleavage of the cage structure of the total 3-dimensional site. Their geometry depends upon the orientation of the cavity constituents relative to the fracture plane. These are believed to contribute only a small amount of the total binding... 

Given only an arbitrary conformation of an SDM monomer, a bisinterca-lated DNA model, and the constraints above, distance geometry produces 10-15 families of structures from 100 random trials after clustering. Binding models fall into two major classes ... 

Some recent papers report on the metal ion binding at homo- and copolymers of maleic acid a) Insoluble polymer metal complexes have been prepared from Cu(II), Co(II), Ni(II) and Zn(II) with poly(maleic acid) in water. For Ni(II) and Co(II) complexes a distorted octahedral symmetry has been proposed (see Section 5.4, Experiment 5-5) [39]. b) The kinetics and equilibrium of the complexation of Al(III) with a random copolymer of maleic acid and acrylic acid has been studied [40]. In the first step of complexation an outer sphere complex is formed, followed in the second rate-determining step by the formation of an inner sphere complex, c) Insoluble complexes have been obtained from poly(maleic acid-co-olefin) with Cu(II), Co(II), Ni(II) and Zn(II) [41], For the Zn(II) complexes a distorted octahedral geometry has been proposed. 

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