Wyman

Filling of these cavities with a nonpolar molecules is enthalpy driven. See Diederich, F. Smithrud, D. B. Sanford, E. M. Wyman, T. B. Ferguson, S. B. Carcanague, D. R. Chao, I. Houk, K. N. Acta Chem. Scand. 1992, 46, 205 and references cited therein See (a) Blokzijl, W. Ph. D. Thesis, University of Groningen, 1991 (b) Streefland, L. Ph. D. TTzewis, University of Gronirigen, 1998 and references cited therein. 

A. Bose, J. Lankford, and H. Couque, Development and Characterisation of Mdiabatic Shear Prone Tungsten Heavy Mlloys, Wyman-Gordon Co., Worcester, Mass., SWRI-06-4601, Order No. AD-A270 477, 81 pp.. Avail., NTIS, 1993. 

Thioindigo [522-75-8] M 296.2, m >280 . Adsorbed on silica gel from CCl4/ benzene (3 1), eluted with benzene, crystd from CHCI3 and dried at 60-65°. [Wyman and Erode J Am Chem Soc 73 1487 1951.] This paper also gives details of purification of other thioindigo dyes. 

Edsall, J. T., and Wyman, J., 1958. Carbon dioxide and carbonic acid, in Biophysical Chemistry, Vol. 1, Chap. 10. New York Academic Press. 

In 1965, Jacques Monod, Jeffries Wyman, and Jean-Pierre Changeux proposed a theoretical model of allosteric transitions based on the observation that allosteric proteins are oligomers. They suggested that allosteric proteins can exist in (at least) two conformational states, designated R, signifying relaxed, and T, or taut, and that, in each protein molecule, all of the subunits have the same conformation (either R or T). That is, molecular symmetry is conserved. Molecules of mixed conformation (having subunits of both R and T states) are not allowed by this model. 

FIGURE 15.9 Monod-Wyman-Changeux (MWC) model for allosteric transitions. Consider a dimeric protein that can exist in either of two conformational states, R or T. Each subunit in the dimer has a binding site for substrate S and an allosteric effector site, F. The promoters are symmetrically related to one another in the protein, and symmetry is conserved regardless of the conformational state of the protein. The different states of the protein, with or without bound ligand, are linked to one another through the various equilibria. Thus, the relative population of protein molecules in the R or T state is a function of these equilibria and the concentration of the various ligands, substrate (S), and effectors (which bind at f- or Fj ). As [S] is increased, the T/R equilibrium shifts in favor of an increased proportion of R-conformers in the total population (that is, more protein molecules in the R conformational state). 

FIGURE 15.12 71 versus [S] curves for an allosteric V system. The V system fits the model of Moiiod, Wyman, and Chaiigeux, given the following conditions (1) R and T have the affinity for the substrate, S. (2) The effectors A and I have different affinities for R and T and thus can shift the relative T/R distribution. (That is, A and I change the apparent value of L.) Assume as before that A binds only to the R state and I binds only to the T state. (3) R and T differ in their catalytic ability. Assume that R is the enzymatically active form, whereas T is inactive. Because A perturbs the T/R equilibrium in favor of more R, A increases the apparent Vmax- I favors transition to the inactive T state. 

Glycogen phosphorylase conforms to the Monod-Wyman-Changeux model of allosteric transitions, with the active form of the enzyme designated the R state and the inactive form denoted as the T state (Figure 15.17). Thus, AMP promotes the conversion to the active R state, whereas ATP, glucose-6-P, and caffeine favor conversion to the inactive T state. 

First draw both Lineweaver-Burk plots and Hanes-Woolf plots for the following a Monod-Wyman-Changeux allosteric K enzyme system, showing separate curves for the kinetic response in (1) the absence of any effectors (2) the presence of allosteric activator A and (3) the presence of allosteric inhibitor I. Then draw a similar set of curves for a Monod-Wyman-Changeux allosteric Uenzyme system. 

In the Monod-Wyman-Changeux model for allosteric regulation, what values of L and relative affinities of R and T for A will lead activator A to exhibit positive homotropic effects (That is, under what conditions will the binding of A enhance further A-binding, in the same manner that S-binding shows positive coop-... 

Monod, J., Wyman, J., and Changenx, J.-R, 1965. On die nature of allo.steric tran.sitions A plan.sible mo(. Journal of Molecular Biology 12 88-118. The cla.ssic paper diat provided the first theoretical analysis of allo.steric regulation. 

Because this enzyme catalyzes the committed step in fatty acid biosynthesis, it is carefully regulated. Palmitoyl-CoA, the final product of fatty acid biosynthesis, shifts the equilibrium toward the inactive protomers, whereas citrate, an important allosteric activator of this enzyme, shifts the equilibrium toward the active polymeric form of the enzyme. Acetyl-CoA carboxylase shows the kinetic behavior of a Monod-Wyman-Changeux V-system allosteric enzyme (Chapter 15). 

The results obtained by measuring the affinity to oxygen in the presence of various monohydric alcohols (methanol, ethanol, 2-propanol, 1-propanol) 140-144> were interpreted in terms of the Monod-Wyman-Changeux model145), by which the change of the standard free-energy difference between R and T state in the absence of oxygen, due to the addition of alcohol, can be determined, i.e. 

Table 9 gives the values of AG and AGn calculated according to Wyman s theory. 

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