Interconverting systems

Covalent interconversion of enzymes is well established as a fundamental theme in metabolic regulation. The prototypic reversible interconverting systems include the sequence of phosphorylation/dephosphorylation steps in the activation of mammalian glycogen phosphorylase and pyruvate dehydrogenase as well as the nucleotidyla-tion/denucleotidylation using UTP and ATP in the bacterial glutamine synthetase cascade (see Fig. 1.). 

Equations 18.14 and 18.17 (or 18.15 and 18.19) are kinetically equivalent (Chapter 2, section F) the rate of formation of N by both pathways follows a rate constant multiplied by the concentration of C, the dominant species in solution. Thus, the rate constant for formation of N reports back simply on the difference in structural properties between the transition state for the formation of N and the ground state that is C. This means that we cannot determine whether the reaction is U — C — N or C U — N by kinetics. The physical reason for this is that we are examining what is, in effect, a rapidly interconverting system of U and C that is being slowly converted to N that is,... 

Abraham and co-workers17 have pointed out an interesting test that may be used in the case of binary interconverting systems. For such systems... 

Such surface structure should be realized as a rapidly interconverting system, at least, between the above-mentioned two forms as described by Eq. (7), although the relative proportions of these forms vary depending upon the environmental factors such as temperature, pH, ionic strength, etc. It is also pointed out that such a conformational change illustrated in Fig. 17 might be related to the consequence of the conformational switch responsible for proton uptake after the release of a proton from the extracellular surface in the photocycles. This view is obviously consistent... 

In passive ion-transport studies (entries 1-3 in Table IV), the KT -transport to the basic OUT aqueous phase was much faster than that to the acidic one. This means that trans-l(n=10) can transport K+ more efficiently than interconvertible systems. Photoirradiation enhanced the rate by 2.1-fold that is, the photoinduced ammonium-biting is useful as a tool to facilitate the ion-release from the membrane phase to the acidic OUT aqueous phase. 

The most stable nuclear configuration of this system is a pair of H2 molecules. There are three possible spin coupling combinations for H4 corresponding to three distinct stable product H2 pairs H1 H2 with H3 H4, H1 H3 with H2 H4, and H1 H4 with H2 H3. Each H atom contributes one electron, the dot diagrams indicate spin pairing. The three combinations are designated as Hfl), HOT), and H(III), respectively. They may be interconverted via square transition states, Figure 2. 

A number of reaction products have been isolated from the (Tj -C H )2TiCl —N2—reductant system, where n = 1, 2, all of which assume an intense blue color in solution. Spectroscopic absorption occurs at a maximum, of ca 600 nm. The relationship among these products is unclear (185,186), but the labihty of the ring maybe an important complicating factor. When (Tj -C R 2TiCl2 [11136-36-0] R = CH3, is used, two distinct interconvertible... 

The photochemical behavior of the isomeric 3-methyl-2-phenyl-2-allyl-l-azirine (66) system was also studied. Irradiation of (66) in cyclohexane gave a quantitative yield of azabicyclohexenes (67) and (68). Control experiments showed that (65) and (66) were not interconverted by a Cope reaction under the photolytic conditions. Photocycloaddition of (66) with an added dipolarophile afforded a different 1,3-dipolar cycloadduct from that obtained from (65). The thermodynamically less favored endo isomer (68b) was also formed as the exclusive product from the irradiation of azirine (66b). 

Amino-l,2,4-triazole undergoes a cyclocondensation with 3-etlioxyacrolein (7) to form 1,2,4-triazolo[l,5-a]pyrimidine (3) or its [4,3-u] isomer (5), according to whether it reacts as IH or 4H tautomer 2 or 4. Moreover, the pyrimidines 3 and 5 can interconvert by a Dimroth rearrangement. Since the H NMR spectrum 30a does not enable a clear distinction to be made AMX systems for... 

Alkyl derivatives of 1,3-butadiene usually undergo photosensitized Z-E isomerism when photosensitizers that can supply at least 60 kcal/mol are used. Two conformers of the diene, the s-Z and s-E, exist in equilibrium, so there are two nonidentical ground states from which excitation can occur. Two triplet excited states that do not readily interconvert are derived from the s-E and s-Z conformers. Theoretical calculations suggest that at their energy minimum the excited states of conjugated dienes can be described as an alkyl radical and an orthogonal allyl system called an allylmethylene diradical ... 

Heat, like work, is energy in transit and is not a function of the state of a system. Heat and work are interconvertible. A steam engine is an example of a machine designed to convert heat into work.h The turning of a paddle wheel in a tank of water to produce heat from friction represents the reverse process, the conversion of work into heat. 

The choice of vx is a matter of convenience for the system of interest. Table 1 summarizes the various definitions of vx and corresponding, /Y, commonly in use [3], The various diffusion coefficients listed in Table 1 are interconvertible, and formulas have been derived. For polymer-solvent systems, the volume average velocity, vv, is generally used, resulting in the simplest form of Jx,i- Assuming that this vv = 0, implying that the volume of the system does not change, the equation of continuity reduces to the common form of Fick s second law. In one dimension, this is... 

Dt and the mutual diffusion coefficient, D, are interconvertible by correcting for the penetrant activity in the polymer [12], For highly concentrated systems where the penetrant volume fraction, < >, is low,/can be approximated by... 

Oligomerization of nucleobases can be advantageous to reinforce the H-bonding supramolecular motifs when supramacromolecular polymers are desired. Moreover the different interconverting outputs that may form by oligomerization define a dynamic polyfunctional diversity which may be extracted selectively under the intrinsic stability of the system or by interaction with external factors by polymerization in the solid state. 

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