Transformation of Inactive

In lay language, activation means making an object or a person active. A number of fields of science and engineering have adopted this term to describe various processes and phenomena (e.g. regeneration of inorganic catalyst, transformation of inactive enzyme to an active form, excitation by heating or irradiation) [1]. In... 

Figure 4.14 EXAFS Fourier transforms of inactive and active forms of trime-thylamine M-oxide reductase. Transforms show both experimental data (solid lines) and best fits (broken lines), and are Mo-S phase-corrected, computed over the A -range 0.1-14.5 A. Schematic structures of each form are also shown adjacent to the transforms.

Deficiency in coenzyme, resulting from a lack of vitamins, for instance, may decrease the concentration of the respective enzyme (Kaplan, 1966). According to Levy s hypothesis (Levy et al., 1966), the coenzymes might also influence the active structure of the enzyme molecule. Indeed, most of the enzymes probably react in polymeric form. Levy observed, for example, that NADP favors transformation of inactive glucose-6-phosphate dehydrogenase into a more active and highly polymerized form. 

It is established by biotesting that complexation and adsor ption ar e the most important processes promoting transformation of metal compounds in biologically and the chemically inactive forms and essential decrease their toxicity. The kinetics data have shown the maximal decrease in toxicity was observed in natural water where the complexation occurred with participation of both DOM and added HS. 

There are also important requirements for the heterogeneous catalysts (i) the catalyst should not hinder the formation of the [substrate - modifier] complex, (ii) the modifier should not adsorb irreversible onto the catalyst (iii) the catalyst should be inactive in the transformation of the modifier into a new derivative, (iv) the catalyst should be resistant towards poisoning by modifier, substrate or product. 

There are two possible approaches for the preparation of optically active products by chemical transformation of optically inactive starting materials kinetic resolution and asymmetric synthesis [44,87], For both types of reactions there is one principle in order to make an optically active compound we need another optically active compound. A kinetic resolution depends on the fact that two enantiomers of a racemate react at different rates with a chiral reagent or catalyst. Accordingly, an asymmetric synthesis involves the creation of an asymmetric center that occurs by chiral discrimination of equivalent groups in an achiral starting material. This can be done either by enan-tioselective (which involves the reaction of a prochiral molecule with a chiral substance) or diastereoselective (which involves the preferential formation of a single diastereomer by the creation of a new asymmetric center in a chiral molecule) synthesis. 

Which are the possible approaches for the preparation of optically active products by chemical transformation of optically inactive starting materials ... 

Tyrosine is a precursor of thyroid hormones as well as L-dopa. Both thyroxine and L-dopa are employed in clinical medicine thyroxine to treat hypothyroid patients and L-dopa to treat patients with Parkinsonism. L-dopa is also the precursor to the pigment of the skin known as melanin. The enzyme that catalyzes the transformation of tyrosine into L-dopa, tyrosine hydroxylase, also catalyzes the transformation of L-dopa into melanin. Albinism is a genetic disease in which a mutation in the gene encoding tyrosine hydroxylase results in an inactive enzyme. People with albinism have no pigment in their skin, hair, or retina. 

Purine Antimetabolites. Purine synthesis can be blocked by 6-mercaptopurine (7.77) and 6-thioguanine (7.78). Both require conversion to the mononucleotide in a lethal synthesis —a mechanism distinguished from the formation of suicide substrates in that the enzyme that transforms the inactive pro-dmg to the active inhibitor is different from the enzyme that is being blocked. inhibitors are formed and bound by the same... 

Fig. 2.12. Structural changes at the N-terminus of glycogen phosphorylase as a result of phosphorylation. a) R-form of the dimer of glycogen phosphorylase a. b) T form of the dimer of glycogen phosphorylase b. Phosphorylation at Serl3 near the N-terminus transforms the inactive glycogen phosphorylase b into the active glycogen phosphorylase a. The N-terminus rearranges significantly as a result of phosphorylation. In the inactive T-state the N-terminus interacts with the same subunit, while in the R-form it forms interactions with the other subunit. After Barford and Johnson (1991), with permission.

If we transform the MO s such that condition (5 11) is fulfilled, the resulting transition density matrix will be obtained in a mixed basis, and can subsequently be transformed to any preferred basis The generators Epq of course have to be redefined in terms of the bi-orthonormal basis, but this is a technical detail which we do not have to worry about as long as we understand the relation between (5 9) and the Slater rules. How can a transformation to a bi-orthonormal basis be carried out We assume that the two sets of MO s are expanded in the same AO basis set. We also assume that the two CASSCF wave functions have been obtained with the same number of inactive and active orbitals, that is, the same configurational space is used. Let us call the two matrices that transform the original non-orthonormal MO s [Pg.242]

Manufacture and Processing. Although fermentation procedures have not been reported, assumptions concerning fermentation media and optimal conditions have been made. The transformation of the biologically inactive rifamycin B to the biologically active rifamycin S is usually accomplished chemically. Several rifamycin B oxidases have been isolated that can enzymatically transform rifamycin B to rifamycin O, which is hydrolyzed in the fermentation medium to rifamycin S. The enzymes from Monocilliim spp. ATC 20621 and Humicold spp. ATCC 20620 are intracellular, whereas... 

In spite of its close similarity to methylcyclopropane, methyloxirane exhibits different behavior. The observed maximum curve means that the kink sites are inactive sites in the transformation of oxiranes. The reason for the inactivity is not completely clear, but it is very probable that CO poisoning is responsible. 

Schematic diagrams of the amino acid sequences of chymotrypsin, trypsin, and elastase. Each circle represents one amino acid. Amino acid residues that are identical in all three proteins are in solid color. The three proteins are of different lengths but have been aligned to maximize the correspondence of the amino acid sequences. All of the sequences are numbered according to the sequence in chymotrypsin. Long connections between nonadjacent residues represent disulfide bonds. Locations of the catalytically important histidine, aspartate, and serine residues are marked. The links that are cleaved to transform the inactive zymogens to the active enzymes are indicated by parenthesis marks. After chymotrypsinogen is cut between residues 15 and 16 by trypsin and is thus transformed into an active protease, it proceeds to digest itself at the additional sites that are indicated these secondary cuts have only minor effects on the enzymes s catalytic activity. (Illustration copyright by Irving Geis. Reprinted by permission.)...

Despite the presence of sites that strongly chemisorb a variety of molecules, pure silica gel is catalytically inactive for skeletal transformations of hydrocarbons. However, as has recently been emphasized by West et al. (79), only trace amounts of acid-producing impurities such as aluminum need be present in pure silica gel to provide catalytic activity— especially when a facile reaction such as olefin isomerization is used as a test reaction. They found that addition of 0.012% Al to silica gel resulted in a 10,000-fold increase in the rate of hexene-1 isomerization at 100°C over the pure gel. An earlier study by Tamele et al. (22) showed that introduction of 0.01% wt Al in silica gel produces a 40-fold increase in cumene conversion when this hydrocarbon is cracked at 500°C. The more highly acidic solids that are formed when substantial concentrations of metal oxides are incorporated with silica are discussed in following sections. 

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