Phosphate metallic hydroxy

Aminoacyl adenylates (296), which are formed from protein amino acids and ATP, act as acylating agents towards t-RNAs, acylating their terminal 3 -hydroxy groups. These charged tRNAs are then used in protein synthesis. Little is known about the reactivity of aminoacyl adenylates (296), and studies are now reported of a model compound, alanyl ethyl phosphate (297). As expected, hydrolysis in both acid and base involves attack at the C=0 group of (297) with departure of ethyl phosphate. Metal ions (Cu +, Zn +) were found to act as catalysts of the hydrolysis. 

Phosphate pigments other than zinc and aluminium phosphates have received much less attention in the technical literature. This group includes phosphates, hydroxy-phosphates, and acid phosphates of the metals iron, barium, chromium, cadmium. 

Due to mechanistic requirements, most of these enzymes are quite specific for the nucleophilic component, which most often is dihydroxyacetone phosphate (DHAP, 3-hydroxy-2-ox-opropyl phosphate) or pyruvate (2-oxopropanoate), while they allow a reasonable variation of the electrophile, which usually is an aldehyde. Activation of the donor substrate by stereospecific deprotonation is either achieved via imine/enamine formation (type 1 aldolases) or via transition metal ion induced enolization (type 2 aldolases mostly Zn2 )2. The approach of the aldol acceptor occurs stereospecifically following an overall retention mechanism, while facial differentiation of the aldehyde is responsible for the relative stereoselectivity. 

Enzyme catalysed racemisation is an attractive method. The enzymes are known as racemases and they often need cofactois like pyrodoxyl phosphate (PEP) or bivalent metal ions to function properly. The snbstrates used in racemisation reactions have two features in common, i) the stereocentre carries a proton, ii) adjacent to the stereocentre is a carbonyl gronp or another function that make the proton at the stereocentre acidic. Most racemases work on amino acids and df-hydroxy acids. The principle of those needing PEP is formation of a Schiffs base between the aldehyde of PEP and the amino group of the amino acid (like in Figure 2.6). 

Hydroxy groups on benzene rings can be replaced by NH groups if they are first converted to aryl diethyl phosphates. Treatment of these with KNH and potassium metal in liquid... 

Pyridoxal 5 -phosphate is an essential cofactor for many enzymes responsible for the metabolic conversions of amino acids. The fourth step in its synthetic pathway in Escherichia coli is catalyzed by the divalent metal ion-dependent enzyme 4-hydroxythreonine-4-phosphate dehydrogenase (PdxA), which converts 4-hydroxy-l-threonine phosphate (HTP) to 3-amino-2-oxopropyl phosphate. The... 

Figure 1 Chemical mechanism of DNA polymerase and 3 -5 exonuclease, (a) DNA polymerase reaction. The enzyme chelates two metal Ions using three aspartic acid residues (only two are shown). Metal ion A abstracts the 3 hydroxyl proton of the primer terminus to generate a nucleophile that attacks the a-phosphate of an incoming dNTP substrate. The phosphoryl transfer results In production of a pyrophosphate leaving group, which is stabilized by metal Ion B. (b) The 3 -5 exonuclease proofreading activity is located in a site that is distinct from the polymerase site yet it uses two-metal-ion chemistry similar to DNA synthesis. The reaction type is hydrolysis in which metal ion A activates water to form the hydroxy anion nucleophile. Nucleophile attack on the phosphate of the mismatched nucleotide releases it as dNMP (dGMP in the case shown).

The exposure of sulfide minerals contained in mine wastes to atmospheric oxygen results in the oxidation of these minerals. The oxidation reactions are accelerated by the catalytic effects of iron hydrolysis and sulfide-oxidizing bacteria. The oxidation of sulfide minerals results in the depletion of minerals in the mine waste, and the release of H, SO4, Fe(II), and other metals to the water flowing through the wastes. The most abundant solid-phase products of the reactions are typically ferric oxyhydroxide or hydroxysulfate minerals. Other secondary metal sulfate, hydroxide, hydroxy sulfate, carbonate, arsenate, and phosphate precipitates also form. These secondary phases limit the concentrations of dissolved metals released from mine wastes. 

A connective synthesis of alkynes inspired by the Julia alkenation was developed by Lythgoe and coworkers for the synthesis of la-hydroxy vitamin D3, as shown in Scheme 34. The P-keto sulfone (101) derived by condensation of the the metalated sulfone (99) with the ester (100) was converted to the enol phosphate (102), which on reductive elimination gave the enynene (103). 

Thermal decomposition is the process wherein the structure of the catalyst is formed by the heat treatment of the precursor after volatile components are decomposed or chemical water associated with the lattice structure of the solid is removed. Examples of such a phenomenon are the decomposition of metal nitrate, hydroxide, carbonate, chloride, sulfate, phosphate, hydroxy salts, or oxy salts to corresponding oxides. The following equation shows the decomposition of cobalt nitrate coupling with partial oxidation of Co ... 

Significant work has been done in Japan on liquid and vapor phase oxidation of p-cresol. Similarly Professors Sheldon and Jihad Dakka of Delft University of Technology, Holland have reported use of metal alumino-phosphate sieves (MeAPos) more particularly, CoAPO, for selective oxidation to p-hydroxy benzaldehyde with molecular oxygen in alkaline methanolic solution at 50°C [33]. 

The isomerisation of aldoses and ketoses by hydride transfer, although suggested for enzymic isomerisations of aldoses and ketoses (rather than their phosphates), and having precedent in the metal ion-catalysed isomerisations of ot-hydroxy ketones, was considered to be the less common route until the paradigmal aldose-ketose isomerisation, that of glyceraldehyde to dihydrox-yacetone, was examined by NMR spectroscopy. Identification and analysis of all products of the reaction in D2O permitted concentrations to be chosen which minimised side-reactions. A useful feature of the system was that it was possible to integrate the areas of proton resonances in the CHD and CH2... 

Butlerov found out that in alkaline medium (calcium hydroxide), formaldehyde HCHO polymerizes to form about 20 different sugars as racemic mixtures, Butlerov 1861. The reaction requires a divalent metal ion. Breslow found a detailed mechanism of reaction that explains the reaction products, (Breslow 1959). He found that glycol-aldehyde is the first product that is subsequently converted into glyceral-dehyde (a triose), di-hydroxy-acetone, and then into various other sugars, tetrose, pentose, and hexose. The formose reaction advances in an autocatalytic way in which the reaction product is itself the catalyst for that reaction with a long induction period. The intermediary steps proceed via aldol and retro-aldol condensations and, in addition, keto-enol tautomerizations. It remains unexplained how the phosphorylation of 3-glyceraldehyde leads to glycral-3-phosphate (Fig. 3.6). Future work should study whether or not ribozymes exist that can carry out this reaction in a stereo-specific way. 

A similar chelation of metal to enzyme-bound substrate may also contribute to enzyme catalysis of proton transfer at carbon. For example, X-ray crystallographic analysis of complexes bet veen 3-keto-L-gulonate 6-phosphate decarboxylase and analogs of the 1,2-enediolate reaction intermediate provide evidence that the essential magnesium dication is stabilized by coordination to both the C-2 oxygen and the nonreacting C-3 hydroxy of the reaction intermediate [88]. 

Rudnick and Abeles purified proline racemase to 95% homogeneity from Clostridium sticklandii, and characterized it 92. The enzyme is composed of two identical subunits with a molecular weight of about 38000, and is independent of any cofactors or metals. Most amino acid racemases require pyridoxal 5 -phosphate, which labilizes the bond between the a-hydrogen and the chiral center by aldimine formation with the a-amino group of the substrate. However, PLP is not involved in the reaction of proline racemase acting on an a-imino acid. The enzyme also acts on 2-hydroxy-L-proline and 2-allo-hydroxy-D-proline although slowly they are epimer-ized at a rate of 2 and 5% of the rate of L-proline racemization, respectively. L-Proline and D-proline showed Km values of 2.9 and 2.5 mti, respectively1119. ... 

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