Acetyl phosphate stability

Gutsche et al. observed that a lipophilic dioxime (the ligand in 4) accelerates by a factor of 60 to 140 the hydrolysis of acetyl phosphate in the presence of an equimolar amount of metal (M = Cu, Zn, Ni) under comicellar conditions with cetyl trimethylammonium bromide (CTAB) at pH 11.5 [22], The hydrolysis reaction was followed by pseudo-first-order kinetics at [ligand] = [M] = 2.5 mM and [CTAB] = 250 mM. Although a possible complex 4 was proposed to exist in the hydroxamate form, there were no experimental data for the stability and structure of metal complexes at pH 11.5 (e.g., it is not known whether the... 

Table II gives approximate stability data for a variety of metabolites and coenzymes. It can be seen that for short (<10 min) assays at 95°, of the compounds listed only NAD (and including NADP, NADH, NADPH) and acetyl phosphate will be degraded at a rate that renders assay results useless, but losses of ATP and ADP may be as high as 20%. The situation is further complicated by the influence of reaction conditions on metabolite/coenzyme stability. For example, ATP stability is greatly affected by pH and metal ions," and NADH stability is very pH sensitive. ...

This novel enzyme was the only esterase able to release acetyl from sugar beet pectin and removed about 30% of the total acetyl groups present. It also caused the release of acetyl groups from a range of other acetylated substrates, either synthetic or extracted from plants, in small amounts. PAE had an apparent molecular weight of 60 kDa and showed optimal activity at pH 5.5 and a temperature of 50 C. The enzyme is sensitive to buffer composition and requires a bivalent cation for optimal activity and stability. In purified form this enzyme proved unstable, especially in phosphate buffers. 

Remove unreacted N-acetyl homocysteine thiolactone and reaction by-products by gel filtration or dialysis against lOmM sodium phosphate, 0.15M NaCl, lOmM EDTA, pH 7.2. Other buffers suitable for individual protein stability may be used as desired. For the silver nitrate-containing reaction, removal of the silver-thiourea complex may be done by adsorption onto Dowex 50, and the protein subsequently eluted from the resin by 1M thiourea. Removal of the thiourea then may be done by gel filtration or dialysis. 

Wu, Y, Seib, P. A. (1990). Acetylated and hydroxypropylated distarch phosphates from waxy barley paste properties and freeze-thaw stability. Cereal Chem., 67, 202-208. 

The structures of the native enzyme and its complexes with several inhibitors have since been obtained at higher resolution in other laboratories, to afford a more complete description of the enzyme - substrate interactions.191 Particularly noteworthy are the lysine residues 7,41, and 66. That these are an important part of the catalytic machinery has been deduced from their conservation in evolution (they have been found in all homologous ribonucleases that have been sequenced), and from their loss of activity when they are acetylated. Lys-41 is particularly important. The lysine side chains are very mobile in the free enzyme, but their mobilities are much decreased on the binding of nucleotide substrate analogues. Lys-41 interacts directly with the phosphate moiety and is thought to stabilize the pentacovalent intermediate. Another residue that has been con-... 

Acetylated wheat distarch phosphate pastes had improved clarity and better storage stability than the pastes of unmodified and crosslinked alone starches when 1% aqueous dispersions were heated in a boiling water bath for 30 minutes and stored at two different temperatures (4°C and 25°C) for 9 days.27 Storage at 4°C of 5% pastes of native and crosslinked wheat starch revealed that both were unstable after one day, the soft texture of the initial pastes being transformed into an opaque and rigid gel that exhibited syneresis. In contrast, the acetylated distarch phosphate was stable for at least... 

Landin M, Perez-Marcos B, Casalderrey M, et al. Chemical stability of acetyl salicylic acid in tablets prepared with different commercial brands of dicalcium phosphate dihydrate. Int J Pharm 1994 107 247-249. 

As catalysts for this reaction, inorganic acids having low volatility and high stability at the temperatures necessary may be used. Phosphoric acid or phosphates, boric acid, boric anhydride or borates may be used either in the molten state, supported on inert carriers, or as the solid salts.108 The use of excess amounts of carbon monoxide and high pressure are specified. Thus, when one volume of methyl chloride and 8 volumes of carbon monoxide are passed, as a mixture, over sodium metaphosphate on pumice at 700° to 800° C. a conversion to 10 or 15 per cent of acetyl chloride is obtained. The use of pressure enables much higher yields to be obtained. 

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