Amino acid covalently attached, effect

Some physical and functional properties of casein modified by the covalent attachment of amino acids are given in Table IX. Despite extensive modification, the relative viscosities of 2% solutions of the modified proteins did not change significantly, with the exception of aspartyl casein which was more viscous. There was some decrease in the solubilities of aspartyl casein and tryptophyl casein as compared with the casein control. It is anticipated that adding some 11.4 tryptophyl residues per mole of casein would decrease the aqueous solubility of the modified protein. However the results with aspartyl casein are unexpected. The changes in viscosity, solubility, and fluorescence indicate that aspartyl casein is likely to be a more extended molecule than the casein control. There was a marked decrease in the fluorescence of aspartyl casein and tryptophyl casein (see Table IX). The ratios of the fluorescences of acetylmethionyl casein to methionyl casein and t-BOC-tryptophyl casein to tryptophan casein were 1.20 and 2.01, respectively, indicating the major effects that these acyl groups have on the structure of the casein. 

In recent years, a small number of new phases have become available that are more suited to CEC. Phase Separations (Deeside. UK) have produced a SCX stationary phase. This is a strong cation-exchange material which contains aminopropyl-derivatised silica that has sulphonic acid groups covalently attached to the amino end of a short alkyl chain. The sulphonic acid groups are effectively ionised at all working pHs due to their low p/faS. Fig. 4.5 shows the dependence of EOF on pH of the mobile phase for a capillary packed with Phase Separations SCX stationary phase. The EOF is almost the same over the whole range. It increases beyond pH 7, presumably due to the added ionisation of the surface silanols. 

Short-term regulation of the activity of the three above-mentioned enzymes is achieved by either allosteric effectors (such as intermediates in the carbohydrate converting pathways, energy-rieh phosphates and related compounds, and ions) or covalent alterations of the enzyme under consideration. Allosteric effects are achieved when binding of an effector molecule to the enzyme results in structural changes in the catalytic center and, hence, alteration of the biological activity of the enzyme. The effectors themselves do not bind to the catalytic center, but to distant sites of the protein. Covalent alteration of enzymatic activity is commonly achieved by covalent attachment of a phosphate group to one or more amino acid... 

The isolated TE domain from the tyrocidine (tyc) NRPS has recently been shown to catalyze the macrocyclization of unnatural substrates to generate a variety of cyclic peptides. In conjunction with standard solid-phase peptide synthesis, Walsh and coworkers demonstrated a broad substrate tolerance for peptidyl-N-acetylcysteamine thioesters by the tyrocidine TE [41,42], Cyclization of peptide analogs, where individual amino acids were replaced with ethylene glycol units, was observed with high efficiency. In addition, hydroxyacid starter units were readily cyclized by the isolated TE domain to form nonribosomal peptide-derived macrolactones. More recently, Walsh and coworkers have demonstrated effective cyclization of PEGA resin-bound peptide/polyketide hybrids by the tyrocidine TE domain [43], Utilization of a pantetheine mimic for covalent attachment of small molecules to the resin, serves as an appropriate recognition domain for the enzyme. As peptide macrocyclizations remain challenging in the absence of enzymatic assistance, this approach promises facile construction of previously unattainable structures. 

To overcome this problem, PAMAM dendrimers have been modified and/ or used at lower generations. Skoza and colleagues covalently attached GALA, a 30 amino acid synthetic peptide, with a glutamic acid-alanine-leucine-alanine repeat, to PAMAM dendrimers and observed that the transfection efficiency was enhanced. In another approach, PAMAM dendrimers were covalently linked with cyclodextrin macrocycles to create a synergic effect between dendrimer and cyclodextrin. To enhance PAMAM transport into cells, a series of artificial proteins were designed by... 

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