Amino residues

Additional evidence that a dynamic equilibrium exists between an enamine, N-hemiacetal, and aminal has been presented by Marchese (41). It should be noted that no acid catalysts were used in the reactions of aldehydes and amines discussed thus far. The piperidino enamine of 2-ethylhexanal (0.125 mole), morpholine (0.375 mole), and p-toluene-sulfonic acid (1.25 x 10 mole) diluted with benzene to 500 ml were refluxed for 5 hr. At the end of this time the enamine mixture was analyzed by vapor-phase chromatography, which revealed that exchange of the amino residue had occurred in a ratio of eight morpholine to one piperidine. Marchese proposed a scheme [Eqs. (4), (5) and (6)] to account for these... 

We succeeded in showing that recycling of the enzyme was indeed possible in our IL solvent system, though the reaction rate gradually dropped with repetition of the reaction process. Since vinyl acetate was used as acyl donor, acetaldehyde was produced hy the hpase-catalyzed transesterification. It is well known that acetaldehyde acts as an inhibitor of enzymes because it forms a Schiff base with amino residue in the enzyme. However, due to the very volatile nature of acetaldehyde, it easily escapes from the reaction mixture and therefore has no inhibitory action on the lipase. However, this drop in reactivity was assumed to be caused by the inhibitory action of acetaldehyde oligomer which had accumulated in the [bmim][PFg] solvent system. In fact, it was confirmed that the reaction was inhibited by addition of acetaldehyde trimer. =... 

The chelate formation in lithium complexes 17 or 20 contributes to stabilization. Enhancement of kinetic acidity arises from the formation of pre-complexes 16 and 19, respectively. Here, already a dipole is induced and, in addition, proton exchange can proceed intramolecularly via a five- or six-membered ring. Despite these favourable features, the acidity of alkyl carbamates 15 is lower than those of the 1-proton in butane n-BuLi does not lead to deprotonation. In order to suppress carbonyl attack, a branched amino residue NR2 such as diisopropylamino (in Cb) or 2,2,4,4-tetramethyl-l,3-oxazolidin-3-yl (in Cby) is essential. A study on the carbenoid nature of compounds 17 was undertaken by Boche and coworkers. ... 

Figure 4.3 Schematic representation of a 7-transmembrane receptor, exemplified with the human neurokinin-1 receptor (hNK,) The extracellular elements of the receptor are shown in the upper part the amino-acid chain ends with a free amino-residue (NH2) and is called the amino-terminal of the receptor. The longer amino acid chain of the intracellular part (lower part) ends with a free acid-residue (COOH) and is called the carboxylic end. The seven transmembrane domains are lined up within the box, which represents the membrane...

The statistical weight for amino acid residue / is unity if it is not in a helical state. Its statistical weight is os if it initiates a sequence of helical amino residues and s if it propagates an existing helix. 

A commercially packed h.p.l.c. column (25 cm x 4.6 mm) of y-aminopropyl silanised silica [e.g. 5/mi Spherisorb (Regis Chemical Co.), or 7/im Zorbax (Dupont Co.), or 10 /im Lithosorb (Merck), or 5 m irregular (J. T. Baker Chemical Co.)] was sequentially treated, at a pumping rate of 2 ml/min, with the following solutions 2 ml of triethylamine in 40 ml of dry tetrahydrofuran, 2g of (R)-JV-(3,5-dinitrobenzoyl)phenylglycine in 40 ml of dry tetrahydrofuran, 20 ml of dry tetrahydrofuran, and finally 10 per cent propan-2-ol in hexane, until the base line stabilises. The chiral amino acid derivative (which is available from Aldrich Chemical Co.) becomes ionically bonded to the amino residues on the stationary phase. 

Figure 6 Consensus structure of azaphilones for CETP inhibition (A) and hypothetical mechanism of reaction of sclerotiorin with e-amino residue of lysine (B).

The above methods were utilized to conjugate a carboxyl group on a hapten to an amino residue on a protein. Obviously, the above reactions could be, and have been, utilized to conjugate an amino residue on a hapten to the carboxyl residues on proteins. However, there are additional methods which have proven useful for conjugating amine containing haptens to proteins. ... 

Changes in the number of free amino residues alter the modified proteins susceptibility to proteolysis. Albumin chlorination and /V-chloramine formation decreases susceptibility to trypsin digestion. Removing of chloramine residues by treatment with thiosulfate shows that chlorination alters albumin properties by a biphasic mode the reversible chlorination and removal of chloramine moieties markedly increases albumin susceptibility to proteolysis, whereas chlorination produces the irreversible loss of amino moieties and carbonyl group formation effects decrease in albumin susceptibility to trypsin digestion. The effect is related to the number of lost amino residues. A similar relationship was observed for IgG. Fibrinogen and protamine, on the other hand, did not show dependence between chlorination and proneness to trypsin proteolysis (06). 

Trypsin attacks the peptide bonds following the basic amino acids arginine and lysine. Formation of chloramines decrease trypsin binding sites, which causes a decrease in protein susceptibility to trypsin digestion. On the other hand, chloramine formation from free amino residues may induce changes in tertiary albumin structure, revealing some normally inaccessible amino residues. Therefore, removal... 

Figure 21. Acid-catalyzed isomerization of the 3,4-dihydro-2-H-1,3-benzoxazine ring. When all four rings undergo this reorientation it means enantiomerization for the tetrabenzoxazine, and epimerization if the amino residues R1 contain a chiral center.

Preparation of Chemically Modified Collagen Membranes. Collagen membrane was prepared by the above procedure. The lysyl E-amino residues of collagen, in membrane form, were modified to varying degree by reaction with potassium cyanate. The collagen membrane was carbamylated by immersing preswollen films in 0.4M potassium cyanate solution, pH 8.5 for different periods of time. The carbamylation reaction was carried out at ambient temperature (approx. 20°C). The pH of the reaction mixture was monitored with a pH meter and the pH maintained at 8.5 by the addition of 0.05N... 

For a DICE analysis, two different fluorescence dyes, CyDye minimal dyes and CyDye saturation dyes, are available. CyDye minimal dyes react with an NHS-ester bond of lysine e-amino residues and enable coelectrophoresis of up to three different samples in one approach. Eor special applications, e.g., samples from microdissection, the CyDye saturation dyes allow complete 2-D analysis and quantification of protein abundance changes in scarce sample amounts. The dyes react via a maleimide group with all available cysteine residues in the protein sample, giving a high labeling concentration. 

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