N-substituted Amino Acids Research Articles

Synthesis of polymeric N-hydroxysuccinimide esters of N-substituted amino acids and peptides

1 A number of macrosieve poly-N-hydroxysuccinimide esters of N-protected amino acids and peptides was synthesized using the following methods for the condensation of the polymer-activator with the carboxyl components: dicyclohexylcarbodiimide, mixed anhydrides, trifluoroacetate, and a method that is based on the use of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline as the condensing agent. 2. A comparative evaluation was made of the efficiency of the indicated methods for the condensation of N-protected amino acids and peptides with the polymer-activator as regards the yield of polymeric esters, the consumption of the carboxyl component, and the length of the activation process. 3. It was shown that the trifluoroacetate and mixed anhydride methods are the most efficient.

Effect of variations in peptide parameters and charges on the unperturbed dimensions of polypeptide chains

The net charges on various atoms of poly (l-alanine), polyglycine, poly (N-methyl-l-alanine) and poly (N-methylglycine) were computed using the MOLCAO method of Del Re forσ charges and the Huckel MO method forπ charges. The characteristic ratiosC∞ were computed for all the above polypeptide chains, with different sets of parameters for the peptide unit. The calculated values ofC∞ are found to be very sensitive to the input peptide geometry. The calculated value of 2·2 forC∞ of poly (N-methylglycine) obtained with set-3 parameters (derived from a crystal structure containing prolyl residue) is closer to the experimental value of 1·8±0·2 than the value of 2·7 obtained with set 1 (Pauling-Corey parameters), suggesting that the peptide parameters of N-substituted aminoacids have close similarity to set 3 rather than to set 1. The calculated values ofC∞ of the polypeptide chains show no correlation with the number of allowed conformations, suggesting that the ratio ofC∞/Cf need not always provide information about the flexibility or freedom of rotation of chain units.

Renal transport of amino acids.

According to recent experimental data the renal transport of amino acids (AA) is characterized as follows. 1.Kinetics: Several reabsorption systems remove AA from the tubular fluid by active transport with Michaelis-Menten type kinetics. Passive diffusion does play only a relatively small role in reabsorption, but determines the pump leak steady state concentration at the end of the tubule. 2.Stereospecificity: Except for aspartate the naturally occurring L-analogs show a much larger affinity to the transport “carriers” than the D-isomers do. 3.Specificity: Separate transport mechanisms exist for a) the “acidic” AA (Glu and Asp); b) the “dibasic” AA (Arg, Lys, Orn); c) cystine/cysteine; d) the “imino” acids (Pro, OH-Pro and other N-substituted AA); e) the β- and γ-AA (β-Ala, GABA, Taurine); f) all other “neutral” AA. For the group (d) and maybe also for (b) and glycine additional low capacity/high affinity systems exist. 4.Localization: Except for glycine and taurine under normal conditions more than 80% of the filtered load are reabsorbed within the first third of the proximal tubule. At an elevated load the rest of the proximal tubule (including pars recta) but not the distal nephron is included into the reabsorptive process. AA are also taken up from the peritubular blood. 5.Energy sources: At least the main part of AA uptake at the brushborder membrane is dependent from a transmembranal Na+-gradient which in turn is established by the ATP driven Na+-pumps at the basolateral side of the cell (Secondary active transport or co-transport of AA). 6.Biochemistry: The biochemical nature of the AA-“carriers” is unknown. The recent hypothesis that a “γ-glutamyl cycle” plays a major role in this context has been disproved to great extent. 7.Peptides: Oligopeptides (Angiotensin, Glutathion) filtered at the glomerulum are hydrolyzed by brushborder peptidases within the tubule lumen. The splitting products, the free constituent amino acids, are reabsorbed subsequently by their respective transport systems.

Crystal and molecular structure of copper complexes with N-substituted alpha amino acids

Crystal and molecular structure of copper complexes with N-substituted alpha amino acids

Crystal and molecular structure of complexes of copper with N-substituted alpha amino acids

Crystal and molecular structure of complexes of copper with N-substituted alpha amino acids

Solutions of N-substituted amino acids. IV. Tautomerism in N,N-Di-n-butyl- -, - -, and - -amino acids.

Solutions of N-substituted amino acids. IV. Tautomerism in N,N-Di-n-butyl- -, - -, and - -amino acids.

Hydrolysis of ester substrates of trypsin and chymotrypsin by barley carboxypeptidase

Purified barley carboxypeptidase exhibits high activity against a number of N-substituted amino acid esters, which are commonly used as synthetic substrates for mammalian and microbial proteinases. The proteinases of barley, on the contrary, do not hydrolyse these compounds. Because many other plants contain carboxypeptidases closely resembling the barley enzyme, we conclude that synthetic ester substrates should not be used to detect proteinase activity in extracts of higher plants. Plant carboxypeptidases also liberate C-terminal tryptophan from α-casein. Therefore, casein also is an unreliable substrate for plant proteinases.

Alkaline protease from Aspergillus oryzae: Esterase activity

Kinetic data are presented for the hydrolysis of N-substituted amino acid esters by aspergillopeptidase B, an alkaline protease from Aspergillus oryzae. The rate of hydrolysis was followed with a pH-stat at pH 8.5, 25°C and ionic strength 0.1. The overall susceptibility of N-acetyl amino acid esters to hydrolysis decreases in the order of Phe, Tyr > Trp > Met > Leu > Lys > His ⪢ Val, Gly. The N-benzoyl derivatives of His, Lys and Arg methyl esters are approximately thirty times more reactive than the corresponding acetyl derivates. Amino acid esters with free α-amino groups are unable to serve as substrates. These data clearly suggest that before an amino acid ester can serve as a substrate for the alkaline protease of A. oryzae (a) the α-amino group must be blocked and (b) an aromatic group is required either in the amino acid side chain or as the N-terminal blocking group. It further suggests that the binding of substrate to the enzyme active site probably takes place through hydrophobic binding. The hydrolysis of N- benzoyl- l-arginine ethyl ester by aspergillopeptidase B showed a sigmoid pH-velocity profile which could be fitted with a calculated titration curve for a single group with a p K′ of 6.42 at 20°C and 6.02 at 35°C, giving a ΔH i of 9.1 kcal per mole at 0°C. These data suggest that the enzyme may require a non-protonated imidazole group for activity.

Dextran derivatives III. Synthesis of esters of dextran with n-substituted amino acids by the mixed anhydride method and study of the conditions for eliminating the protective groups

1. New methods for the O-aminoacylation of dextran (“polyglucin”) with mixed anhydrides of N-protected amino acids with benzenesulfonyl chloride, tosyl chloride, ethyl chloroformate, and phosphorus oxychloride have been proposed.

Electron spin resonance of radicals in X-irradiated single crystals of N-substituted amino acids

(1971). Electron spin resonance of radicals in X-irradiated single crystals of N-substituted amino acids. Molecular Physics: Vol. 21, No. 3, pp. 551-554.

Electron spin resonance of radicals in X-irradiated single crystals of N-substituted amino acids

Electron spin resonance of radicals in X-irradiated single crystals of N-substituted amino acids

N-Substituted amino acids in serum of patients with chronic renal insufficiency

Three N-substituted amino acids were determined in sera from healthy subjects: glycine, glutamic acid and α-alanine (traces only of the last). In the serum of uremic patients the levels of these amino acids were significantly increased; moreover, aspartic acid, cystine, phenylalanine and proline (all in trace quantities) were detected. Next, amino acids found in the N-substituted form were determined quantitatively in blood peptides. The levels of all examined peptide-bound amino acids, except aspartic acid, were significantly changed in uremia: α-alanine, cystine, phenylalanine and glutamic acid levels were significantly decreased, while the ratio of the N-substituted to peptide-bound amino acids was elevated, and the levels of peptide bound glycine were significantly increased.

Enzymatic Hydrolysis of N-Substituted Aminoacyl Transfer Ribonucleic Acid in Yeast

Abstract An N-substituted aminoacyl transfer RNA hydrolase (ribonuclease free) has been isolated, purified 230-fold, and crystallized from yeast supernatant. The purified enzyme is activated by 10-3 and 10-2 m MgCl2 and strongly inhibited by 10-1 m MgCl2. The hydrolase is also strongly inhibited by 10-2 m ethylenediaminetetraacetic acid, and the inhibition can be completely overcome with 10-2 m MgCl2. The yeast hydrolase is competitively inhibited by uncharged yeast tRNA. Purified yeast ribosomal RNA does not inhibit the enzyme. The hydrolase does not show a strict species specificity since the tRNA of both yeast and Escherichia coli can be used to form substrate. N-Acetyl-valyl-adenosine is not a substrate for the hydrolase and N-acetyl-valyl-oligonucleotide is hydrolyzed very slowly. Although the free aminoacyl-tRNAs tested are resistant or very slowly hydrolyzed, the derivatives N-acetylaminoacyl-tRNA, N-benzoyl-glycyl-glycyl-phenylalanyl-tRNA, and N-benzoyl-glycyl-glycyl-glycyl-phenylalanyl-tRNA are all readily hydrolyzed by the purified enzyme. Yeast oligolysyl-tRNA is very slowly hydrolyzed by the enzyme. N-Substituted amino acids and tRNAs are the products of hydrolysis of N-substituted aminoacyl-tRNAs. Enzymatically deacylated tRNAs can be recharged with their corresponding amino acids.

Amino acid conjugates in blood and urine. I. A simple method for N-substituted amino acid determination.

Eine neue, vereinfachte, elektrophoretische Trennungstechnik zur quantitativen Bestimmung von Aminosauren in Korperflussigkeiten in konjugierter Form oder als ninhydrin-negative Polypeptide wird beschrieben.

Solutions of N-substituted amino acids. 3.

Solutions of N-substituted amino acids. 3.

A new method of synthesizing 3?(2?)-O-aminoacylnucleosides and nucleotides

1. A new method of synthesizing 3′- and 2′-O-aminoacylnucleosides and aminoeylnucleotides based on the activation of N-substituted amino acids with imidazole was developed. 2. In using this method, it is most convenient to use the o-nitrophenylsulfenyl protection for the amino acid when preparing O-aminoacylnueleosides, and the tert-butyloxycarbonyl group in the case of 5′-nucleotides.

Solutions of N-substituted amino acids. II. N-ethyl-N-phenyl-beta-aminopropionic acid as a probe of hydrogen-bonding basicities.

Solutions of N-substituted amino acids. II. N-ethyl-N-phenyl-beta-aminopropionic acid as a probe of hydrogen-bonding basicities.

α-arylmethylamino acids

N-substituted amino acids with benzyl, veratryl or skatyl residues on the amino group have been synthesized, and their Chromatographie and electrophoretic behavior has been studied. A method of acetylating N-substituted amino acids has been worked out.

Nuclear Magnetic Resonance Spectra of Amines III. Identification of N-Substituted Amino Acids

Spectra of N-substituted amino acids examined in alkaline deuterium oxide and in trifluoroacetic acid show chemical shifts and first-order spin-spin splitting patterns that are useful for identification of N-methyl, N-methylene, N-phenyl, and other groups attached to the nitrogen of an amino acid. Spectra of N-substituted amino acids examined in alkaline deuterium oxide and in trifluoroacetic acid show chemical shifts and first-order spin-spin splitting patterns that are useful for identification of N-methyl, N-methylene, N-phenyl, and other groups attached to the nitrogen of an amino acid.

ESTERASE ACTIVITY OF PEPSIN.

IT is known that many proteolytic enzymes—trypsin, chymotrypsin, thrombin, papain and others—hydrolyse peptide, amide and ester bonds. Pepsin, however, is generally believed to hydrolyse the peptide bonds only, without exhibiting the esterase activity1. This conclusion is based on observations which suggest that pepsin does not hydrolyse the ester bonds in several esters of N-substituted amino-acids and peptides, but no special investigation of the esterase activity of pepsin has been published.