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PubMed2006

Adsorption of fluorescently labeled protein residues on poly(ethylene-co-acrylic acid) films modified with affinity functionalities.

Poly(ethylene-co-acrylic acid) (EAA) films were reacted with glycine, 12-aminododecanoic acid, aspartic acid, 5-aminoisophthalic acid, ethanolamine, diethylamine, dimethylamine, N-isopropylamine, and dimethylaminoethyleneamine to prepare EAA films with negatively charged, non-charged, hydrophilic, and hydrophobic functionalities. Attenuated total reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry, and contact angle measurements were used to characterize the modified EAA films. Analyses revealed that the films were modified on the surfaces and also in the bulk; therefore, bulk properties such as cohesive energy density were changed even though the surfaces remained hydrophobic. Adsorption studies were performed for two fluorescently labeled protein residues, dansyl-L-phenylalanine (dansyl-F) and dansyl-L-glutamine (dansyl-Q), from pH 7.4 buffer solutions. The adsorption results revealed that dimethylaminoethyleneamine functionality gave the highest uptake among the functionalities studied, and adsorption was more favorable for dansyl-F than dansyl-Q. Adsorption behavior is discussed in terms of hydrophobic-hydrophobic (dispersion) interactions and Coulombic interactions.

Acrylic Resins↗
PubMed2006

Breakdown kinetics of the tri-chromium(III) oxo acetate cluster ([Cr(3)O(OAc)(6)]+) with some ligands of biological interest.

Kinetics for the breakdown of the trinuclear chromium acetate cluster, [Cr(3)O(OAc)(6)](+), with a series of monoprotic and diprotic ligands in weakly acidic aqueous media (pH approximately 4 or approximately 5) have been investigated spectrophotometrically at 40-60 degrees C. The results point to an ion-pair equilibrium as the first step followed by associative interchange mechanism forming the mononuclear product of the reaction. Pseudo-first-order rates were determined from absorbance data and associated activation parameters were calculated using the Eyring equation. Enthalpy and entropy terms of the reactions (e.g., histidine, DeltaH(double dagger) = 75 +/- 15 kJ mol(-1), DeltaS(double dagger) = -130 +/- 25 J K(-1) mol(-1); lactic acid, DeltaH(double dagger) = 66 +/- 13 kJ mol(-1), DeltaS(double dagger) = -155 +/- 30 J K(-1) mol(-1); glycine, DeltaH(double dagger) = 31 +/- 6 kJ mol(-1), DeltaS(double dagger) = -225 +/- 45 J K(-1) mol(-1)) are consistent with an associative interchange (I(a)) mechanism, and produce a linear isokinetic plot (slope = 50 degrees C). Rates and activation parameters are comparable to those of substitution reactions of the chromium(III) hexaaqua cation. Other ligands studied included malonic acid and the amino acid, aspartic acid. Observed rates are faster than water exchange rates, but typically slower than anion substitution rates, and indicate that trinuclear chromium(III) clusters are expected to be kinetically stable in neutral to slightly acidic conditions.

Chromium↗
PubMed2005

MEKC-LIF of gamma-amino butyric acid in microdialysate: systematic optimization of the separation conditions by factorial analysis.

Micellar electrokinetic chromatography allows the efficient separation of biogenic amines and amino acids in biological samples. Analytes of interest, sample composition, and sample matrix may vary between studies, which necessitates optimization of separations to meet the requirements and conditions of an experiment. Factorial analysis is an efficient tool to accomplish this type of optimization involving multiple interacting factors. The present study describes an optimization procedure for separation of the inhibitory neurotransmitter GABA utilizing capillary electrophoresis with laser induced fluorescence detection. Standards labeled with the flourogenic reagent 3-(2-furoyl)quinoline-2 carboxaldehyde were separated with varying concentrations of borate buffer, beta-cyclodextrin, sodium dodecyl sulfate and pH. The optimized separation method had a correlation coefficient between concentration of GABA and fluorescent signal of 0.98, and was linear in the desired concentration range of 25 nM-10 microM. Glutamic acid, aspartic acid and taurine were also quantified using this separation. When applied to microdialysate collected from the region of the suprachiasmatic nucleus, this separation was able to measure daily variations in GABA levels. The factorial design experiment has proven to be a useful tool, allowing adjustments in the separation of neurotransmitters based on individual requirements.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2002

Thermostability of membrane protein helix-helix interaction elucidated by statistical analysis.

A prerequisite for the survival of (micro)organisms at high temperatures is an adaptation of protein stability to extreme environmental conditions. In contrast to soluble proteins, where many factors have already been identified, the mechanisms by which the thermostability of membrane proteins is enhanced are almost unknown. The hydrophobic membrane environment constrains possible stabilizing factors for transmembrane domains, so that a difference might be expected between soluble and membrane proteins. Here we present sequence analysis of predicted transmembrane helices of the genomes from eight thermophilic and 12 mesophilic organisms. A comparison of the amino acid compositions indicates that more polar residues can be found in the transmembrane helices of thermophilic organisms. Particularly, the amino acids aspartic acid and glutamic acid replace the corresponding amides. Cysteine residues are found to be significantly decreased by about 70% in thermophilic membrane domains suggesting a non-specific function of most cysteine residues in transmembrane domains of mesophilic organisms. By a pair-motif analysis of the two sets of transmembrane helices, we found that the small residues glycine and serine contribute more to transmembrane helix-helix interactions in thermophilic organisms. This may result in a tighter packing of the helices allowing more hydrogen bond formation.

Archaeal Proteins↗
PubMed2000

Simultaneous determination of polycarboxylic acids by capillary electrophoresis with a copper electrode.

The simultaneous determination of polycarboxylic acids including oxalic acid, citric acid, malonic acid, malic acid, tartaric acid, aspartic acid and glutamic acid was achieved by capillary electrophoresis with a copper disk electrode (d = 200 microm). In the system. 0.2 mmol/l cetylpridinium bromide (CPB) was used as an electroosmotic flow (EOF) modifier to reverse the direction of EOF. The effects of the solution pH and CPB concentration on separation were evaluated to achieve the optimum separation conditions. At the working potential of +0.14 V (vs. saturated calomel electrode), the calibration curves for all polycarboxylic acids studied were linear with 2 approximately 3-orders of magnitude and all the detection limits (S/N = 3) were below 15 fmol except malonic acid. Furthermore, the oxalic and citric acids in urine were successfully separated and determined with high sensitivity.

Carboxylic Acids↗
PubMed1999

Lipophorin of female Blattella germanica (L.): characterization and relation to hemolymph titers of juvenile hormone and hydrocarbons.

High density lipophorin (HDLp) from the hemolymph of the German cockroach, Blattella germanica (L.) (Family Blattellidae), has an apparent molecular weight of 670kDa, with an isoelectric point of 7.0 and a density of 1.109g/ml. It is composed of two subunits, apolipoprotein-I (212kDa) and apolipoprotein-II (80kDa), and consists of 51.4% lipid, 46.2% protein and 2.4% carbohydrate. Hydrocarbons constitute 42.2% of the total lipids which also contain diacylglycerol, cholesterol and phospholipid. Lipophorin is rich in the amino acids glutamic acid, aspartic acid, lysine, valine, and leucine. Specificity of a polyclonal antibody was demonstrated by Western blotting and Ouchterlony immunodiffusion: the antiserum recognized native HDLp and apolipoprotein-I, but not apolipoprotein-II, purified vitellin, or other hemolymph proteins. It also recognized a protein in the hemolymph of Supella longipalpa (Blattellidae) but did not cross-react with hemolymph proteins from Periplaneta americana (Blattidae) or Diploptera punctata (Blaberidae). An enzyme-linked immunosorbent assay was developed to measure the HDLp titer in the hemolymph of adult females. The titer of HDLp, a juvenile hormone binding protein, exhibited no clear relationship to the changing titer of juvenile hormone in hemolymph. The hemolymph titer of hydrocarbon, which is also carried by HDLp, showed some functional relation to the concentration of HDLp in the hemolymph. Because it concurrently serves multiple functions in insect development and reproduction, lipophorin titer might covary with the titers of lipid ligands that occur at high concentrations and require extensive shuttling through the hemolymph.

Journal Article↗
PubMed1989

Protein inhibitors of crystal growth.

Nephrocalcin is a urinary glycopeptide that may be a physiological inhibitor of nephrolithiasis. Monomeric nephrocalcin purified from ethylenediaminetetracetic acid-treated urine is 14,000 daltons. Compositional analyses indicate that nephrocalcin is 10 per cent carbohydrate by weight and that 25 per cent of the amino acid residues are acidic (glutamic acid, aspartic acid and gamma-carboxyglutamic acid). Nephrocalcin binds reversibly to calcium oxalate crystals with a dissociation constant of about 0.5 microM. The high collapse pressure of nephrocalcin, 41.5 dynes per cm., measured for a monolayer at the air-water interface, suggests a highly organized structure in which hydrophilic and hydrophobic regions occupy separate regions on the surface of the inhibitor. Nephrocalcin contains the unusual amino acid, gamma-carboxyglutamic acid. Nephrocalcin isolated from urine of stone formers and from kidney stones does not contain gamma-carboxyglutamic acid and it has altered surface properties compared to normal nephrocalcin. The presence of the gamma-carboxyglutamic acid modification and the ability to form stable films with high collapse pressures may be important factors enabling nephrocalcin to prevent stone formation in vivo. The blood of cold water fishes contains antifreeze glycopeptides and/or peptides to prevent it from freezing. The structure of one such antifreeze peptide and its interactions with the crystal lattice of hexagonal ice are discussed as a model for how nephrocalcin might interact with calcium oxalate crystals and arrest their growth in urine.

Amino Acid Sequence↗
PubMedDate not supplied

The short extracellular domain of the T cell receptor zeta chain is involved in assembly and signal transduction.

The zeta chain is required in the TCR complex to guarantee its surface expression and function. However, an understanding of the interaction(s) between the zeta chain and the other proteins in the TCR/CD3 has not yet been achieved. In this report, we attempt to assign a functional role to the short extracellular (EC) domain of the zeta chain by studying its unique positive charge, a lysine at position 9, because of its interesting location to the interchain disulphide bond of the zeta chain homodimer. We show that amino acid exchanges of lysine 9 to glycine, serine, cysteine or asparagine generate TCR complexes which are clearly defective in antigenic signalling. Interestingly, the non-conservative point mutations were segregating TCR complex signalling pathways. However, lysine 9 is not critical for TCR complex surface expression unless the positively charged lysine is exchanged for the negatively charged amino acid aspartic acid. The zeta chain mutant bearing a lysine to cysteine exchange is the sole mutant to be inefficiently co-precipitated with the TCR/CD3 complex suggesting a loose interaction of the zeta chain within the TCR complex.

Amino Acid Sequence↗
PubMed2003

Sugars and amino acids as factors affecting the synthesis of fumonisins in liquid cultures by isolates of the Gibberella fujikuroi complex.

The capacity of four isolates belonging to the Gibberella fujikuroi complex to produce fumonisin B1 and fumonisin B2 when grown in liquid medium supplemented with one sugar and one amino acid at various concentration levels has been investigated. The sugars used for supplementing the medium were glucose, fructose, rhamnose, sucrose, maltose, and trehalose at 5, 10 or 20 g/l. The amino acids used were serine, threonine, glutamic acid, aspartic acid, valine, isoleucine, methionine, glycine, alanine, and cystine at 1 or 10 g/l. Fumonisins were extracted from culture filtrates, purified by SAX column and determined by reversed-phase C18 HPLC with fluorescence detection of the o-phthaldialdehyde derivatives. Two isolates produced very low concentrations of fumonisins with all sugars. The remaining isolates provided increased contents of fumonisins when sugar level increased. Concerning the amino acids, production of fumonisins was also dependent on the isolate, although at 1 g/l, the production of fumonisins was greater than at 10 g/l. The results indicate that the sugar-amino acid-isolate combination is basic in fumonisin biosynthesis and that the particular behaviour of each isolate in the different nutritional conditions may constitute a piece of interesting information in the fields of the Taxonomy, Physiology and Toxicology of these fungi. This is the first report on the influence of the carbon and nitrogen sources on fumonisin production by isolates of the G. fujikuroi complex.

Amino Acids↗
PubMed1988

Isolation and partial characterization of dermatan sulfate proteoglycans from human post-burn scar tissues.

Dermatan sulfate (DS) proteoglycans (PGs) were extracted from human post-burn scar (Sc) tissues with 4M guanidinium chloride and isolated from the extracts by DEAE-cellulose chromatography and by differential ethanol precipitation. The DS.PGs were further purified by Sepharose CL-6B column chromatography. The average molecular weight (Mr) of hypertrophic scar (HSc) tissue DS.PGs was 39,000 based on sedimentation equilibrium measurements. Alkaline borohydride treatment of DS.PGs liberated glycosaminoglycan (GAG) chains and the presence of xylitol indicated that these chains were attached to protein core by xylosyl residues. The average Mr of the DS.GAG chain from HSc and normal scar (NSc) samples were 23,500 and 20,000 respectively. After digestion of the HSc and NSc, DS.PGs with chondroitinase ABC in the presence of proteinase inhibitors, two peptide components with Mr values of 21,500 and 17,000 were detected by SDS-polyacrylamide gel electrophoresis using reducing conditions. Analysis of the protein core fractions derived from NSc and HSc DS.PGs by Sepharose CL-6B column chromatography showed the presence of a single NH2-terminal amino acid (aspartic acid) and also that the fractions with different KAV values had an identical NH2-terminal sequence (A1-A5). The A1-A23 sequence of NSc DS.PG (major fraction, C): NH2Asp-Glu-Ala-O-Gly-Ile-Gly-Pro-Glu-Val-Pro-Asp-Asp-Arg-Asp-Phe-G lu-Pro- Ser-Leu-Gly-Pro-Val was the same as reported for a DS.PG isolated from human fetal membrane (HFM) tissue (Brennan et al., 1984). ELISA inhibition assay using monoclonal antibodies raised in rabbit against the NH2-terminal peptide (containing 15 amino acids) of human fetal membrane tissue were found to cross-react with HSc and NSc DS.PGs. Monoclonal antibodies to bovine skin DS.PGs protein core (Pearson et al., 1983) did not show any cross-reactivity with scar DS.PGs. These results show that the scar DS.PGs described here are different from normal bovine skin DS.PGs in the size and type of the protein core, and that in all the samples, the peptide components have the same NH2-terminal amino acid sequence.

Amino Acids↗
PubMed2002

The human homolog of yeast SEP1 is a novel candidate tumor suppressor gene in osteogenic sarcoma.

The hSEP1 gene is the human homolog of yeast SEP1. Yeast SEP1 is a multifunctional gene that regulates a variety of nuclear and cytoplasmic functions including homologous recombination, meiosis, telomere maintenance, RNA metabolism and microtubule assembly. The function of hSEP1 is not known. We show loss or reduced expression of hSEP1 messenger RNA (mRNA) in three of four primary osteogenic sarcoma (OGS)-derived cell lines and in eight of nine OGS biopsy specimen. In addition, we find a heterozygous missense mutation (Valine(1484)>Alanine) at a conserved amino acid in the primary OGS-derived cell line U2OS. Importantly, we identified a homozygous missense mutation involving a CG-dinucleotide leading to a change in a conserved amino acid, aspartic acid(1137) >asparagine, in the primary OGS-derived cell line, TE85. hSEP1 mRNA expression was nearly undetectable in TE85 and low in U2OS cell lines. None of these mutations were identified in 20 normal samples consisting of bone, cartilage and fibroblast. The hSEP1 gene is located in chromosome 3 at 3q25-26.1 between markers D3S1309 and D3S1569. An adjacent locus defined by the polymorphic markers D3S1212 and D3S1245 has previously been reported to undergo loss of heterozygosity (LOH) at a >70% frequency in OGS and claimed to harbor an important tumor suppressor gene in osteosarcoma. The homozygous mutation in the hSEP1 mRNA in TE85 cell line suggest that this gene itself is subject to LOH. Taken together, these results suggest that hSEP1 acts as a tumor suppressor gene in OGS.

Base Sequence↗
PubMed2004

Rapid prototyping of thermoset polyester microfluidic devices.

This paper presents a simple procedure for the fabrication of thermoset polyester (TPE) microfluidic systems and discusses the properties of the final devices. TPE chips are fabricated in less than 3 h by casting TPE resin directly on a lithographically patterned (SU-8) silicon master. Thorough curing of the devices is obtained through the combined use of ultraviolet light and heat, as both an ultraviolet and a thermal initiator are employed in the resin mixture. Features on the order of micrometers and greater are routinely reproduced using the presented procedure, including complex designs and multilayer features. The surface of TPE was characterized using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Following oxygen plasma treatment, the hydrophilicity of the surface of TPE increases (determined by contact angle measurements) and the proportion of oxygen-containing functional groups also increases (determined by XPS), which indicates a correlated increase in the charge density on the surface. Native TPE microchannels support electroosmotic flow (EOF) toward the cathode, with an average electroosmotic mobility of 1.3 x 10(-4) cm(2) V(-1) s(-1) for a 50-microm square channel (20 mM borate at pH 9); following plasma treatment (5 min at 30 W and 0.3 mbar), EOF is enhanced by a factor of 2. This enhancement of the EOF from plasma treatment is stable for days, with no significant decrease noted during the 5-day period that we monitored. Using plasma-treated TPE microchannels, we demonstrate the separation of a mixture of fluorescein-tagged amino acids (glycine, glutamic acid, aspartic acid). TPE devices are up to 90% transparent (for approximately 2-mm-thick sample) to visible light (400-800 nm). The compatibility of TPE with a wide range of solvents was tested over a 24-h period, and the material performed well with acids, bases, alcohols, cyclohexane, n-heptane, and toluene but not with chlorinated solvents (dichloromethane, chloroform).

Microfluidic Analytical Techniques↗
PubMedDate not supplied

Preparation and characterization of domoic acid-protein conjugates using small amount of toxin in a reversed micellar medium: application in a competitive enzyme-linked immunosorbent assay.

With the aim of producing novel antibodies to domoic acid (DA), an original, rapid, and simple procedure for preparing minute amount of hapten-protein conjugates was developed. The amide-bond-generating mixed anhydride method of Erlanger was performed using 0.32-0.64 micromol of DA in a reversed micellar medium allowing strong carrier haptenization as determined by spectrophotometric measurement. Bovine serum albumin (BSA) and ovalbumin (OVA) conjugates were, respectively, used for immunization of BALB/c mice and antibody screening by enzyme-linked immunosorbent assay (ELISA). Specific polyclonal antibodies were produced upon multiple injections of (DA)(17)-BSA conjugate administered by three different routes: (i) intraperitoneal (i.p.), (ii) intraperitoneal + subcutaneous (i.p. + s.c.), (iii) footpad (f.p.). The i.p. route induced antisera of higher titer (1:350000) than did the other protocols (approximately 1:72900) and was selected throughout further experiments. Using a competitive ELISA format with a peroxidase immunoconjugate and a chromogenic substrate, no significant cross-reactivity was observed with glutamic acid, aspartic acid and kainic acid (KA), a structural analogue of DA. The sensitivity of this assay could be enhanced by 1 order of magnitude by using a beta-galactosidase immunoconjugate with a fluorogenic substrate while preserving DA specificity. The calculated dissociation constant (K(D)) for the interaction of the antibodies with free DA was 5 x 10(-)(7) M (chromogenic assay) and 5 x 10(-)(8) M (fluorogenic assay). Using the optimized assay the limit of detection (LOD) and the limit of quantitation (LOQ) in the ELISA buffer were 1.4 and 3 ng/mL, respectively. Moreover this assay was found applicable for measuring DA levels in spiked mussel extracts pre-cleaned through a solid-phase extraction column, as a very good correlation (r(2) = 0.96) was observed between the actual amounts of DA added and amounts detected by ELISA. Thus, accurate determinations of DA in clean extracts could be achieved between 2 and 180 ng/mL in spiked samples which corresponds to 0.02-1.8 microg/g of original mussel tissue. Owing to the regulation limits of 20 microg DA/g of shellfish tissue, these extraction and assay procedures should provide a useful complement to the standard HPLC analytical technique currently employed in monitoring DA in shellfish tissue.

Animals↗
PubMed1986

Interaction of enkephalins and des-tyrosyl-enkephalins with synaptosomal plasma membrane vesicles: enkephalin binding and inhibition of proline transport.

Leucine- and methionine-enkephalins inhibit the Na+-dependent transport of proline into plasma membrane vesicles derived from synaptosomes. Glycine transport is weakly inhibited by enkephalins whereas there is no inhibition of transport of glutamic acid, aspartic acid, or gamma-aminobutyric acid. The inhibition of proline uptake is observed with des-tyrosyl-enkephalins but not with morphine, dynorphin(1-13), or beta-endorphins. Furthermore, enkephalin-induced inhibition of proline transport is not antagonized by naloxone. [Leu]enkephalinamide and modified [Leu]enkephalins with greater selectivity for the delta-subclass of enkephalin binding sites are less effective than [Leu]enkephalin in the inhibition of proline transport. Specific binding of [3H]Leu-enkephalin to the plasma membrane vesicles is demonstrated, and des-Tyr-[Leu]enkephalin competes with Leu-enkephalin for [Leu]enkephalin binding sites. The similarity in the concentrations of des-Tyr-[Leu]enkephalin required to compete for specific [Leu]enkephalin binding and to inhibit proline transport suggests that a specific subclass of enkephalin binding sites, distinguished by their recognition of both the enkephalins and their des-tyrosyl derivatives, may be associated with the synaptic proline transport system.

Amino Acids↗
PubMed1989

Carboxypeptidase-mediated release of methotrexate from methotrexate alpha-peptides.

Methotrexate (MTX) alpha-peptides containing representative neutral (alanine), acidic (aspartic acid), and basic (arginine) amino acids were synthesized by a regiospecific route. Purity and authenticity of MTX-Ala, MTX-Asp, and MTX-Arg were established by TLC, HPLC, elemental analysis, and NMR and absorbance spectra. These peptides were hydrolyzed by carboxypeptidases to yield MTX and the amino acids. Reactions were monitored by using a ninhydrin assay for the amino acids and HPLC and spectrophotometric assays for MTX. Pancreatic carboxypeptidase A (CP-A) hydrolyzed MTX-Ala and, at a much slower rate, MTX-Asp and MTX-Arg. MTX-Ala was also a substrate for pancreatic carboxypeptidase B (CP-B); marginal activity was observed with this enzyme and MTX-Arg. Human serum hydrolyzed only MTX-Arg; biphasic inhibition of this activity by 2-(mercaptomethyl)-3-(guanidinoethyl)thiopropionate was consistent with the known presence of two types of endogenous carboxypeptidase (CP-N). Cytotoxicity of the MTX peptides toward L1210 cells in culture was enhanced considerably in the presence of the appropriate carboxypeptidases. MTX-Ala was much less toxic than MTX (ID50 values of 2.0 X 10(-6) M and 2.4 x 10(-8) M, respectively), but in the presence of CP-A the ID50 of the peptide improved to 8.5 X 10(-8) M. Similar results were obtained with MTX-Asp/CP-A and MTX-Ala/CP-B combinations. MTX-Arg showed good cytotoxicity (ID50 of 5.0 X 10(-8) M), due to CP-N activity in the fetal bovine serum of the culture medium; inclusion of CP-B lowered the ID50 to that of MTX. Possible clinical uses of MTX peptides are discussed.

Amino Acids↗
PubMed2006

Tumor targeting by surface-modified protein microspheres.

Protein microspheres have been used in the fields of biomedical imaging and drug delivery, but surface modification for cell targeting has been problematic. We have for the first time used an electrostatic adhesion approach to adhere arginine-glutamic acid-aspartic acid (RGD) containing peptides to the surface of protein microspheres for the purpose of targeting these vesicles to tumor cells. RGD sequences are recognized by integrin membrane receptors, which are overexpressed in various tumors. We have succeeded in modifying the surface of serum albumin core-shell microspheres, which have a fluorescent nonaqueous core by using several polylysine peptides containing the RGD sequence. Fluorescence microscopy reveals that these modified microspheres are selectively bound and taken up by HT29 human colon cancer cells in vitro.

Antineoplastic Agents↗
PubMed2006

Changes in the free amino acid contents of honeys during storage at ambient temperature.

This study was carried out to establish the changes in the free amino acid contents of floral honeys, honeydew honeys, and blend honeys during storage at room temperature and to test the capacity of the amino acids to distinguish the origin of the honeys after storage. For this purpose, 54 artisanal honeys (39 floral, 5 honeydew, and 10 blend) were studied. Samples were taken from recently collected honeys and at 3, 6, 9, 12, 16, 20, and 24 months after harvesting. The contents of most of the free amino acids were found to decrease with storage time, with the greatest reduction observed in the first 9 months. The contents of the amino acids aspartic acid, beta-alanine, and proline increased in the first few months after storage, reaching maximum values at 6 months, suggesting the possible existence of enzymatic activities. The application of stepwise discriminant analysis to the free amino acid content data demonstrated that the contents of the amino acids valine, beta-alanine, gamma-aminobutyric acid, serine, isoleucine, alpha-alanine, ornithine, and glutamine correctly assigned 87% of honeys to their group of origin: floral, honeydew, or blend.

Amino Acids↗
PubMed2001

Synthesis of boronic acid analogues of alpha-amino acids by introducing side chains as electrophiles.

A synthetic route has been developed which has allowed us to prepare novel alpha-aminoboronic acids as inhibitors of serine proteases. These compounds were prepared to study the roles of proteases in biological systems. This methodology affords alpha-aminoboronic acids with the general formula R'-NHCH(R)BO(2)-pinanediol, where R = -CH(2)CHF(2), -CH(2)CO(2)tBu, and -(CH(2))(2)CO(2)Me and R' = either H or C(O)R". The latter two compounds are the boronic acid analogues of the natural amino acids aspartic acid and glutamic acid with the side chain carboxylate protected as a tert-butyl or a methyl ester, respectively. Following acylation of the amino group, the side chain tert-butyl ester of boroaspartic acid was removed by treatment with TFA. Boroglutamic acid was obtained as the free boronic acid by hydrolysis with HCl. Prior syntheses of alpha-aminoboronic acids involve the initial addition of an organometallic reagent to a trialkyl borate ester. These conditions do not allow the preparation of compounds with functionalities that are not stable to the strongly basic reaction conditions. The methodology described here allows the preparation of alpha-aminoboronic acids by introducing side chains as electrophiles. This is particularly advantageous for side chains which are prone to elimination or unwanted enolate formation. Specifically, BrCH(2)CHF(2), BrCH(2)COO(t)Bu, and CH(2)=CHCOOMe were allowed to react with the stabilized anion of (phenylthio)methane boronate, PhSCH(2)BO(2)C(6)H(12), to give the substituted boronate. The substituted (phenylthio)methane boronate was converted to the corresponding sulfonium ion by treatment with methyl iodide and subsequently displaced with iodide. The alpha-iodo derivative was converted to the amine by conventional methods.

Amino Acids↗