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At least 1,045 records · Page 58Linked to original sources
PubMed1984

Thermodynamic bases for fatty acid ethyl ester synthase catalyzed esterification of free fatty acid with ethanol and accumulation of fatty acid ethyl esters.

Myocardial homogenates rapidly synthesize fatty acyl ethyl esters from nonesterified fatty acid and ethanol in the absence of coenzyme A or ATP, and the enzyme catalyzing this reaction, fatty acid ethyl ester synthase, has been purified 5400-fold to homogeneity [Mogelson, S., & Lange, L. G. (1984) Biochemistry (preceding paper in this issue)]. To define the factors permitting this de novo synthesis of ester bonds and the consequent accumulation of fatty acyl ethyl esters in myocardium, we determined thermodynamic parameters relevant to the kinetics and equilibria of this reaction and specifically characterized (1) the rates of synthesis of ethyl oleate, in both the presence and absence of purified enzyme catalyst, and (2) the physical properties of the product, ethyl oleate, in an aqueous milieu. Compared to the reaction of ethanol and oleate in the absence of catalyst, fatty acid ethyl ester synthase enhanced the rate of ethyl oleate synthesis by reducing the free energy of activation (delta G) from 32.5 to 19.9 kcal/mol, effected in large part by a positive entropy shift, delta Senz - delta S uncat = 23.9 cal/(mol.deg). Rate constants in the presence and absence of enzyme at 37 degrees C were 6 X 10(-2) s-1 and 7.8 X 10(-11) M-1 s-1, respectively, indicating a catalytic power of at least 10(8)M for this enzyme. Kinetic data indicated an enzymatic Vmax of 1.25 nmol/(mg.s) (37 degrees C). The equilibrium constant was calculated for the reaction oleate + ethanol in equilibrium ethyl oleate and was 0.095 M-1 at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Acyltransferases↗
PubMed2001

An NMR and ab initio quantum chemical study of acid-base equilibria for conformationally constrained acidic alpha-amino acids in aqueous solution.

The protonation states of a series of piperidinedicarboxylic acids (PDAs), which are conformationally constrained acidic alpha-amino acids, have been studied by (13)C NMR titration in water. The resulting data have been correlated with theoretical results obtained by HF/6-31+G calculations using the polarizable continuum model (PCM) for the description of water. The PDAs are highly ionizable and contain one or two possible internal hydrogen bonds. In the present study, we show that the PCM model is able to reproduce the relative stabilities of the different protonation states of the PDAs. Furthermore, our results show that prediction of relative pK(a) values for two different types of ionizable functional groups covering a pK(a) range from 1.6 to 12.1 is possible with a high degree of accuracy.

Acid-Base Equilibrium↗
PubMed2004

pH-Dependent chemoselective synthesis of alpha-amino acids. Reductive amination of alpha-keto acids with ammonia catalyzed by acid-stable iridium hydride complexes in water.

An acid-stable hydride complex [Cp*IrIII(bpy)H]+ {1, Cp* = eta5-C5Me5, bpy = 2,2'-bipyridine} serves as the active catalyst for the highly chemoselective synthesis of alpha-amino acids by reductive amination of alpha-keto acids with aqueous NH3 and HCOO- in water at pH 5-8. pH-dependent catalytic 15N- and 2H-double-labeling has also been accomplished by using 15NH3 and DCOONa, which are ideal amine and hydride ion sources, respectively.

Amination↗
PubMed2003

Peptide backbone folding induced by the C(alpha)-tetrasubstituted cyclic alpha-amino acids 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) and 1-aminocyclopentane-1-carboxylic acid (Ac5c). A joint computational and experimental study.

The conformational study of a new group of synthetic peptides containing 4-amino-1,2-dithiolane-4-carboxylic acid (Adt), a cysteine-related achiral residue, has been carried out through a joint application of computational and experimental methodologies. Molecular Dynamics simulations clearly suggest the tendency of this molecule to adopt a gamma-turn conformation in vacuum and help in analyzing the complex and crucial conformational behaviour of the dithiolane ring which appears to preferentially adopt a C(S)-like structure. Electronic structure calculations carried out in solution using the Density Functional Theory also indicate the preservation of the gamma-like folding in apolar solvents and the helix-like one in more polar solvents. A comparison with the achiral 1-aminocycloalkane-1-carboxylic acid (Ac5c) has been carried out using the same computational tools. NMR and IR data on dipeptide derivatives containing the Adt or Ac5c residue show that in chloroform solution all the models prefer a gamma-turn structure, centered at the cyclic residue, stabilized by an intramolecular H-bond, whereas in a more polar solvent, i.e. dimethyl sulfoxide, this folding is not maintained. The experimental conformational studies, extended to N-Boc protected tripeptides, clearly indicate the remarkable tendency of both the five-membered C(alpha)-tetrasubstituted cyclic amino acids Adt and Ac5c to induce the gamma-turn structure also in models able to adopt the beta-bend conformation.

Amino Acids↗
PubMed1974

The enzymic and non-enzymic degradation of colneleic acid, an unsaturated fatty acid ether intermediate in the lipoxygenase pathway of linoleic acid oxidation in potato (Solanum tuberosum) tubers.

Colneleic acid is an unsaturated ether fatty acid derived from linoleic acid via a lipoxygenase-mediated enzyme pathway. It is degraded (a) by an enzyme in potato tubers which is heat-labile and non-dialysable and (b) by a model system containing catalytic amounts of Fe(2+) ions. Both enzyme- and Fe(2+)-catalysed systems have similar properties with respect to pH optima (pH5.0-5.5), oxygen requirement (0.6-0.7 mol of O(2) consumed/mol of ether degraded), inhibitors and reaction products. An unstable product breaks down to C(8) and C(9) carbonyl fragments. Both systems are inhibited by low concentrations of antioxidants (e.g. 5mum-butylated hydroxytoluene) and some chelating agents (e.g. 5mum-diethyldithio-carbamate). The model system is strongly inhibited by metal ions, particularly Cu(2+) and Fe(3+), at 20mum. Hydrogen peroxide and haemoproteins do not substitute for the enzyme or Fe(2+) ions but the non-haem iron protein, ferredoxin, does catalyse the degradation.

Antimetabolites↗
PubMed1997

Electrospray analysis of biological samples for trace amounts of trichloroacetic acid, dichloroacetic acid, and monochloroacetic acid.

Trichloroethylene (TCE) has been identified as a widespread groundwater contaminant. Trichloroacetic acid (TCA) and dichloroacetic acid (DCA) are toxicologically relevant metabolites of TCE that produce tumors in B6C3F1 mice. A sensitive method for measuring these metabolites in plasma has been developed to obtain pharmacokinetic data from TCE exposure. This is particularly important because DCA is more potent at producing hepatoproliferative lesions than TCA. At present, it is unclear whether DCA is produced by humans. Existing gas chromatographic methods cannot detect DCA at low nanogram-per-milliliter levels. A Finnigan TSQ 700 mass spectrometer (MS) with electrospray ionization was used to measure TCA, DCA, and monochloroacetic acid (MCA) in plasma. The MS was operated in negative ion tandem MS mode. The limit of detection for TCA and DCA was 4 ng/ml, and the limit of detection for MCA was 25 ng/mL. Plasma samples from human subjects exposed to 100 ppm TCE for 4 h contained TCA at concentrations as high as 10 micrograms/mL. DCA concentrations were less than 5 ng/mL, and MCA was not detected (less than 25 ng/mL).

Acetates↗
PubMed1986

Structural studies on N-acetylmannosaminuronic acid-containing and glucuronic acid-containing teichuronic acids in the cell wall of Bacillus megaterium AHU 1375.

Structural studies were carried out on two kinds of teichuronic acid-glycopeptide complexes (designated as TU-GP-I and TU-GP-II) isolated from lysozyme digest of N-acetylated cell walls of Bacillus megaterium AHU 1375 by ion-exchange chromatography and gel chromatography. TU-GP-I, accounting for about 25% of the cell walls, contained N-acetylmannosaminuronic acid, N-acetylglucosamine, glucose, galactose, glycerol, and phosphorus in an approximate molar ratio of 1:1:2:1:0.5:0.5, together with small amounts of glycopeptide components. TU-GP-II, accounting for about 9% of the cell walls, contained glucuronic acid, glucose, and fucose in a molar ratio of about 2:1.5:1, together with small amounts of glycopeptide components. The results of analyses involving Smith degradation, chromium oxidation, methylation, acetolysis, and H-NMR measurement led to the conclusion that the polysaccharide chain of TU-GP-I comprised repeating units,----6) Glc(alpha 1----3)-ManNAcUA(beta 1----4)[Gal(alpha 1----3)][Glc(beta 1----6)]GlcNAc(beta 1----. About half of the repeating units were substituted by glycerophosphoryl residues at C-6 of the beta-glucosyl residues linked to the N-acetylglucosamine residues. By means of a similar procedure, the polysaccharide chain of TU-GP-II was shown to comprise repeating units,----4)GlcUA(alpha 1----3)GlcUA(alpha 1----3)Glc(alpha 1----3)Fuc(alpha 1----, of which about half were substituted by alpha-glucosyl residues at C-3 of the 4-substituted glucuronosyl residues.

Bacillus megaterium↗
PubMed1992

Cellular localization of mRNA for cellular retinoic acid-binding protein II and nuclear retinoic acid receptor-gamma 1 in retinoic acid-treated human skin.

We have previously shown that cellular retinoic acid-binding protein II (CRABP-II), but not cellular retinoic acid-binding protein I (CRABP-I), mRNA expression is markedly induced in human skin by topical retinoic acid. In the present study, we have investigated the pattern of expression of CRABP-II transcripts in 4-d RA-treated human skin by non-radioactive in situ hybridization (n = 5) and Northern analysis (n = 4). RA induced accumulation of CRABP-II transcripts throughout the epidermis, dermal fibroblasts, and endothelial cells as determined by in situ hybridization. In skin treated with vehicle, a faint hybridization signal was observed only in basal layers of the epidermis consistent with low-level expression of CRABP-II mRNA. RA-mediated accumulation of CRABP-II transcripts in skin was also confirmed by Northern analysis. Neither RA nor vehicle induced significant changes in nuclear RA receptor-gamma 1 or keratin 5 gene expression in skin as determined by in situ or Northern hybridization. These results indicate that RA-induced CRABP-II mRNA accumulation is primarily localized to spinous and granular layers in epidermis, and in superficial dermis.

Administration, Topical↗
PubMed1994

The amino acid sequence of the red kidney bean Fe(III)-Zn(II) purple acid phosphatase. Determination of the amino acid sequence by a combination of matrix-assisted laser desorption/ionization mass spectrometry and automated Edman sequencing.

Purple acid phosphatase of the common bean Phaseolus vulgaris is a homodimeric 110-kDa glycoprotein with a Fe(III)-Zn(II) center in the active site of each monomer. After exchange of Zn(II) for Fe(II), the enzyme spectroscopically and kinetically resembles the mammalian purple acid phosphatases with Fe(III)-Fe(II) centers in monomeric 35-kDa proteins. The kidney bean enzyme consists of 432 amino acids/monomer with five N-glycosylated asparagine residues. The complete amino acid sequence was determined by a combination of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and classical sequencing methods. Our strategy involved mass determination and sequence analysis of all cyanogen-bromide-generated fragments by automated Edman degradation. Limited cleavages with cyanogen bromide were performed to obtain fragments containing still uncleaved Met-Xaa linkages. MALDI mass spectra of these products allowed the characterization of each fragment and the determination of the order of the cyanogen bromide fragments in the intact protein without producing overlapping peptides. For one large 30-kDa methionine-free fragment, the alignment of the Edman-degraded tryptic peptides was obtained by MALDI-MS analysis and enzymic microscale peptide laddering of overlapping Glu-C-generated fragments. The employed strategy shows that the classical method, in combination with modern mass spectrometry, is an attractive approach for primary structure determination in addition to the DNA sequencing method.

Acid Phosphatase↗
PubMed2003

Amino acid conjugates: metabolites of 2-propylpentanoic acid (valproic acid) in epileptic patients.

In this study, spectroscopic and chromatographic evidence is presented for the identification and characterization of the metabolites, valproyl glutamate (2-propylpentanoyl glutamate, VPA-GLU) and valproyl glutamine (2-propylpentanoyl glutamine, VPA-GLN) in the urine, serum, and cerebrospinal fluid (CSF) of patients on valproic acid (VPA) therapy. Moreover, the identification of valproyl glycine (2-propylpentanoyl glycine, VPA-GLY) in the serum and urine of patients on VPA, albeit in trace concentrations, is also reported here. The three amino acid conjugates excreted in urine accounted for about 1% of the VPA dose in four patients who were on VPA therapy chronically and had reached steady state. VPA-GLU was quantitatively the most prominent metabolite (0.66-13.1 microg/mg creatinine) compared with VPA-GLN (0.78-9.93 microg/mg creatinine) and VPA-GLY (trace-1.0 microg/mg creatinine) in overnight urine samples of all patients studied (n = 29). The relatively low serum concentrations of the three amino acid conjugates of VPA in six patients suggest that the metabolites are readily excreted once formed. In contrast, whereas VPA GLY was absent in the CSF of one patient on VPA, the concentrations of VPA-GLU and VPA-GLN in this CSF sample were 9 and 5 times, respectively, their corresponding serum concentrations.

Adolescent↗
PubMed2003

Contribution of fatty acids released from lipolysis of plasma triglycerides to total plasma fatty acid flux and tissue-specific fatty acid uptake.

There is controversy over the extent to which fatty acids (FAs) derived from plasma free FAs (FFAs) or from hydrolysis of plasma triglycerides (TGFAs) form communal or separate pools and what the contribution of each FA source is to cellular FA metabolism. Chylomicrons and lipid emulsions were labeled with [(3)H]triolein, injected into mice, and appearance in plasma of [(3)H]oleic acid was estimated, either through a steady-state approach or by compartmental modeling. [(14)C]oleic acid was included to trace plasma FFA. Eighty to 90% of triglyceride (TG) label was recovered in plasma, irrespective of tracer method or TG source. The contribution of TG lipolysis to total plasma FA turnover was 10-20%. After infusion of [(3)H]TG and [(14)C]FA, the retention of these labels varied substantially among liver, adipose tissue, and skeletal and heart muscle. Retention of TG label changed during fasting in the same direction as lipoprotein lipase (LPL) activity is regulated. We propose a model that reconciles the paradoxical 80-90% loss of TG label into plasma with LPL-directed differential uptake of TGFA in tissues. In this model, TGFAs mix locally at the capillaries with plasma FFAs, where they would lead to an increase in the local FA concentration, and hence, FA uptake. Our data indicate that a distinction between TG-derived FA and plasma FFA cannot be made.

Adipose Tissue↗
PubMed1980

Enterohepatic recycling of phenolphthalein, morphine, lysergic acid diethylamide (LSD) and diphenylacetic acid in the rat. Hydrolysis of glucuronic acid conjugates in the gut lumen.

1. Biliary elimination in female Wistar albino rats 3 h after i.p. injection of [3H]phenolphthalein, [3H]morphine, 14C-LSD and [14C]diphenylacetic acid was 90%, 45%, 75% and 57% respectively, predominantly as glucuronides. 2. Infusion of 3 h bile from the previous experiments into the duodena of bile-duct-cannulated animals demonstrated enterohepatic circulation, amounting in 24 h to 85%, 41%, 28% and 66% of the infused doses of the conjugates of phenolphthalein, morphine, LSD and diphenylacetic acid respectively. 3. Pretreatment with antibiotics to suppress intestinal microflora decreased this enterohepatic recirculation to 22%, 8.6% and 21% in 24 h for phenolphthalein, morphine and diphenylacetic acid glucuronides respectively. Antibiotic pretreatment did not influence the absorption and re-excretion of infused doses of the free aglycones, thus demonstrating the importance of bacterial beta-glucuronidase hydrolysis of the biliary conjugates. 4. The extent of intestinal absorption of the aglycones after bacterial beta-glucuronidase hydrolysis of the conjugates is related to their lipid-solubility as estimated by octan-1-ol:0.1 M phosphate buffer partition ratios (P-values). 5. The persistence of compounds in the enterohepatic circulation is determined by the faecal and urinary elimination of the circulating compounds. Faecal elimination is governed by the extent of intestinal absorption of the circulating compounds, which is influenced by the efficacy of intestinal hydrolysis of the conjugates and the relative lipophilicity of the aglycones released.

Animals↗
PubMedDate not supplied

Pharmacokinetics and pharmacodynamics of valproate analogs in rats. III. Pharmacokinetics of valproic acid, cyclohexanecarboxylic acid, and 1-methyl-1-cyclohexanecarboxylic acid in the bile-exteriorized rat.

The pharmacokinetics of valproic acid (VPA) and its structural analogs cyclohexanecarboxylic acid (CCA) and 1-methyl-1-cyclohexanecarboxylic acid (MCCA) were examined in bile-exteriorized rats. A 0.52 mmol/kg dose (equivalent to 75 mg/kg VPA) of test compound (N = 4 rats per compound) was administered as an intravenous bolus. VPA, CCA, and MCCA concentrations in serum, bile, and urine were determined by gas chromatography before and after incubation in sodium hydroxide to hydrolyze base-labile conjugates. Concentration-time profiles of these compounds in serum displayed apparent Michaelis-Menten kinetics. Serum concentrations of base-labile conjugates were similar to parent concentrations for VPA, were an order of magnitude lower than parent concentrations for CCA, and were undetectable for MCCA. Urinary recovery of base-labile (apparently glucuronide) conjugates in the bile-exteriorized rat was 28.8%, 12.0%, and 25.2% of the administered dose for VPA, CCA, and MCCA, respectively. In contrast, more than 50% of the dose for VPA and MCCA was recovered in bile as the base-labile conjugate, with less than 5% of the CCA dose recovered via this excretory route. Bile flow was stimulated significantly by VPA and MCCA, but not by CCA; changes in bile flow correlated with the biliary excretion rate of base-labile conjugates rather than with excretion of the parent compounds themselves.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Determination of vanillylmandelic acid, vanillactic acid, and homovanillic acid in dried urine on filter-paper discs by high-performance liquid chromatography with coulometric electrochemical detection for neuroblastoma screening.

We report a method for determination of vanillylmandelic acid, vanillactic acid, and homovanillic acid by high-performance liquid chromatography (HPLC), with coulometric electrochemical detection, for mass screening of neuroblastoma. Urine samples were collected on filter paper, dried, and then pretreated. The chromatographic procedure is reliable and fast, allowing for a large sample throughput for routine screening. Intricate extraction procedures and centrifugal separation are unnecessary. Screening for neuroblastoma by HPLC is rapidly gaining acceptance in Japan, and our method is being used at many screening centers. Of 26,571 infants screened in one year in Yokohama City, our method detected five with neuroblastoma.

Chromatography, High Pressure Liquid↗
PubMed1984

3-methoxy-4-hydroxyphenylglycol, 5-hydroxyindoleacetic acid, and homovanillic acid in human cerebrospinal fluid. Storage and measurement by reversed-phase high-performance liquid chromatography and coulometric detection using 3-methoxy-4-hydroxyphenyllactic acid as an internal standard.

To simultaneously measure 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5HIAA), and homovanillic acid (HVA) in human cerebrospinal fluid (CSF), we used an acetonitrile protein precipitation, reversed-phase high-performance liquid chromatography with coulometric detection, and 3-methoxy-4-hydroxyphenyllactic acid (MHPLA) as an internal standard for all three metabolites. MHPG, 5HIAA, HVA, and MHPLA were stable for one month when stored in CSF at -70 degrees C. Three determinations were made in triplicate for each of seven subjects over a 30-day storage period and the coefficients of variation within subject for these determinations ranged from 0.075 to 0.165 for MHPG, 0.045 to 0.148 for 5HIAA and 0.053 to 0.181 for HVA. Means and standard deviations of CSF concentrations were 10.7 +/- 3.0 ng/ml for MHPG, 22.4 +/- 9.9 ng/ml for 5HIAA, and 39.9 +/- 21.4 ng/ml for HVA. This method provides simple sample preparation, sensitivity, and cost advantages, as well as simultaneous extraction and quantitation of MHPG, 5HIAA, and HVA using an internal standard.

Chromatography, High Pressure Liquid↗
PubMed1982

Influence of UV- and capsaicin-induced erythema as well as of acetylsalicylic acid on the urinary excretion of vanilmandelic acid and homovanillic acid in man.

In the present study we investigated whether by means of urinary excretion of vanilmandelic acid (VNA) and homovanillic acid (HVA), resp., the two main metabolites of adrenaline, noradrenaline and dopamine, informations could be obtained on synthesis and release of catecholamines in inflammation. UV- and capsaicin-induced erythema, resp., were used as the inflammatory models. The urinary excretion or both VMA and HVA were found to be decreased after UV irradiation. Administration of acetylsalicylic acid during UV irradiation inhibited the decrease of VMA excretion whereas HVA excretion remained low. The application of capsaicin as a plaster failed to influence the urinary VMA and HVA excretion. Our results could be explained on the basis of the interrelationship between catecholamines and prostaglandins. Other possible mechanisms are discussed.

Adult↗
PubMed1980

Spontaneous cholecystocolonic fistula: a model situation for bile acid diarrhea and fatty acid diarrhea as a consequence of a disturbed enterohepatic circulation of bile acids.

Fistulas between the biliary and gastrointestinal tract complicate 12% of cases with cholecystitis. Communications of the biliary tract occur with decreasing frequency into the duodenum, colon and stomach. Clinical symptoms of cholecysto-colonic fistulas are chills and temperature elevation indicating ascending cholangitis. As bile acids bypass the small intestine, diminished fat absorption results. The unusual amount of bile acids in the colon delays water absorption, causing bile acid diarrhea. A pneumocholangiogram is seen in only 50% of the cases. Barium enema will visualize the fistula most often.

Aged↗