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N E MacKenzie

Publications and source records attributed to N E MacKenzie.

25 records · Page 2Linked to original sources
PubMed1988

Determination of local conformational stability in fragment 96-133 of bovine growth hormone by high-resolution H NMR spectroscopy.

The specific assignment of resonances in the 400-MHz nuclear magnetic resonance (NMR) spectrum of fragment 96-133 (AII) of bovine growth hormone (bSt) is described. Assignments have been made with homonuclear two-dimensional techniques, in particular that of sequential resonance assignment. Complete assignments were possible for the spin systems of 16 residues out of a total of 38 and partial assignments for another 5. Assignment of resonances to either residue type or a class of residue was possible for a number of other spin systems. Analysis of the type of nuclear Overhauser effect (NOE) indicates that segments 96-110 and 130-133 are nonregular stable structures and that the segment 111-127, which putatively spans the alpha-helix, is not sufficiently stable to generate NOEs.

Amino Acid Sequence↗
PubMed1988

Preferred conformational state of the N-terminus section of a bovine growth hormone fragment (residues 96-133) in water is an omega loop.

The solution structure of a 38-amino-acid-residue, biologically active fragment of bovine growth hormone (bGH96-133) was investigated with a combined nuclear magnetic resonance (NMR) and computer modeling approach. With the distance geometry program DISGEO and distance constraints derived from nuclear Overhauser enhancement (NOE) experiments, it was found that residues Ser-100 to Tyr-110 circumscribe and omega-loop, a recently categorized feature of nonregular secondary protein structure.

Amino Acid Sequence↗
PubMed1988

Structural and immunochemical aspects of Brucella abortus endotoxins.

Smooth lipopolysaccharide (sLPS) of Brucella abortus, which is the most immunodominant component among the antigens of B. abortus isolated, has been used for diagnosis for decades. High yields of sLPS can be prepared by a modification of the procedures of Moreno et al. (J. Bacteriol. 138:361-369, 1979). Washed B. abortus cells can be disrupted by 21 freeze-quick thaw cycles and ultrasonication to separate non-membrane-bound material; then phenol extraction is performed 3 times and the phenol fraction is washed with H2O intensively. The membrane-bound sLPS can be fractionated into 3 to 5 groups according to the extent of dialysis and centrifugation. These membrane bound sLPS fractions show marked individual differences in their precipitin profile and chemical composition. Their protein content varies from 16% to 42% as determined by dye binding test and 17 to 60% by Lowry phenol method using bovine serum albumin as the standard, which indicates that these proteins associated with LPS may play important roles in the immunochemical interactions, solubility, and the heterogeneity of B. abortus lipopolysaccharides. Compared to previously published methods, a higher yield of sLPS, ranging from 3.6% to 7.7% of dried bacteria, is obtained. Group f5A, which has a standard bell shaped curve in the precipitin assay, is one of the major fractions in all three strains (1119.3, 19, 2308). The protein free sLPS (less than 1% of Lowry reactive component) can be prepared by pronase digestion. The immunochemical reactivity remains about the same before and after this treatment. The O-chains of the major fraction (f5A) of B. abortus (Strains 2308 and 19) membrane bound smooth lipopolysaccharide (sLPS) are obtained by hydrolysis of f5A native sLPS in 1% acetic acid at 100 degrees C for 2 hours. After hydrolysis, the O-chains are separated from the lipid A protein complex by centrifugation, and from small fragments by ultrafiltration of a molecular weight cut-off (MWCO) of 1.0 x 10(3). These carbohydrate haptens can be identified by precipitin-inhibition assay and further fractionated by both membrane filtration and dialysis. The size distributions of carbohydrate haptens of the endotoxins (f5A) ranged from several oligosaccharides up to 1.0 x 10(4) MWCO. Three major fractions of MWCO 8.0-10.0 x 10(3), 3.5-5.0 x 10(3), and less than 1.0 x 10(3) for both strains 2308 and 19 contain more than 85% of the total immunreactive materials.(ABSTRACT TRUNCATED AT 400 WORDS)

Brucella abortus↗
PubMed1981

Control of porphyrin biosynthesis in Rhodopseudomonas spheroides and Propionibacterium shermanii. A direct 13C nuclear-magnetic-resonance spectroscopy study.

The facultative anaerobes Rhodopseudomonas spheroides and Propionibacterium shermanii were grown under anaerobic and aerobic conditions. The effect of light was studied with the photosynthetic R. spheroides, and the adaptation of both species to dark anaerobic life was monitored by direct observation of 5-amino[5-13C]laevulinic acid metabolism by using 13C nuclear-magnetic-resonance spectroscopy.

Aerobiosis↗
PubMedDate not supplied

Reactions of arsenic(III) and arsenic(V) species with glutathione.

Arsenic is metabolized by living systems using oxidation-reduction and methylation reactions, and reduced glutathione (GSH) has been shown to be important in that metabolism. In this study, the solution reactions between GSH and arsenate, arsenite, and their methylated metabolites, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), were characterized using 1H and 13C NMR under a nitrogen atmosphere. Binding to GSH through the thiol group was primarily followed by shifts in the carbon atom bonded to the sulfhydryl group of the cysteinyl residue, i.e., the CH2 carbon atom and the protons bonded to it. The methylated metabolites also showed shifts in the methyl groups attached to the arsenic atom after reaction with GSH. Sodium arsenite, As(III), bound to GSH to form an As(SG)3 complex in solution as indicated by NMR spectra. The identity of the complex was confirmed by FAB-MS after isolation of the compound. Mixtures of sodium arsenate, As(V), and GSH showed that arsenate oxidized GSH in D2O solutions at pH 7 to form oxidized glutathione (GSSG). When the molar ratio of As:GSH exceeded 1:2, evidence for the formation of As(SG)3 was observed. MMA and DMA are both As(V) species, and mixtures with GSH showed oxidation to GSSG initially followed by formation of CH3.As(SG)2 and (CH3)2.As.SG, respectively. The effects of GSH on arsenic metabolism may result from direct reactions between the two compounds.

Arsenates↗
PubMedDate not supplied

Identification and comparison of the urinary metabolites of [1,2,3-13C3]acrylic acid and [1,2,3-13C3]propionic acid in the rat by homonuclear 13C nuclear magnetic resonance spectroscopy.

Acrylic acid (AA) and its esters are used extensively for the production of a variety of polymers. Despite their ubiquitous nature, little has been reported on the metabolism of the parent acid. The metabolites of AA may be volatile, unstable, polar, and thus difficult to isolate. Therefore, 13C NMR was used to help identify and compare directly the urinary metabolites of both 99% 13C-enriched AA and propionic acid (PA). Male Sprague-Dawley rats received [1,2,3-13C]AA (400 mg/kg in water p.o.) or an equimolar dose of [1,2,3-13C]propionate together with a radioactive tracer, [2,3-14C]AA, or [1-14C]propionate, respectively, and excreta were collected for 72 hr. For both acids, expiration of 14CO2 was the major route of elimination of radiolabel (approximately 80%). Approximately 6% of the dose was excreted in the urine. Urine was analyzed directly using proton-decoupled 13C and two-dimensional 13C homonuclear correlated NMR spectroscopy. The urine from AA-treated rats revealed major signals, the intensity of which was time-dependent, from at least five 13C-enriched metabolites of AA. Signals have been assigned to 3-hydroxypropionic acid, N-acetyl-S-(2-carboxyethyl)cysteine, and N-acetyl-S-(2-carboxyethyl)cysteine-S-oxide by comparison with spectra of authentic standards. No unchanged AA was detected. In contrast, the spectra of urine from a propionate-treated rat revealed only a few minor 13C-enriched signals that were assigned to methylmalonic acid. No unchanged PA was detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylates↗