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Biomedical subjects

D H Williams

Publications and source records attributed to D H Williams.

At least 127 records · Page 7Linked to original sources
PubMed1988

Analysis of the in vivo phosphorylation state of rabbit skeletal muscle glycogen synthase by fast-atom-bombardment mass spectrometry.

The in vivo phosphorylation state of glycogen synthase was re-examined by fast-atom-bombardment mass spectrometry and a procedure in which phosphoserine residues are first converted to S-ethylcysteine. In animals injected with the beta-adrenergic antagonist propranolol, the phosphorylation sites in the N-terminal (N) and C-terminal (C) cyanogen bromide peptides were identified as the serine residues at N7, the region C28-C39, C42, C46 and C100. In animals injected with adrenalin, the phosphorylation of N7 increased from 0.6 to 0.8 mol/mol, the region C28-C39 from 0.7 to 1.2 mol/mol and C100 from 0.3 to 0.6 mol/mol. The phosphorylation states of C42 (0.7 mol/mol) and C46 (0.9 mol/mol) were unchanged. In addition, two further serine residues became phosphorylated at positions N10 (0.5 mol/mol) and C87 (0.5 mol/mol), which were not phosphorylated in the absence of adrenalin. Residues N10 and C42 have not been recognized as in vivo sites of phosphorylation previously. The results suggest that N10 is phosphorylated by a novel protein kinase which may be activated by cyclic-AMP-dependent protein kinase. The phosphorylation of C42 is likely to be catalysed by glycogen synthase kinase 3. The protein kinases responsible for phosphorylating N7, the region C28-C39, C46, C87 and C100 in vivo and the molecular mechanisms by which adrenalin inactivates glycogen synthase in vivo are discussed. Residue N3, a major site phosphorylated by casein kinase-I in vitro is not phosphorylated in vivo. This and other evidence indicates that casein kinase-I is not a glycogen synthase kinase in vivo.

Animals↗
PubMed1988

The cDNA sequence coding for prepro-PGS (prepro-magainins) and aspects of the processing of this prepro-polypeptide.

Amphibian skin is well known as a source of peptides homologous to bioactive peptides found in mammalian gut and brain. A systematic investigation of the skin secretions from Xenopus laevis revealed several peptides not derivable from known precursors. The sequence elucidation, utilizing fast atom bombardment/mass spectrometry, of two peptides, PGS and PGS Gly-10;Lys-22, is reported. These have been independently characterized and named magainins and found to have antimicrobial activity. A mixed sequence oligonucleotide probe complementary to the mRNA sequence coding for PGS was synthesized and used to screen a Xenopus skin cDNA library. A full length cDNA species encoding prepro-PGS was isolated and characterized, and its sequence is reported. The deduced precursor sequence was found to contain one copy of PGS Gly-10;Lys-22 and five copies of PGS. The proteolytic processing of this prepro-polypeptide is discussed.

Amino Acid Sequence↗
PubMed1988

Levitide, a neurohormone-like peptide from the skin of Xenopus laevis. Peptide and peptide precursor cDNA sequences.

A novel peptide, levitide, less than Glu-Gly-Met-Ile-Gly-Thr-Leu-Thr-Ser-Lys-Arg-Ile-Lys-Gln-NH2 has been isolated from skin secretions of the South African frog Xenopus laevis and sequenced by fast atom bombardment mass spectrometry. Synthetic oligonucleotides were used as probes to screen a X. laevis skin cDNA library for species coding for preprolevitide. Two such clones were detected and their sequences are reported here. Preprolevitide is 88 residues long, exhibits a putative signal sequence at the amino terminus, and contains the levitide peptide at the carboxyl terminus. The levitide precursor shows a striking nucleotide and amino acid (86%) sequence homology with the precursor of xenopsin, a biologically active octapeptide from Xenopus skin, and also encodes a 25-residue amphipathic peptide that is released by processing at a single arginine residue.

Amino Acid Sequence↗
PubMed1988

Formaldehyde adducts of glutathione. Structure elucidation by two-dimensional n.m.r. spectroscopy and fast-atom-bombardment tandem mass spectrometry.

Aqueous mixtures of formaldehyde and glutathione react to form a variety of cyclized adducts in addition to S-hydroxymethylglutathione. The adducts are in labile equilibrium with each other and are not readily separated. The structures of two of the other major adducts were determined by concerted application of 13C-1H two-dimensional chemical-shift correlation, fast-atom-bombardment mass spectrometry and tandem mass spectrometry to the adduct mixtures in aqueous solution.

Chemical Phenomena↗
PubMed1988

Forces in molecular recognition: comparison of experimental data and molecular mechanics calculations.

NMR studies of the rotation barrier of the disaccharide of the glycopeptide antibiotic vancomycin have been used to test the performance of computer simulation techniques using molecular mechanics. In the absence of any solvated water, no correlation could be found between experiment and calculation. By introducing solvent water molecules into the binding region of the antibiotic, the NMR results could be simulated both qualitatively and quantitatively within experimental error without using massive computational resources.

Binding Sites↗
PubMed1988

Structural elucidation of N-terminal post-translational modifications by mass spectrometry: application to chicken enolase and the alpha- and beta-subunits of bovine mitochondrial F1-ATPase.

Peptides generated from enzymatic hydrolysis of chicken enolase and the alpha- and beta-subunits of bovine F1-ATPase were analyzed by mass spectrometry to determine the nature of their modified N-termini. In the case of chicken enolase, a peptide was isolated from a Staphylococcus aureus proteinase digest by HPLC and analyzed directly by fast atom bombardment mass spectrometry (FABMS). In conjunction with mass spectral evidence obtained from the methyl ester derivative and a secondary tryptic peptide, a structure is proposed containing an N-acetyl serine at the N-terminus. The alpha-subunit of bovine mitochondrial ATPase was chromatographed by HPLC after S. aureus proteinase digestion and a single peak was analyzed on the basis of predicted retention times. A Mr 716 was determined by FABMS and pyrrolidone carboxylic acid was deduced on the basis of its amino acid composition and partial Edman sequence data. The beta-subunit of ATPase produced a series of closely eluting peaks on HPLC after limited digestion with trypsin of the alpha 2 beta 2 complex. These peptides were analyzed by both Edman degradation and FABMS. These data showed the N-terminus to be frayed with N-terminal sequences beginning in pyro-Glu-Ala-Ser, Gln-Ala-Ser, Glu-Ala-Ser, Ala-Ser, and Ser but with no N-acetyl-Ser as was previously thought.

Amino Acid Sequence↗
PubMed1988

Operations to restore elbow flexion after brachial plexus injuries.

We have reviewed 50 patients at a mean period of 2.7 years after operations to restore elbow flexion lost as a result of traction injuries of the brachial plexus. A variety of operations were used and, in general, patient satisfaction was high. Objectively, however, the power in the transferred muscles was poor; less than half of the patients had a significant improvement in function. Poor control of the shoulder often compromised the result. Latissimus dorsi and triceps transfers proved most reliable, and some Steindler flexorplasties also gave satisfactory results. Pectoralis major transfers were disappointing and we do not recommend their use in women.

Adolescent↗
PubMed1988

Sustained attention and information processing speed in chronic survivors of severe closed head injury.

Sustained attention and information processing speed in 15 long-term survivors of severe closed head injury and 14 demographically matched controls have been examined. The average time between head injury and testing was 3.6 years. The performance of patients on all tasks was impaired relative to controls, thus documenting persistent deficits in attention. Of particular interest was the finding that controls were capable of redirecting and improving their sustained attention during a test session versus the steady decline in patient performance. The findings are discussed within the framework of controlled attentional processes.

Adult↗
PubMed1987

Observations on the quantitation of the phosphate content of peptides by fast-atom bombardment mass spectrometry.

Equimolar mixtures of the phosphorylated and dephosphorylated forms of several peptides have been subjected to fast-atom bombardment mass spectrometry (FABMS), to investigate whether the stoichiometry of phosphorylation can be determined from the relative molecular-ion abundances of the phospho and dephospho derivatives. It is concluded that quantitation can be achieved for peptides with large positive or negative hydrophobicity/hydrophilicity indices (delta F values) where addition of a phosphate group does not alter the distribution of the peptide within the matrix significantly. For peptides with small positive or negative delta F values, phosphopeptides tend to be partially suppressed by their dephosphorylated counterparts. Suppression can be partially or totally overcome by conversion of the peptide to a hydrophobic derivative, and by the selection of an appropriate matrix. Alternatively, addition of a very strong acid, perchloric acid, can even reverse the original suppression effect. This last effect is believed to be due to the increased ionic strength in the matrix, which forces a relatively hydrophilic analyte to the matrix surface; and the ability of such a phosphorylated analyte to form a more stable gas-phase cation.

Chemical Phenomena↗
PubMed1987

Biosynthesis and degradation of peptides derived from Xenopus laevis prohormones.

Peptides present in the skin secretion of the South African frog, Xenopus laevis, have been analysed by fast atom bombardment mass spectrometry and h.p.l.c. in the mass range 500-3200 Da. We have investigated the effects of successive glandular secretions induced by noradrenaline injections on these peptide levels and have found that the replenishment of the whole range of peptides is complete within 2-6 days. Intact secretory vesicles free of cellular contaminants contain a relatively large number of peptides with molecular masses in the range 2400-2700 Da. We have termed these peptides primary products or spacer peptides, since they originate from spacer regions of the precursors to xenopsin and caerulein. However, if the secretory vesicles are disrupted during the collection procedure and the solution containing the secretion is kept at room temperature for up to 2 h, relatively little of the larger peptides remain. By comparing the relative levels of the various peptides present in these secretions we have found that the larger peptides are proteolytically cleaved into smaller fragments by a novel cleavage at the N-terminal side of a lysine residue (at Xaa-Lys bonds where Xaa is Leu, Gly, Ala or Lys). Preliminary evidence has been obtained suggesting that the larger intact peptides possess lytic activity whereas the smaller proteolytic fragments appear relatively inactive. This may represent a mechanism by which the secretions are rendered harmless to the frog itself, since prolonged exposure would be expected to result in toxic effects. The dorsal glands of X. laevis thus appear similar to endocrine glands, since they are involved in peptide biosynthesis, secretion and subsequent proteolytic degradation.

Amino Acid Sequence↗
PubMed1987

Magnetic resonance imaging and computerized tomography in relation to the neurobehavioral sequelae of mild and moderate head injuries.

Twenty patients admitted for minor or moderate closed-head injury were studied to investigate the relationship between magnetic resonance imaging (MRI) and neurobehavioral sequelae. The MRI scans demonstrated 44 more intracranial lesions than did concurrent computerized tomography (CT) scans in 17 patients (85%); most of these lesions were located in the frontal and temporal regions. Estimates of lesion volume based on MRI were frequently greater than with CT; however, MRI disclosed no additional lesions that required surgical evacuation. Neuropsychological assessment during the initial hospitalization revealed deficits in frontal lobe functioning and memory that were related to the size and localization of the lesions as defined by MRI. Follow-up MRI and neuropsychological testing at 1 month (13 cases) and 3 months (six cases) disclosed marked reduction of lesion size paralleled by improvement in cognition and memory. These findings encourage further investigation of the prognostic utility of MRI for the clinical management and rehabilitation of mild or moderate head injury.

Adolescent↗
PubMed1986

Novel peptide fragments originating from PGLa and the caerulein and xenopsin precursors from Xenopus laevis.

Skin secretions from the South African frog Xenopus laevis have been chromatographed by high performance liquid chromatography (HPLC), fractionated, and analyzed by fast atom bombardment-mass spectrometry (FAB-MS). The HPLC chromatograms showed the secretion to be a complex mixture with over 30 components at similar levels to the four peptides previously isolated from X. laevis skin, i.e. xenopsin, caerulein, thyrotropin-releasing hormone, and PGLa. FAB-MS analysis of the HPLC fractions gave numerous protonated molecular ions ranging from m/z 491 to 2662. Preliminary assignments of these components were made by comparing these experimental molecular weights to those predicted for regions within the xenopsin, caerulein, thyrotropin-releasing hormone, and PGLa precursors. These results suggested that many of these skin secretions were peptides originating from additional processing of the xenopsin, caerulein, and PGLa precursors, primarily involving cleavage at single arginine residues, and a novel cleavage at the NH2-terminal side of single lysines. These assignments were subsequently confirmed by Edman degradation, FAB-MS peptide sequencing, and amino acid analysis. All of these peptides contain one or more lysines and would be expected to have amphiphilic structures. As yet, nothing is known about their activity, although they resemble in composition the mast cell degranulating peptides melittin and the bombolitins. These precursor fragments were also found to have limited sequence homology to bombinin, a hemolytic amphibian peptide isolated from the European Bombina toad.

Amino Acid Sequence↗
PubMed1986

The frayed N-terminal of the inhibitor protein of bovine mitochondrial F1-ATPase.

The N-terminal region of the bovine mitochondrial F1-ATPase inhibitor protein is frayed. In three independently isolated samples about 62% of chains start at glycine-1. A further 22% of chains start at residue 2, serine, and the remainder at residue 3, glutamic acid. No evidence can be found for alpha-N-formylglycine reported previously. The fraying may be a consequence of proteolytic processing of the precursor of the inhibitor protein during entry into the mitochondrion.

Amino Acid Sequence↗
PubMed1986

A long-term study following Bennett's fracture.

Twenty-five patients with documented Bennett's Fractures were reviewed five to sixteen years following injury (Mean 9.6 years). The majority of fractures affected the dominant hand and occurred in males. Twenty-two patients were managed conservatively by plaster immobilisation. At review ten patients were asymptomatic and only two had significant symptoms. Examination revealed loss of movement in the trapeziometacarpal joint of the thumb in twenty-one cases. Five of these exhibited malrotation of the thumb. Review of the post reduction radiographs revealed separation of the fragments by 1 mm or more in sixteen patients, but symptoms at follow-up could not be correlated with accuracy of reduction. Twenty-three patients had a varus angulation of the first metacarpal base which could be correlated to the initial post-reduction displacement. There was no correlation with the restriction of movement. Although metacarpal length will only be maintained by reduction of the fracture, there was little evidence that imperfect reduction leads to significant symptomatic arthritis in the long term.

Adolescent↗
PubMed1986

Training responses of two age groups during treadmill walking.

The purpose of the present study was to use a previously developed treadmill walking test to determine training-induced changes within and between two groups of untrained men during a six week training period. One group consisted of seven middle-aged (mean age, 41.3 yr), and the second group consisted of seven young adult (mean age, 19.9 yr), men. Heart rates following training were significantly lower at all work intensities for the middle-aged men (p less than 0.005) whilst for the young adults only the 12.5% and 15% (p less than 0.025) work levels were significantly lower. Blood lactic acid concentrations (p less than 0.005), Respiratory Exchange Ratios (p less than 0.05), Ventilatory Equivalents (p less than 0.005) and mean Two Mile times (p less than 0.005) were all significantly lower after training for the older age group but this was not so for the younger adult group. The oxygen cost of the walking test was lower for four of the workloads of the middle-aged, but only for the final workload (p less than 0.005) for the young adults, after training. The performance test did not disadvantage the middle-aged subjects yet the results demonstrated that the test provided a common means of reflecting the training state of the two groups whether the level of activity took place on the treadmill or on the track.

Adolescent↗