Search PubMed⌕ Search

Biomedical subjects

J M Walker

Publications and source records attributed to J M Walker.

At least 271 records · Page 15Linked to original sources
PubMed1980

Purification of glutamate dehydrogenase from ox brain and liver. Evidence that commercially available preparations of the enzyme from ox liver have suffered proteolytic cleavage.

1. A rapid procedure, involving ion-exchange chromatography on DEAE-cellulose and affinity chromatography on GTP-Sepharose, was used to purify glutamate dehydrogenase from ox brain and liver. 2. Preparations purified in this way differed from those of the ox liver enzyme that were obtained from commercial suppliers in their mobilities on polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate. This difference appears to result from the occurrence of limited proteolysis during the preparation of the latter enzyme samples. 3. N-Terminal sequence analysis showed the presence of four amino acid residues in the enzyme prepared in this study that were not present in those obtained from the commercial sources and which have not been reported in previous studies on the sequence of the ox liver enzyme. 4. A preliminary examination of the enzyme prepared in this way indicated that the Michaelis constants for the substrates are similar to those obtained from the commercial preparation, but that the response to allosteric effectors was modified.

Amino Acid Sequence↗
PubMed1980

The isolation of three new high mobility group nuclear proteins.

In addition to the four high mobility group non-histone chromosomal proteins HMG 1, 2, 14 and 17 and histone H1, perchloric acid extracts of nuclei contain a number of other smaller low molecular weight proteins. Three of these proteins (HMG 18, 19A, and 19B) have been purified and characterized. Protein HMG 18 has high lysine and alanine contents, resembling histone H1. Proteins HMG 19A and 19B have high contents of basic and acidic amino acids and resemble HMG proteins 1, 2, 14 and 17. N-terminal sequence analyses of the proteins show that they are not degradation products of histones or the other HMG proteins. However, there are sequence similarities between HMG 18 and histone H5, and between HMG 19B and HMG 17, supporting the view that the HMG proteins and the lysine-rich histones are functionally related.

Amino Acid Sequence↗
PubMed1980

The isolation, characterization and partial sequences of the chicken erythrocyte non-histone chromosomal proteins HMG14 and HMG17. Comparison with the homologous calf thymus proteins.

Non-histone chromosomal proteins HMG14 and HMG17 were isolated from chicken erythrocyte nuclei. The proteins were characterized by amino acid analysis and by N-terminal sequence analyses. Comparison with the corresponding data for the calf thymus proteins shows that 11% of the residues in HMG14 protein and 5% of the residues in HMG17 protein differ between the two species. Proteins HMG14 and HMG17 therefore do not appear to exhibit the evolutionary stability shown by the nucleosome core histones. Detailed evidence for the amino acid sequence data has been deposited as Supplementary Publication SUP 50101 (4 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. 4. (1978) 169, 5.

Amino Acid Sequence↗
PubMed1980

The ontogenesis of sleep states, thermogenesis, and thermoregulation in the Virginia opossum.

Polygraphic recordings of sleep and wakefulness were obtained over 4-hr periods from infant opossums, aged 48-79 days, while they were in the mothers' pouches. Concurrent body temperature measurements were obtained from littermates held at ambient temperatures of 25 and 30 degrees C. The ontogenesis of sleep was similar to that of placental mammals: quiet sleep increased from 13% sleep time at 48 days to 55% at 79 days; conversely, active sleep decreased from 87% to 45%, respectively. the amplitude of the electroencephalogram (EEG) during quiet sleep increased with age and quiet sleep could be categorized as slow wave sleep at 75 days. Active sleep could be identified as rapid eye movement sleep at the same age. Temperature measurements revealed that thermogenesis appeared at approximately 55 days and the 1st signs of thermoregulation were apparent at 67 days. Near-adult thermoregulatory capabilities were present by 79 days. Increases in percent time spent in quiet sleep corresponded with increases in percent adult thermogenesis. The appearance of slow wave EEG activity coincided with the onset of thermoregulatory capabilities. We suggest that lowered metabolism associated with slow wave sleep is adaptive in offsetting the increased energy demands of thermogenesis.

Aging↗
PubMed1980

Behavioral effects of dynorphin 1-13 in the mouse and rat: initial observations.

Dynorphin is a recently identified, pharmacologically potent endogenous opioid peptide. Heretofore it has not been characterized for its behavioral effects. The effects of centrally infused dynorphin upon a variety of behaviors were therefore examined in mice and rats. The present findings point to a specific profile of behavioral activity. The peptide was active in facilitating feeding and grooming, but was inactive in modifying pain sensitivity and rearing behavior. Naloxone was generally ineffective in reversing behavioral effects. Dynorphin thus appears to have some opiate-like effects upon exogenous administration but may be rapidly broken down into a behaviorally potent non-opiate peptide fragment.

Animals↗
PubMed1980

Morphological variants in the human fetal hip joint. Their significance in congenital hip disease.

In a study of 280 hips in 140 normal fetuses, sixty-five of the ninety-two hips of forty-six fetuses between the ages of twelve weeks and term showed morphological variants, yet they were neither subluxated nor dislocated and showed no statistically significant morphological differences from normal joints. The vazriants observed included flattening (fourteen hips) or rounding-off of the rim of the labrum (nine hips), localized dips in the labrum (twenty hips), folding of the labrum (six hips), capsular folds (four hips), extension of the pulvinar pad between the joint surfaces (six hips), and kinking of the ligament of the head of the femur (seven hips). The localization of these variants in the anterosuperior quadrant of the acetabulum was highly significant (p < 0.001), but there was no significant relationship to sex or side of involvement. A significant relationship to age, on the other hand, was evident since the frequency of these minor morphological variations in the fetal hip joint appeared to increase with age. Considering all 140 fetuses, the ones with variant hips formed 55 per cent of all of those older than twenty-eight weeks and only 23 per cent of those younger than twenty-eight weeks (p = 0.007). I suggest that some of these variants are subclinical manifestations of congenital hip disease.

Acetabulum↗
PubMed1979

The isolation and partial sequence of peptides produced by cyanogen bromide cleavage of calf thymus non-histone chromosomal high-mobility-group protein 2. Sequence homology with non-histone chromosomal high-mobility-group protein 1.

Peptides produced by CNBr cleavage of non-histone chromosomal protein HMG 2 (CNBr peptides) were isolated and characterized, and their partial sequences were determined. The present sequence data account for over half of the sequence of the protein HMG (high-mobility-group) 2 molecule, and, together with previously published results, provide interesting information on the charge distribution within the molecule. Comparison of the CNBr-peptide-sequence data for protein HMG 2 with the previously published data on the CNBr peptides from protein HMG 1 reveals extensive sequence homology between the two proteins. Detailed evidence for the amino acid-sequence data has been deposited as Supplementary Publication SUP 50095 (6 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1978) 169, 5.

Amino Acid Sequence↗
PubMed1979

Asthma due to industrial use of chloramine.

Seven brewery workers developed asthmatic symptoms after using chloramine (chloramine-T) powder as a sterilising agent. They gave positive weal and flare reactions to skin-prick tests with solutions of chloramine at strengths that caused no reactions in unexposed controls. The symptoms did not recur once the men had been removed from areas in which chloramine was handled. As well as causing irritant effects, inhaling dry or liquid aerosols of chloramine may cause sensitisation, with workers being prone to allergic asthma on reexposure. In view of this, measures should be taken to ensure that chloramine is not inhaled.

Adult↗
PubMed1979

Sleep and estivation (shallow torpor): continuous processes of energy conservation.

Estivation (shallow torpor) in the round-tailed ground squirrel (Citellus tereticaudus) is entered through electrophysiologically defined states of sleep. Rapid-eye-movement sleep diminishes as body temperature falls in such a way that, at a body temperature of 26 degrees to 28 degrees C, torpor is characterized by almost continuous slow-wave sleep isomorphic with that observed at euthermic body temperatures.

Animals↗