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S C Allen

Publications and source records attributed to S C Allen.

At least 19 recordsLinked to original sources
PubMed2000

Multiple histone acetyltransferases are associated with a chicken erythrocyte chromatin fraction enriched in active genes.

We have examined salt-soluble chromatin released by micrococcal nuclease from a 15-day-old chicken embryo erythrocyte nuclei for histone acetyltransferase (HAT) activities. This chromatin is enriched in transcriptionally active sequences from within the active beta-globin locus and contains elevated levels of acetylated core histones. HAT activities present in this fraction target histones H4, H3, and H2A when the chromatin itself is used as the substrate. In gel HAT activity assay demonstrates that the salt-soluble chromatin fraction contains four acetyltransferase molecules distinguished by their different molecular masses (47, 33, 32, and 28 kDa). Further separation of the chromatin by centrifugation through sucrose gradients shows that the acetyltransferases segregate into chromatin-bound and chromatin-free populations. The 32- and 28-kDa HATs are associated with chromatin, whereas the 47- and 33-kDa HAT molecules are not. The chromatin-bound HAT activities predominantly target H4 to give the diacetyl and triacetyl species; some acetylation of H2A can also be seen. Our results suggest that the chromatin-associated acetyltransferases have a role in gene regulation.

Acetylation↗
PubMed1999

Refined crystal structures of native human angiogenin and two active site variants: implications for the unique functional properties of an enzyme involved in neovascularisation during tumour growth.

Human angiogenin (Ang), an unusual member of the pancreatic RNase superfamily, is a potent inducer of angiogenesis in vivo. Its ribonucleolytic activity is weak (10(4) to 10(6)-fold lower than that of bovine RNase A), but nonetheless seems to be essential for biological function. Ang has been implicated in the establishment of a wide range of human tumours and has therefore emerged as an important target for the design of new anti-cancer compounds. We report high-resolution crystal structures for native Ang in two different forms (Pyr1 at 1.8 A and Met-1 at 2.0 A resolution) and for two active-site variants, K40Q and H13A, at 2.0 A resolution. The native structures, together with earlier mutational and biochemical data, provide a basis for understanding the unique functional properties of this molecule. The major structural features that underlie the weakness of angiogenin's RNase activity include: (i) the obstruction of the pyrimidine-binding site by Gln117; (ii) the existence of a hydrogen bond between Thr44 and Thr80 that further suppresses the effectiveness of the pyrimidine site; (iii) the absence of a counterpart for the His119-Asp121 hydrogen bond that potentiates catalysis in RNase A (the corresponding aspartate in Ang, Asp116, has been recruited to stabilise the blockage of the pyrimidine site); and (iv) the absence of any precise structural counterparts for two important purine-binding residues of RNase A. Analysis of the native structures has revealed details of the cell-binding region and nuclear localisation signal of Ang that are critical for angiogenicity. The cell-binding site differs dramatically from the corresponding regions of RNase A and two other homologues, eosinophil-derived neurotoxin and onconase, all of which lack angiogenic activity. Determination of the structures of the catalytically inactive variants K40Q and H13A has now allowed a rigorous assessment of the relationship between the ribonucleolytic and biological activities of Ang. No significant change outside the enzymatic active site was observed in K40Q, establishing that the loss of angiogenic activity for this derivative is directly attributable to disruption of the catalytic apparatus. The H13A structure shows some changes beyond the ribonucleolytic site, but sites involved in cell-binding and nuclear translocation are essentially unaffected by the amino acid replacement.

Amino Acid Sequence↗
PubMed1999

Crystal structure of a hybrid between ribonuclease A and bovine seminal ribonuclease--the basic surface, at 2.0 A resolution.

A variant of bovine pancreatic ribonuclease A has been prepared with seven amino acid substitutions (Q55K, N62K, A64T, Y76K, S80R, E111G, N113K). These substitutions recreate in RNase A the basic surface found in bovine seminal RNase, a homologue of pancreatic RNase that diverged some 35 million years ago. Substitution of a portion of this basic surface (positions 55, 62, 64, 111 and 113) enhances the immunosuppressive activity of the RNase variant, activity found in native seminal RNase, while substitution of another portion (positions 76 and 80) attenuates the activity. Further, introduction of Gly at position 111 has been shown to increase the catalytic activity of RNase against double-stranded RNA. The variant and the wild-type (recombinant) protein were crystallized and their structures determined to a resolution of 2.0 A. Each of the mutated amino acids is seen in the electron density map. The main change observed in the mutant structure compared with the wild-type is the region encompassing residues 16-22, where the structure is more disordered. This loop is the region where the polypeptide chain of RNase A is cleaved by subtilisin to form RNase S, and undergoes conformational change to allow residues 1-20 of the RNase to swap between subunits in the covalent seminal RNase dimer.

Endoribonucleases↗
PubMed1997

Competence thresholds for the use of inhalers in people with dementia.

METHODS: the ability to learn three inhaler techniques of increasing levels of complexity was studied in 50 normal and demented inhaler-naive elderly people (mean age 81 years) with stable 10-point mini-mental test scores (MTS). There were 10 subjects in each of the following groups: MTS 8-10 (non-demented), MTS 7 (borderline), MTS 6 (mild dementia), MTS 5 and MTS 4 (2 moderate dementia groups). The techniques were taught on one day and reassessed on the following day on consecutive days in ascending order of complexity. RESULTS: those with an MTS of 4 were unable to learn any of the techniques, while all the non-demented people could learn all three techniques. For the five-stage technique (standard metered dose inhaler) the 0% threshold (i.e. when none of the subjects was able to learn) was MTS 6, the 50% threshold (at least half but not all could learn) MTS 7 and the 100% threshold (all could learn) MTS 8. For the four-stage technique (inhaler with large spacer) the 0% threshold was MTS 5, the 50% threshold MTS 6 and the 100% threshold MTS 8. For the three-stage technique (inspiration-triggered inhaler) the 0% threshold was MTS 4, the 50% threshold MTS 5 and the 100% threshold MTS 7. CONCLUSIONS: MTS can be used to determine the likelihood of a mild or moderately demented patient being able to learn a multiple-stage inhaler technique.

Aged↗
PubMed1997

A study of autonomic cardiovascular reflexes in elderly patients with pneumonia.

People recovering from pneumonia are often weak for no apparent reason. Clinical features such as postural hypotension, arrhythmia and syndrome of inappropriate ADH have, in other circumstances, been attributed to impaired autonomic function. The aim of this study was to see whether elderly patients with pneumonia had impaired autonomic cardiovascular reflexes and, if so, how long this persisted. We compared healthy elderly controls, elderly controls with trauma (fractured femoral neck) and elderly patients with pneumonia. Thirty-eight subjects were studied in a series of cardiovascular autonomic function tests. Results suggest that elderly people have a high prevalence of impaired cardiovascular autonomic reflexes in the immediate post-pneumonic phase, and that this improves significantly after six weeks, with a further improvement by six months. Elderly patients recovering from pneumonia are predisposed to the adverse effects of drugs and other factors which can further impair autonomic cardiovascular reflexes.

Aged↗
PubMed1994

Crystal structure of human angiogenin reveals the structural basis for its functional divergence from ribonuclease.

Angiogenin, a potent inducer of neovascularization, is the only angiogenic molecule known to exhibit ribonucleolytic activity. Its overall structure, as determined at 2.4 A, is similar to that of pancreatic ribonuclease A, but it differs markedly in several distinct areas, particularly the ribonucleolytic active center and the putative receptor binding site, both of which are critically involved in biological function. Most strikingly, the site that is spatially analogous to that for pyrimidine binding in ribonuclease A differs significantly in conformation and is "obstructed" by glutamine-117. Movement of this and adjacent residues may be required for substrate binding to angiogenin and, hence, constitute a key part of its mechanism of action.

Amino Acid Sequence↗
PubMed1994

A comparison of the predicted and X-ray structures of angiogenin. Implications for further studies of model building of homologous proteins.

The three-dimensional structure of human angiogenin has been determined by X-ray crystallography and is compared here with an earlier model which predicted its structure, based on the homology of angiogenin with bovine pancreatic ribonuclease A. Comparison of the predicted model and crystal structure shows that the active-site histidine residues and the core of the angiogenin molecule, including most of the beta-strands and alpha-helices, were predicted reasonably well. However, the structure of the surface loop regions and residues near the truncated C-terminus differs significantly. The C-terminal segment includes the active-site residues Asp-116, Gln-117, and Ser-118; Gln-117 in particular has been shown to be important in affecting the ribonucleolytic activity of angiogenin. Also, the orientation of one helix in the model differed from the orientation observed experimentally by about 20 degrees, resulting in a large displacement of this chain segment. The difficulty encountered in predicting the surface loop regions has led to a new algorithm [Palmer and Scheraga (1991), J. Comput. Chem., 12, 505-526; (1992), J. Comput. Chem., 13, 329-350] for predicting the conformations of surface loops.

Amino Acid Sequence↗
PubMed1991

Purification, characterisation and mutagenesis of highly expressed recombinant yeast pyruvate kinase.

Recombinant yeast pyruvate kinase has been purified from a strain of Saccharomyces cerevisiae expressing the enzyme to very high levels. Expression was from a multicopy plasmid under the control of the yeast phosphoglycerate kinase promoter. The gene was expressed in the absence of the genomically encoded pyruvate kinase, using a strain of yeast in which the pyruvate kinase gene has been disrupted by the insertion of the yeast Ura3 gene. The purification procedure minimised proteolytic artefacts and enabled the convenient purification of 15-20 mg enzyme from 11 culture. The purified enzyme was characterised by a high specific activity and by a lack of proteolytic degradation. Two active-site mutants of yeast pyruvate kinase have been produced, expressed and characterised in this system and preliminary results are described.

Chromatography, Gel↗
PubMed1990

Anorexia nervosa in the elderly: a case report and review of the literature.

Anorexia nervosa is a rare disorder in the elderly but should be thought of in the differential diagnosis of extreme weight loss, especially if there are accompanying psychological features and normal baseline investigations. Psychiatric opinion should be obtained and treatment, although of unproven value, considered, since improvement may increase mobility and reduce morbidity and mortality.

Aged↗
PubMed1989

The relation between height, armspan and forced expiratory volume in elderly women.

Loss of height occurs with ageing. This could distort the relation between height and forced expiratory volume in 1s (FEV1) as age increases. Armspan, which approximates to height at maturity, does not fall with age and might, therefore, be a better linear variable to compare with age and spirometric volumes in older people. We studied the relation between age, height, armspan and FEV1 in 150 women aged 60-91 years. The mean value of span minus height was 4.7 cm (range -5 to +17). Standardized FEV1 (SD) in 5-year age bands between 60 and 80+ fell as follows: 1.79(0.52)1, 1.62(0.49)1, 1.38(0.41)1, 1.32(0.44)1, 1.15(0.48)1. When re-standardized using armspan, the values were: 1.76(0.48)1, 1.59(0.53)1, 1.37(0.46)1, 1.29(0.47)1, 1.11(0.54)1. The differences between the two standardized values in each age band were not significant. It was concluded that span measurements offer no advantage over height measurements in cross-sectional population studies of lung volume in old age. However, in subjects who cannot have their height measured, or who are known to have lost a substantial amount of height, armspan is a reasonable substitute measure of body size from which to calculate predicted FEV1 values.

Aged↗
PubMed1989

Ambulatory electrocardiography in the elderly: an audit.

In a retrospective analysis of 264 episodes of ambulatory electrocardiography (AECG) in 252 elderly out-patients the overall diagnostic yield was only 12 per cent. However, AECG was found to be of significant value in detecting symptomatic tachyarrhythmias, and in confirming the diagnosis of the 'sick sinus syndrome'. The AECG results influenced the management plan in at least 16 per cent, and changes in drug treatment in 10 per cent. When interpreted critically, AECG is useful tool in the investigation of elderly patients with symptoms such as syncope, faintness, dizziness and unexplained falls.

Aged↗
PubMed1988

Clinical prognostic indices of fatality in elderly patients admitted to hospital with acute pneumonia.

Acute pneumonia in the elderly is a common and serious condition. The importance of key clinical features and physical signs presenting to the junior hospital doctor was prospectively assessed in 100 consecutive patients admitted acutely to two hospitals. The most significant finding is that elderly patients with pneumonia who are found to be acutely confused at the time of presentation or who gave a previous history of chronic brain failure are much more likely to die than others. Thus such patients should be assessed with particular attention to the early diagnosis and vigorous treatment of pneumonia.

Acute Disease↗
PubMed1986

What determines whether an elderly patient can use a metered dose inhaler correctly?

The metered dose inhaler (MDI) technique of 30 elderly patients (mean age 79.9 years) was assessed. Sixty per cent were competent, though only 10% had an ideal technique; 40% were incompetent. Inadequate timing of actuation and inhalation was the most frequent error made. Competence was significantly related to mental status questionnaire (MSQ) scores of 7/10 or more. Patients who were first prescribed an MDI in hospital were significantly more likely to be competent than those prescribed an MDI by the general practitioner. Competence was not related to age, underlying diagnosis or duration of MDI therapy. Elderly patients requiring MDI therapy should be carefully selected and properly instructed by the prescribing doctor.

Aerosols↗
PubMed1986

Osteoid osteoma in a cervical pedicle. Resection via transpillar approach.

Lesions in the pedicles of the cervical spine are both a diagnostic and technical challenge. An osteoid osteoma of the pedicle of the fourth cervical vertebra occurred in a 17-year-old girl. Resection of the tumor adjacent to the dura medially and the vertebral artery anterolaterally was accomplished via a transpillar approach. The transosseus approach preserved the facet joints and posterior elements and obviated the need for an interbody fusion.

Adolescent↗