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Biomedical subjects

J Stackhouse

Publications and source records attributed to J Stackhouse.

At least 19 recordsLinked to original sources
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↗
PubMed1998

Redesigning nucleic acids.

A research program has applied the tools of synthetic organic chemistry to systematically modify the structure of DNA and RNA oligonucleotides to learn more about the chemical principles underlying their ability to store and transmit genetic information. Oligonucleotides (as opposed to nucleosides) have long been overlooked by synthetic organic chemists as targets for structural modification. Synthetic chemistry has now yielded oligonucleotides with 12 replicatable letters, modified backbones, and new insight into why Nature chose the oligonucleotide structures that she did.

Catalysis↗
PubMed1998

Speech processing abilities in children with speech vs speech and language difficulties.

This paper reports on the speech processing skills of a group of four year old children with specific speech difficulties and examines the impact of an additional language impairment on these skills. Forty seven children with speech difficulties were tested on two speech output measures and one speech input measure to assess the accuracy of their phonological representations. Their performance was compared to a matched control group n = 47 and analysed according to the presence/absence of an additional language impairment. It was found that children with both speech and language difficulties had poorer speech processing abilities compared to both the normal controls and the children with speech-only difficulties. The clinical implications of these findings are outlined.

Analysis of Variance↗
PubMed1998

Diadochokinetic skills: normal and atypical performance in children aged 3-5 years.

Although diadochokinetic (DDK) tasks are a popular assessment tool in clinical practice, the interpretation of their results is often limited and obscure. This paper examines the development of DDK skills in normally developing children (age range 3-5 years) for comparison with three case studies of children with specific speech difficulties. The results are presented in terms of accuracy, rate and consistency of response. The normally-developing children increased the accuracy and consistency but not the rate of their responses between the ages of 3 and 5 years. The three case study children (matched on severity of speech difficulty) not only performed differently from control children on some of the measures but also performed differently from each other. The diagnostic value of a developmental DDK profile is discussed.

Child↗
PubMed1996

Developing new synthetic catalysts. How nature does it.

Paleomolecular biochemistry is a new field of science that seeks to understand how life emerged and developed in interaction with its geophysical surroundings. It is an experimental science, involving reconstruction of extinct biomolecules in the laboratory, studying their properties in the laboratory, and inferring details of their behavior and function in the context of geological data. An outline is provided of some tools of this field, together with its application to the study of two specific systems, ribonuclease and alcohol dehydrogenase.

Amino Acid Sequence↗
PubMed1995

Reconstructing the evolutionary history of the artiodactyl ribonuclease superfamily.

The sequences of proteins from ancient organisms can be reconstructed from the sequences of their descendants by a procedure that assumes that the descendant proteins arose from the extinct ancestor by the smallest number of independent evolutionary events ('parsimony'). The reconstructed sequences can then be prepared in the laboratory and studied. Thirteen ancient ribonucleases (RNases) have been reconstructed as intermediates in the evolution of the RNase protein family in artiodactyls (the mammal order that includes pig, camel, deer, sheep and ox). The properties of the reconstructed proteins suggest that parsimony yields plausible ancient sequences. Going back in time, a significant change in behaviour, namely a fivefold increase in catalytic activity against double-stranded RNA, appears in the RNase reconstructed for the founding ancestor of the artiodactyl lineage, which lived about 40 million years ago. This corresponds to the period when ruminant digestion arose in the artiodactyls, suggests that contemporary artiodactyl digestive RNases arose from a non-digestive ancestor, and illustrates how evolutionary reconstructions can help in the understanding of physiological function within a protein family.

Amino Acid Sequence↗
PubMed1993

Psycholinguistic assessment of developmental speech disorders.

Although various psycholinguistic models of speech and language processing have been developed to account for levels of breakdown in developmental speech disorders, it is not obvious how they are to be applied in clinical practice. At the same time, speech and language therapists have routinely been using a wide range of procedures, including published tests, that tap different levels of phonological processing in the child. When analysed and classified appropriately, these procedures can form the basis for a comprehensive psycholinguistic investigation of developmental speech disorders. The aim of this paper is to present a clinically usable, needs-driven but theoretically motivated framework for investigation. The framework is organised in terms of a series of questions that the clinician can pose about the levels of deficit in processing that may be giving rise to the child's speech problems. It is illustrated by means of a case study of a child with a severe developmental speech disorder, which reveals a complex pattern of deficits within the speech processing chain. As the main purpose of the framework is to provide a useful clinical tool to facilitate the planning of appropriate therapy for the individual child, some therapy objectives deriving from the assessment are outlined.

Child, Preschool↗
PubMed1992

Developmental verbal dyspraxia. I: A review and critique.

Developmental verbal dyspraxia is examined from four perspectives: clinical, phonetic, linguistic and cognitive. The paper critically discusses the problems encountered when criteria for identifying acquired speech disorders in the adult population are applied to children's speech difficulties without modifications. It is argued that studies of verbal dyspraxia in children have ignored the unfolding nature of this condition and that a developmental perspective has been lacking in the literature. A need for the inclusion of appropriate control groups and longitudinal case studies is identified. The issue and process of differential diagnosis are addressed and a checklist of criteria for identifying developmental verbal dyspraxia is included. It is noted that this process will inevitably be lengthy with data needed from different aspects of a child's development. Phonetic characteristics alone may not be sufficient to recognise this medical condition with its complex psycholinguistic and educational consequences.

Articulation Disorders↗
PubMed1992

Developmental verbal dyspraxia. II: A developmental perspective on two case studies.

A longitudinal study of the speech errors of two school-age children with what was described as developmental verbal dyspraxia is presented. By comparing them with a group of normally developing children matched on articulation age, it was possible to identify speech errors not typical of earlier speech development, involving problems with syllable structure planning and vocal tract coordination. The speech-disordered children could produce more words correctly than the controls, but, when they did make speech errors, these were more serious than those found in the younger children. The speech-disordered children were followed up 4 years later. Although their speech had improved, they presented with the same profile of error types. They had increased intelligibility by adding more word-specific articulations but still had difficulties with novel and complex material. The adoption of a developmental framework in this study allowed the identification of different levels of breakdown within the speech production process. The case-study method is recommended to investigate how these levels may interact and the clinical implications of the findings are outlined.

Aging↗
PubMed1991

Site-directed mutagenesis of bovine pancreatic ribonuclease: lysine-41 and aspartate-121.

Chemical modification studies suggest that two residues of bovine pancreatic ribonuclease A (RNase A), Lys-41 and Asp-121, are important for catalysis. Three mutants of RNase A have been prepared, two point mutants with Lys-41 altered to Arg-41 and Asp-121 altered to Glu-121, and a double mutant where both residues are altered. The Lys-41 Arg mutant has ca. 2% the catalytic activity (kcat/Km) of the native protein, while the Asp-121Glu mutant has ca. 17% the catalytic activity of the native protein. The double mutant has catalytic activity comparable to the Lys-41Arg mutant.

Amino Acid Sequence↗
PubMed1990

The ribonuclease from an extinct bovid ruminant.

The sequence of the ribonuclease from the ancestor of swamp buffalo, river buffalo, and ox, corresponding approximately to Pachyportax latidens, an extinct ruminant known from the fossil record, has been reconstructed using the rule of 'maximum parsimony'. This protein and two sequences that may have been intermediates in the evolution of modern ribonuclease have been constructed in the laboratory by site-directed mutagenesis, and their properties examined.

Amino Acid Sequence↗
PubMed1987

Expression of bovine pancreatic ribonuclease A in Escherichia coli.

A synthetic gene for bovine pancreatic ribonuclease A (RNase A) has been expressed in Escherichia coli as a fusion protein with beta-galactosidase linked by the tetrapeptide Ile-Glu-Gly-Arg. RNase A was cleaved from the fusion using factor Xa, and the resulting product purified and reconstituted. The isolated RNase A was chromatographically, catalytically, and immunologically identical with authentic RNase A. This work argues that the method suggested by Nagai and Thogersen [Nagai, K. & Thogersen, H. C. (1984) Nature (Lond.) 309, 810-812] for releasing fusion proteins is quite general, even when applied to particularly complicated expression problem. The procedure here makes RNase A available for the first time as a model for studying structure-function relationships in proteins using site-directed mutagenesis.

Animals↗
PubMed1984

Total synthesis and cloning of a gene coding for the ribonuclease S protein.

A gene for ribonuclease S protein, has been chemically synthesized and cloned. The gene is designed to have 25 specific restriction endonuclease sites spaced at short intervals, permitting its structure to be rapidly modified. This flexibility facilitates tests of hypotheses relating the primary structure of the enzyme to its physical and catalytic behavior.

Amino Acid Sequence↗
PubMed1984

Prevalence of hepatitis B markers in the anesthesia staff of a large inner-city hospital.

Thirty-four of seventy anesthesia staff members from an inner-city hospital evidenced past infection with hepatitis B. This is more than twice the prevalence previously reported for university-affiliated hospitals. Our findings suggest that screening before vaccinating is likely to be cost-effective for senior or foreign-born urban health care personnel in high-risk specialties, and vaccinating without screening is likely to be cost-effective for all persons newly entering high-risk specialties, including anesthesiology.

Anesthesia Department, Hospital↗
PubMed1983

Spelling performance of children with developmental verbal dyspraxia.

The ability of four children with developmental verbal dyspraxia to imitate, spell, read and copy regular single-syllable words was investigated. The children were found to have more difficulty in spelling and reading these words than a group of children with normal speech who were matched for reading age. It is suggested that 'dyspraxic' children are subject to a phonetic spelling deficit which arises because of a difficulty in segmenting words at a speech-sound level.

Child↗
PubMed1977

Parenteral nutrition of adults with a 900 milliosmolar solution via peripheral veins.

UNLABELLED: The objective of this study was to compare the nutritional value of three parenteral fluids: a conventional solution (400 milliosmoles/liter, containing Na, K, and Cl in 5% glucose); the concentrated hyperalimentation solution of Dudrick (1,800 milliosmoles/liter, containing Na, K, Cl, Mg, Ca, P, and amino acids in 20% glucose); and an experimental solution (900 millisomoles/liter, containing Na, K, Cl, Mg, Ca, P, and amino acids in 6.5% glucose). These three solutions are termed P400, C1,800, and P900, respectively. Preliminary studies showed that when 5 mg of cortisol/liter were added to P900, this fluid could be infused through peripheral veins for as long a time (average 114 hr) as P400 before local reaction necessitated changing the site. When P400 was infused in undernourished subjects without oral intake, balances of N, P, Mg, and Ca/70 kg of body weight per day were strongly negative (-4 g, -0.4 g, -6 mEq, and -0.2 g, respectively), whereas balances of K were about zero and those of Na and Cl were positive. Weight loss occurred. In the same patients, P900 containing 5 mg of cortisol/liter converted balances of N, P, Mg, and K to positive, and stimulated weight gain. Comparison of P900 (containing cortisol) and C1,800 in three emaciated subjects showed that the latter fluid caused a 2 to 4 times greater degree of positive balance in N, P, K, and Mg than the former. Comparison of P900 (containing cortisol) + 670-1700 cal by mouth with C1,800 in four undernourished subjects showed no statistically significant difference between these two programs. CONCLUSIONS: by adding 5 mg of cortisol/liter to P900, the fluid can be infused through peripheral veins. P900 is intermediate in nutritional value between P400 and C1,800. P900 without oral supplement prevents negative balance of all elements except Ca. P900 + daily oral intake of 670-1700 cal is nutritionally equivalent to C1,800.

Adult↗