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Biomedical subjects

K Duncan

Publications and source records attributed to K Duncan.

At least 73 records · Page 4Linked to original sources
PubMed1988

The Saccharomyces cerevisiae ARO1 gene. An example of the co-ordinate regulation of five enzymes on a single biosynthetic pathway.

The ARO1 gene of Saccharomyces cerevisiae encodes the arom multifunctional enzyme. Specific inhibitors of amino acid biosynthesis have been used to obtain evidence that expression of a cloned ARO1 gene is regulated in response to amino acid limitation. Northern blot analysis and sequence studies indicate that ARO1 is regulated by the well characterised S. cerevisiae 'general control' mechanism. This provides a very economical means of simultaneously tailoring the synthesis of five shikimate pathway enzymes to the needs of the cell.

Alcohol Oxidoreductases↗
PubMed1988

ATP-dependent inactivation and slow binding inhibition of Salmonella typhimurium D-alanine:D-alanine ligase (ADP) by (aminoalkyl)phosphinate and aminophosphonate analogues of D-alanine.

In Salmonella typhimurium, D-alanine:D-alanine ligase (ADP) (EC 6.3.2.4) is the second enzyme in the three enzyme D-alanine branch pathway of peptidoglycan biosynthesis. The interaction of this enzyme with a possible transition-state analogue, the (aminoalkyl)phosphinate D-3-[(1-aminoethyl)phosphinyl]-2-heptylpropionic acid [Parsons et al. (1987) Abstracts of Papers, 193rd National Meeting of the American Chemical Society, Denver, CO, MEDI 63, American Chemical Society, Washington, DC], has been studied. This compound is a potent active site directed inhibitor and is competitive with D-alanine (Ki = 1.2 microM); it exhibits time-dependent inhibition in the presence of ATP. Kinetic analysis revealed a rapid onset of steady-state inhibition (kon = 1.35 X 10(4) M-1 s-1) followed by slow dissociation of inhibitory complex(es) with a half-life of 8.2 h. The inhibitory complex was shown to consist of E...I...ATP in equilibrium with E...I, Pi, and ADP. Similar time-dependent inhibition was also observed with D-(1-aminoethyl)phosphonic acid (D-Ala-P) (Ki = 0.5 mM; kon = 27 M-1 s-1; t1/2 for regain = 1.73 min) but not with D-(1-aminoethyl)phosphinic acid, which behaved as a simple competitive inhibitor (Ki = 0.4 mM). The mechanism of inhibition is discussed in the light of the precedents of glutamine synthase inhibition by methionine sulfoximine and phosphinothricin.

Alanine↗
PubMed1987

A eukaryotic repressor protein, the qa-1S gene product of Neurospora crassa, is homologous to part of the arom multifunctional enzyme.

Little is known about the proteins involved in the control of gene expression in eukaryotes. Although some of these proteins have been sequenced, their biochemical functions are not well understood and the identification of homologies to proteins of known activities may give useful clues to the functions of these regulatory proteins. We report here that the qa-1S repressor protein of the fungus Neurospora crassa is strongly homologous to the pentafunctional arom enzyme found in many lower eukaryotes. We believe that this is the first known case of a repressor protein that is unequivocally homologous to metabolic enzymes. These findings allow us to propose likely functions for some regions of the qa-1S protein.

Amino Acid Sequence↗
PubMed1987

The pentafunctional arom enzyme of Saccharomyces cerevisiae is a mosaic of monofunctional domains.

The nucleotide sequence of the Saccharomyces cerevisiae ARO1 gene which encodes the arom multifunctional enzyme has been determined. The protein sequence deduced for the pentafunctional arom polypeptide is 1588 amino acids in length and has a calculated Mr of 174555. Functional regions within the polypeptide chain have been identified by comparison with the sequences of the five monofunctional Escherichia coli enzymes whose activities correspond with those of the arom multifunctional enzyme. The observed homologies demonstrate that the arom polypeptide is a mosaic of functional domains and are consistent with the hypothesis that the ARO1 gene evolved by the linking of ancestral E. coli-like genes.

Alcohol Oxidoreductases↗
PubMed1987

Molecular cloning and over-expression of the glyoxylate bypass operon from Escherichia coli ML308.

A recombinant plasmid carrying an 11 kb restriction-endonuclease-ClaI fragment of genomic DNA from Escherichia coli ML308 was constructed. This plasmid complements an aceA mutation. The plasmid encodes the structural genes of the glyoxylate bypass operon, namely malate synthase A (aceB), isocitrate lyase (aceA) and isocitrate dehydrogenase kinase/phosphatase (aceK), as judged by overexpression of enzyme activities and transcription/translation experiments in vitro. Subcloning confirmed that expression of the aceK gene is essential for growth on acetate.

Cloning, Molecular↗
PubMed1987

The efficiency of folding of some proteins is increased by controlled rates of translation in vivo. A hypothesis.

We propose that the way in which some proteins fold is affected by the rates at which regions of their polypeptide chains are translated in vivo. Furthermore, we suggest that their gene sequences have evolved to control the rate of translational elongation such that the synthesis of defined portions of their polypeptide chains is separated temporally. We stress that many proteins are capable of folding efficiently into their native conformations without the help of differential translation rates. For these proteins the amino acid sequence does indeed contain all the information needed for the polypeptide chain to fold correctly (even in vitro, after denaturation). However, other proteins clearly do not fold efficiently into their native conformation in vitro. We argue that the efficiency of folding of these problematic proteins in vivo may be improved by controlled synthesis of the nascent polypeptide.

Codon↗
PubMed1987

Automatic respiratory failure: sleep studies and Leigh's disease (case report).

A 34-year-old woman with a history of chronic nephropathy, kidney transplant rejections, and repeated hemodialysis developed symptoms of automatic respiratory failure during all states of sleep. The neuropathologic examination revealed symmetric brainstem lesions, explaining the sleep-related respiratory failure. Histology affirmed the diagnosis of Leigh's disease.

Adult↗
PubMed1987

Transventricular aortic valvotomy for critical aortic stenosis in infants.

Ten infants with critical aortic stenosis underwent transventricular valvotomy between November 1983 and September 1984. The ages of the patients ranged from 1 to 38 days (mean 21.2 days). Three patients were less than 1 week of age. One had undergone a previous valvotomy performed with inflow occlusion. Most infants were critically ill when admitted to the hospital, six required inotropic and ventilatory support, and two had peritoneal dialysis before the operation. Transventricular valvotomy was performed through a left thoracotomy with Hegar dilators. Postvalvotomy peak-to-peak gradients ranged from 0 to 35 mm Hg. Three patients died at 2, 3, and 6 weeks after operation. A severe degree of endocardial fibroelastosis was present in one patient, and a second patient died of septicemia caused by wound infection, empyema, and a bronchopleural fistula. Severe left ventricular hypertrophy, with moderate fibroelastosis, was found at autopsy in the third patient. Aortic incompetence was not detected postoperatively. One patient required reoperation 7 months after the transventricular valvotomy. Transventricular valvotomy has proved to be a simple and effective technique to relieve aortic stenosis in sick infants. It permits the correction of associated coarctation of the aorta and avoids a median sternotomy. Results are comparable with the results obtained with either cardiopulmonary bypass or inflow occlusion as seen in both our experience and in the experience of others.

Aortic Valve↗
PubMed1987

Expandable intramedullary device for treatment of fractures in the hand.

Because the hand tolerates disuse so poorly, the beginning of early motion following fractures is important in achieving early restoration of function. This report concerns the use of a unique, expandable intramedullary device for internal fixation of metacarpal or phalangeal shaft fractures that renders enough intrinsic stability that motion may be started early without fear of loss of reduction. The device is applicable for transverse or short oblique fractures and consists of a cylindrical apparatus made of titanium that allows for collapse in the circumferential diameter. It is introduced into the medullary canal in its collapsed state, and then is released to allow reexpansion into its normal diameter in the canal with the fracture reduced over it. This gives excellent fixation and affords stability approaching that of normal bone. Minimal postoperative immobilization is needed and early restoration of motion is possible. The device may also be used to immobilize metacarpal bones or phalanges following osteotomies, and it appears to be excellent for fixation of the bone in digits to be replanted. No complications have occurred in the reported series.

Finger Injuries↗
PubMed1986

The overexpression and complete amino acid sequence of Escherichia coli 3-dehydroquinase.

The enzyme 3-dehydroquinase was purified in milligram quantities from an overproducing strain of Escherichia coli. The amino acid sequence was deduced from the nucleotide sequence of the aroD gene and confirmed by determining the amino acid composition of the overproduced enzyme and its N-terminal amino acid sequence. The complete polypeptide chain consists of 240 amino acid residues and has a calculated subunit Mr of 26,377. Transcript mapping revealed that aroD is a typical monocistronic gene.

Amino Acid Sequence↗
PubMed1986

The serC-aro A operon of Escherichia coli. A mixed function operon encoding enzymes from two different amino acid biosynthetic pathways.

Sub-cloning experiments aimed at precisely locating the E. coli aroA gene, which encodes the shikimate pathway enzyme 5-enolpyruvylshikimate 3-phosphate synthase, showed that in certain constructions, which remain capable of complementing an auxotrophic aroA mutation, expression of aroA is reduced. DNA sequence analysis revealed that a sequence approx. 1200 base pairs (bp) upstream of aroA is necessary for its expression. An open reading frame was identified in this region which encodes a protein of 362 amino acids with a calculated Mr of 39,834 and which ends 70 bp before the start of the aroA coding sequence. This gene has been identified as serC, the structural gene for 3-phosphoserine aminotransferase, an enzyme of the serine biosynthetic pathway. Both genes are expressed as a polycistronic message which is transcribed from a promotor located 58 bp upstream of serC. Evidence is presented which confirms that the aroA and serC genes constitute an operon which has the novel feature of encoding enzymes from two different amino acid biosynthetic pathways.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed1984

The purification of 5-enolpyruvylshikimate 3-phosphate synthase from an overproducing strain of Escherichia coli.

The Escherichia coli aroA gene which codes for the enzyme 5-enolpyruvylshikimate 3-phosphate synthase (EPSP synthase) has been cloned from the lambda-transducing bacteriophage lambda pserC. The gene has been located on a 4.7 kilobase pair PstI DNA fragment which has been inserted into the multiple copy plasmid pAT153. E. coli cells transformed with this recombinant plasmid overproduce EPSP synthase 100-fold. A simple method for the purification of homogeneous enzyme in milligram quantities has been devised. The resulting enzyme is indistinguishable from enzyme isolated from untransformed E. coli.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed1983

Separate motion aftereffects from each eye and from both eyes.

UNLABELLED: Monocular and binocular motion aftereffects (MAEs) are described, which were contingent upon which eye(s) was (were) exposed to the adapting motion. Subjects viewed clockwise rotation of a patterned disc with their left eye, alternating every 5 sec with anticlockwise rotation seen with their right eye, for a 10-min adapting period. RESULT: they saw an anticlockwise motion aftereffect with their left eye, and a clockwise MAE with their right eye. These monocular MAEs lasted for only 2-20 sec, but could be elicited repeatedly over a 2-6 min period, and could still be re-elicited two hours later. In a second experiment, subjects adapted for 10 min to the following cycle of 5-sec rotations: left eye, clockwise: right eye, clockwise: and both eyes together, anticlockwise. RESULT: they saw an anticlockwise MAE with their left eye only or with their right eye only, and a clockwise MAE when both eyes were open. A model of monocular and binocular inputs to motion sensitive neural channels is proposed.

Adaptation, Ocular↗