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Biomedical subjects

D Stone

Publications and source records attributed to D Stone.

At least 145 records · Page 8Linked to original sources
PubMed1980

Absence of arsenite mutagenicity in E coli and Chinese hamster cells.

Because exposure to compounds of arsenic has been implicated as a cause of cancer, an investigation of the mutagenicity of sodium aresenite in E coli and in Chinese hamster cells was performed. In the E coli system, Trp + revertants were not induced by arsenite in a variety of experimental protocols including spot tests, treat and plate protocols, and fluctuation tests. The mutator effect of a tif-1 strain was partially blocked by arsenite. Arsenite did not cause the induction of lambda prophage. In Chinese hamster cells, arsenite did not induce ouabain-resistant mutants or thioguanine-resistant mutants. We conclude that arsenite is not mutagenic to E coli or to Chinese hamster cells. When added to the plating medium, arsenite can act as an anti-mutagen by inhibition of induction of the error-prone SOS repair system in E coli.

Animals↗
PubMed1980

Assessment of function of contractile segments in patients with left ventricular aneurysms by quantitative first pass radionuclide ventriculography. Haemodynamic correlation at rest and exercise.

Thirteen patients with left ventricular aneurysms complicating myocardial infarction were studied by contrast angiography and by first pass radionuclide ventriculography. The ejection fraction of the contractile segment (EFCS) was measured from both studies using a double hemishperoid model, and the values correlated closely. There was a monotonic relation between EFCS and stroke volume index measured from thermodilution cardiac outputs carried out simultaneously with the radionuclide study. When radionuclide ventriculography was performed at submaximal supine exercise, changes in EFCS paralleled changes in the total left ventricular ejection fraction in 10 of the 13 cases. In nine patients, changes in EFCS paralleled changes in stroke volume index and the relation between EFCS and stroke volume index was maintained at exercise. After administration of the vasodilator isosorbide dinitrate to 12 patients, repeat exercise radionuclide ventriculography showed an improvement in left ventricular ejection fraction and in eight patients EFCS improved. First pass radionuclide ventriculography can accurately estimate EFCS, which may be an important factor in predicting the likely response to aneurysmectomy. Changes in EFCS on exercise are reflected in changes in total left ventricular ejection fraction and stroke volume index. Isosorbide dinitrate may improve contractile segment function on exercise.

Adult↗
PubMed1980

Dual isotope stress testing in congenital atresia of left coronary ostium. Applications before and after surgical treatment.

A 38-year-old women presented with an 11-year history of angina pectoris. Coronary arteriography disclosed a large right coronary artery which filled the entire left coronary tree retrogradely. The left main coronary artery ended blindly and was not connected to the aortic root. There were no atherosclerotic lesions in any vessel. Exercise thallium-20l scintigrams showed a perfusion defect in the anterior region of the left ventricle and exercise first pass radionuclide ventriculography showed anterior hypokinesis of the left ventricle with an ejection fraction of 54 per cent, compared with 60 per cent at rest. An aortocoronary saphenous vein graft was constructed to the left coronary artery. Four months after operation the patient is free from symptoms. Repeat thallium scintigrams were normal. Exercise radionuclide ventriculography after operation disclosed no wall motion abnormality, and ejection fraction on exercise was 70 per cent. The mechanism of angina in this patient is unclear but may have been related to the abnormal timing of delivery of blood to the left ventricular myocardium. Dual radionuclide stress testing showed abnormalities after operation. This non-invasive approach may be useful in the assessment of the physiological significance of coronary anomalies and of the value of corrective surgery.

Adult↗
PubMed1979

Porcine liver dihydrofolate reductase. Purification, properties, and amino acid sequence.

Porcine liver dihydrofolate reductase has been purified 18,000-fold to homogeneity. The properties of the purified enzyme were compared to those of dihydrofolate reductase from L1210 cells, the only mammalian reductase for which complete amino acid sequence data are available. The enzymes are very similar when compared on the basis of mechanism and kinetic constants, molecular weights, isoelectric points, and stimulation by salt. A comparison of the amino acid sequences of both enzymes shows an overall identity of 89%. Thus, the similarities seen in inhibitor-binding profiles of mammalian enzymes reflect the close relationship of these enzymes at the molecular level.

Amino Acid Sequence↗
PubMed1979

The amino acid sequence of the trimethoprim-resistant dihydrofolate reductase specified in Escherichia coli by R-plasmid R67.

The amino acid sequence of a trimethoprim-resistant dihydrofolate reductase (EC 1.5.1.3) specified by the R-plasmid R67 is described. The sequence was deduced from automatic and manual sequence analysis of the intact protein, the fragments produced by cyanogen bromide cleavage, and peptides derived from the largest cyanogen bromide fragment by digestion with trypsin, Staphylococcus aureus V8 proteus, chymotrypsin, and Lysobacter enzymogenes alpha-lytic protease. The complete sequence comprises 78 residues in a single polypeptide chain of molecular weight 8444. No evidence of heterogeneity was obtained, indicating that all subunits of the native enzyme are identical. Comparison of the sequence with that of all known dihydrofolate reductases shows no significant sequence homology.

Amino Acid Sequence↗
PubMed1979

R plasmid dihydrofolate reductase with subunit structure.

Dihydrofolate reductase, specified by the type II plasmid of a trimethoprim-resistant Escherichia coli, was purified 40-fold to homogeneity using a combination of gel filtration, DEAE-Sephacel chromatography, and hydrophobic chromatography. The final product shows a single protein band on polyacrylamide gel electrophoresis and has a specific activity of 1.0 unit/mg. The molecular weight of the purified enzyme is 36,000 as determined both by gel filtration and Ferguson analysis of polyacrylamide gel electrophoresis. In contrast, a single polypeptide with a molecular weight of 8,500 was observed on sodium dodecyl sulfate-gel electrophoresis. These experiments suggest that, unlike any bacteria or vertebrate dihydrofolate reductase previously examined, the type II R plasmid reductase is a tetramer composed of four identical subunits. A partial amino acid sequence determination shows no heterogeneity of the subunits and also no clear homology with any reductase sequence previously reported.

Amino Acid Sequence↗
PubMed1979

Evolutionary change in the insulin receptors of hystricomorph rodents.

INSULIN receptors have been thought to have remained unaltered despite evolutionary changes in the hormone(1). Because insulins from hystricomorph rodents are known to be highly substituted compared with other mammalian insulins, we decided to investigate the insulin receptor of some hystricomorphs to determine whether evolutionary change had occurred within the receptor itself. Here we present the first evidence that hystricomorph rodent insulin receptors have undergone evolutionary change.

Journal Article↗
PubMed1979

The amino acid sequence of dihydrofolate reductase from the mouse lymphoma L1210.

The determination of the amino acid sequence of the dihydrofolate reductase (EC 1.5.1.3) from cells of the mouse lymphoma L1210 is described. The protein was cleaved by cyanogen bromide to produce the six fragments CB1 (residues 1 to 14), CB2 (residues 15 to 52), CB3 (residues 53 to 111), CB4 (residues 115 to 125), CB5 (residues 126 to 139), and CB6 (residues 140 to 186). One of the fragments, CB2, contained an internal homoserine derived from a methionine which was not cleaved by cyanogen bromide. The amino acid sequences and order of the cyanogen bromide fragments were determined by a combination of automatic and manual sequence analyses of the fragments and small peptides from tryptic, thermolytic, and Staphylococcus aureus protease digestions. The complete sequence comprises 186 residues in a single polypeptide chain of molecular weight 21,458. Comparison of the sequence of the L1210 dihydrofolate reductase with the sequences of the enzymes from Streptococcus faecium, escherichia coli RT500, and Lactobacillus casei indicates that all enzymes show some homology, which is strongest in the regions forming the substrate binding cleft.

Amino Acid Sequence↗
PubMed1978

The amino acid sequence of rabbit skeletal alpha-tropomyosin. The NH2-terminal half and complete sequence.

The amino acid sequence of the large cyanogen bromide fragment (residues 11 to 127) derived from the NH2-terminal half of alpha-tropomyosin has been determined. This was achieved by automatic sequence analysis of the whole fragment as well as manual sequencing of fragments derived from tryptic digestion of the maleylated fragment and thermolytic, Myxobacter 495 alpha-lytic and Staphylococcus aureus protease digestion of the unmodified fragment. Methionine-containing overlap peptides have been isolated from tryptic digests of the maleylated protein as well as from S. aureus protease digests of the unmodified protein. Coupled with previously published information on the small cyanogen bromide fragments and methionine sequences of tropomyosin, these analyses have permitted the completion of the primary structure of the protein. The complete sequence differs by only 1 residue (Gln-24 instead of Glu-24) from that previously reported. Analysis of the sequence by several authors has permitted rational explanations for the stabilization of its coiled-coil structure, for the existence of its two chains in a nonstaggered arrangement, for a head-to-tail overlap of molecular ends of 8 to 9 residues, for the existence of 14 actin-binding sites on each tropomyosin molecule, and a suggestion for the site of binding of troponin-T.

Amino Acid Sequence↗
PubMed1978

Suicide potential and behavior in children ages 4 to 12.

From a population of 662 children 12 years of age and under, seen at the UCLA Neuropsychiatric Institute, during the years 1970 to 1974, 34 severely depressed children were identified who were also self-abusive and/or suicidal. Case study revealed fragmented, pathological homes, where the children's affect disorders and behaviors were symptomatic of acute family breakdown, marital disharmony, and observed and experienced violence, both verbal and physical. Follow-up on all available children, at least three years posttreatment, revealed that no child had committed suicide. Treatment evaluation by the parents was highly positive, with the great majority of children showing fair to good recovery and adjustment.

Behavior Therapy↗
PubMed1977

The amino-acid sequence of the dihydrofolate reductase of a trimethoprim-resistant strain of Escherichia coli.

The determination of the amino acid sequence of the dihydrofolate reductase from Escherichia coli RT500 is described. The sequence, comprising 159 residues, has been derived from automatic sequencing of the intact protein in conjunction with manual sequencing of lysine-blocked tryptic peptides, Staphylococcus aureus protease peptides, and alpha-lytic protease peptides. Comparison of the sequence with that of the dihydrofolate reductase from a methotrexate-resistant strain of E. coli (MB1428) shows that 145 of the residues are identical. The distribution of the differences along the length of the molecule is discussed.

Amino Acid Sequence↗