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Biomedical subjects

D Rhodes

Publications and source records attributed to D Rhodes.

At least 145 records · Page 8Linked to original sources
PubMed1981

Gas Chromatography-Mass Spectrometry of N- Heptafluorobutyryl Isobutyl Esters of Amino Acids in the Analysis of the Kinetics of [N]H(4) Assimilation in Lemna minor L.

Rapid, sensitive, and selective methods for the determination of the (15)N abundance of amino acids in isotopic tracer experiments with plant tissues are described and discussed. Methodology has been directly tested in an analysis of the kinetics of [(15)N]H(4) (+) assimilation in Lemna minor L. The techniques utilize gas chromatography-mass spectrometry selected ion monitoring of major fragments containing the N moiety of N-heptafluorobutyryl isobutyl esters of amino acids. The ratio of selected ion pairs at the characteristic retention time of each amino acid derivative can be used to calculate (15)N abundance with an accuracy of +/-1 atom% excess (15)N using samples containing as little as 30 picomoles of individual amino acids. Up to 11 individual amino acid derivatives can be selectively monitored in a single chromatogram of 30 minutes. It is suggested that these techniques will be useful in situations where the small quantities of N available for analysis have hitherto hindered the use of (15)N-labeled precursors.

Journal Article↗
PubMed1980

A low resolution structure for the histone core of the nucleosome.

Image reconstruction to 22 A resolution of the histone octamer (H3)2(H4)2(H2A)2(H2B)2 shows it to have a 2-fold axis of symmetry, and the overall shape of the left-handed helical spool on which to wind about two turns of a flat superhelix of DNA in the nucleosome. From this structure and the results of various cross-linking studies, we have deduced the arrangement of the individual histones. We propose that the (H3)2(H4)2 tetramer forms a dislocated disk which defines the central turn of DNA, while the two H2A-H2B dimers lie one on each face, each associated with about one half a turn.

Animals↗
PubMed1980

Helical periodicity of DNA determined by enzyme digestion.

The periodicity of DNA has been determined by binding short, stiff pieces of DNA to a flat surface and using DNase I to probe the accessibility of the phosphodiester bonds. We have found that the distance between successive DNase I cutting sites is 10.6 +/- 0.1 bases for the DNA immobilized on three different surfaces. We identify this value with the number of base pairs per turn of the DNA double helix in solution.

Binding Sites↗
PubMed1979

Nucleosome cores reconstituted from poly (dA-dT) and the octamer of histones.

In this paper we describe a detailed investigation of the reconstitution of nucleosome cores from poly (dA-dT) and the octamer of histones. We also attempted the reconstitution from the copolymers poly dA.poly dT, poly dG.poly dC and poly (dG-dC). The repeat of the reconstituted chromatin fibre is discussed. The micrococcal nuclease released poly (dA-dT) core particle is found to contain a considerably narrower DNA size distribution that of the native random DNA nucleosome core (12). In addition we have succeeded in obtaining small crystals of the poly (dA-dT) nucleosome core. The DNAase I digestion pattern of the poly (dA-dT) containing nucleosome core is presented. The periodicity of DNAase I cutting sites is found to be about 10.5 bases and is similar to that of the native nucleosome core (12, 13).

Animals↗
PubMed1979

Anion exchange and volume regulation during metabolic blockade of renal cortical slices.

1. The development of swelling of rat and guinea-pig renal cortical slices was studied after metabolic blockade (hypoxia plus glycolytic blockade with iodo-acetic acid) and/or exposure to 'isotonic' high potassium, no sodium solution. 2. Swelling was greater after exposure to oxygenated high potassium solution than after metabolic blockade in physiologic Krebs-Henseleit solution. Swelling was reduced after metabolic blockade in high potassium solution compared to incubation in oxygenated high potassium solution. Increasing periods of transient metabolic blockade in Krebs-Henseleit solution progressively blunted swelling when slices were subsequently incubated in oxygenated high potassium solution. 3. Metabolic blockade in Krebs-Henseleit solution resulted in marked reductions in potassium and increases in sodium. Incubation in high potassium solution resulted in marked increases in potassium and similar low levels of sodium regardless of associated interventions. Metabolic blockade in both media resulted in significantly greater increases in renal cortical chloride than in monovalent cations (potassium plus sodium). Incubation in oxygenated high potassium solution was associated with similar increases in renal cortical chloride and total monovalent cations. 4. Renal cortical losses of solids and protein and increases in renal cortical inulin space were greater after metabolic blockade than after incubation under oxygenated conditions regardless of the incubation media. 5. These data support the conclusion that during metabolic blockade there is a significant replacement of larger intracellular anions by extracellular chloride. The loss of osmotically active intracellular anions limits the increase in renal cortical volume during metabolic inhibition and exposure to high potassium solution.

Animals↗
PubMed1978

The nucleoside sequence of tyrosine tRNA from Bacillus stearothermophilus.

The nucleotide sequence of tRNATyr from B. stearothermophilus has been determined: pG-G-A-G-G-G-G-s4U-A-G-C-G-A-A-G-U-Gm-G-C-U-A-A-m1A-C-G-C-G-G-C-G-G-A-C-U-Q-U-A-ms2i6A-A-psi-C-C-G-C-U-C-C-C-U-U-U-G-G-G-U-U-C-G-G-C-G-G-T-psi-C-G-A-A-U-C-C-G-U-C-C-C-C-C-U-C-C-A-C-C-AOH. A combination of classical fingerprinting methods, partial nuclease P1 digestion and two-dimensional homochromatography and a rapid "read off" sequencing gel technique were used to establish the complete nucleotide sequence.

Base Sequence↗
PubMed1978

The influence of acute alterations in coronary blood flow on left ventricular diastolic compliance and wall thickness.

The extent to which alterations in the coronary blood flow influence left ventricular (LV) diastolic compliance and wall thickness was studied in isolated, isovolumic (balloon in LV), blood perfused dog hearts. Studies were performed at a ventricular volume which was associated with an LV systolic pressure of 100 mm Hg and changes in LV diastolic pressure (at this constant volume) were taken as changes in LV diastolic complicance. When coronary perfusion pressure was reduced to zero (5 min of global ischemia), LV diastolic wall thickness fell from 9.9 +/- 0.9 mm to 9.2 +/- 0.7 mm (P less than 0.01) and LV diastolic pressure fell only 1.3 mm Hg (from 5.5 +/- 1.0 mm Hg to 4.2 +/- 1.1 mm Hg P less than 0.01). In contrast to these findings in 'near normal' ventricles, global ischemia in severely injured hearts (with unphysiologically high diastolic pressures) resulted in marked reductions in diastolic pressure. Thus, moment to moment changes in coronary blood flow can result in alterations in the diastolic properties of the LV. However, these are extreme interventions, and in the clinical setting, changes in coronary dynamics are unlikely to cause significant changes in LV diastolic pressure.

Animals↗
PubMed1977

Initial stages of the thermal unfolding of yeast phenylalanine transfer RNA as studied by chemical modification: the effect of magnesium.

The early stages of thermal unfolding of the tertiary structure of yeast tRNAPhe have been followed, in the presence and absence of Mg2+, by measuring changes in the chemical accessibility of the bases uracil and guanine. The reagent used in these studies is 1-cyclohexyl 3-[2-morpholino(4)-ethyl]carbodiimide methotosylate. 32P-labelled tRNA was used so that the points of modification could be examined with ribonuclease digestion and established fingerprinting techniques. Two regions of protection of Mg2+ have been found. One is within the oligonucleotide U8-A-m2G10 and the other is in the vicinity of residue U-59. The tertiary interactions and the D stem are the most readily melted parts of the teritary structure. In the absence of Mg2+ the region of U-59 is the first part of the tertiary structure to become accessible to the reagent. This is closely followed by the opening up of the 'wobble' G-U base pair in the aminoacyl stem. Most of the triple interactions in the augmented D helix are also disrupted early in the melting. The region of intricate interactions between the invariant G-G part of the D loop and the T-psi-C-G loop contains the most stable set of tertitary structure interactions.

Base Sequence↗
PubMed1977

Structure of nucleosome core particles of chromatin.

Cystals have been obtained on nucleosome cores and analysed by X-ray diffraction and electron microscopy. The core is a flat particle of dimensions about 110 X 110 X 57 A, somewhat wedge shaped, and strongly divided into two 'layers', consistent with the DNA being wound into about 1 3/4 turns of a flat superhelix of a pitch about 28 A. The organisation of the DNA can be correlated with the results to enzyme digestion studies. A change in the screw of the DNA double helix on nucleosome formation can be deduced.

Animals↗
PubMed1976

Morphological features of red blood cells in subjects with sickle cell trait: changes during exercise.

Occasional complications and even death in subjects with sickle cell trait have been attributed to severe physical exertion. However, the extent to which sickling actually occurs during exercise has not been reported. This study examined the red blood cell morphological features immediately following near maximal upright graded bicycle exercise in five asymptomatic black subjects with hemoglobin AS. Exercise produced minimal sickling in vivo, which was not proportional to the intensity of exercise. The amount of sickling in vivo was small in comparison to that observed in the presence of severe hypoxia in vitro, never exceeding 0.75%. in seven normal subjects with hemoglobin AA, exercise did not cause changes in red blood cell morphological features. We conclude that exercise may initiate sickling in subjects with sickle cell trait.

Adult↗
PubMed1976

Pseudotumor of adrenal gland.

A sixty-two-year-old male underwent medical evaluation because of hypertension. A suprarenal mass was detected on pyelography and subsequently confirmed by tomography, angiography, sonography, and adrenal venography. In spite of these positive diagnostic studies surgical exploration revealed a normal adrenal gland surrounded by dense fibroadipose tissue which appeared to account for the pseudotumor.

Adrenal Gland Neoplasms↗
PubMed1975

Urologic complications of appendicitis.

Three patients with appendicitis were seen with bladder tumor, hematuria, and pelvic mass with ureteral obstruction, respectively. These cases represent a spectrum of difficult diagnostic problems and illustrate that appendiceal abscess involving the urinary tract may present as urologic disease. Thus, it is important to consider appendicitis in the differential diagnosis.

Adult↗
PubMed1975

Structure of yeast phenylalanine transfer RNA at 2.5 A resolution.

The x-ray analysis of the monoclinic form of yeast tRNAPhe has been taken to a resolution of 2.5 A by the method of isomorphous replacement. The model proposed at 3 A has been confirmed and extended to reveal additional features of the tertiary structure and of the stereochemistry. An extensive hydrogen bonding network is described involving specific interactions between bases and the ribose-phosphate backbone. The structure of a G-U base pair has been solved.

Base Sequence↗