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Biomedical subjects

N Benson

Publications and source records attributed to N Benson.

12 recordsLinked to original sources
PubMed1992

Detection of the optical bands of molybdenum(V) in DMSO reductase (Rhodobacter capsulatus) by low-temperature MCD spectroscopy.

Dimethylsulphoxide (DMSO) reductase from R. capsulatus contains a molybdenum-pterin cofactor at its active site. As prepared the molybdenum is in the 6+ oxidation state, devoid of EPR signals. Stepwise reduction generates an EPR signal characteristic of Mo(V) having hyperfine coupling to a single proton and integrating to less than 25% of the total molybdenum. The low temperature MCD spectrum shows oppositely signed bands between approximately 550-700 nm. These bands are assigned as dithiolene-to-Mo(V) charge transitions. A simple theoretical model can satisfactorily account for the bands in the MCD spectrum. No evidence is found for cysteine coordination to Mo(V).

Circular Dichroism↗
PubMed1992

Mutant lambda repressors with increased operator affinities reveal new, specific protein-DNA contacts.

The binding specificities of four mutant lambda cI repressor proteins with increased affinities for operator DNA were examined. Two mutant repressors (Glu34----Lys and Glu83----Lys) have the same specificity of binding as wild-type repressor, whereas two (Gly48----Ser and Gly48----Asn) have new binding specificities. The Gly48----Asn mutant repressor recognizes lambda operators with changes at base pair 3 with a different order of affinity than wild-type repressor, suggesting that the side chain of Asn48 makes additional specific DNA contacts at or near this base pair. When paired with a change that disrupts the specific interaction of the amino-terminal arm of lambda repressor with DNA (Lys4----Gln), one change that increases the affinity of repressor (Gly48----Ser) suppresses the binding defect of the Lys4----Gln repressor, resulting in a double mutant repressor with a new binding specificity different than that of both its parents and of wild type. These results lend strong support to the model of direct recognition of the lambda operator by lambda repressor proposed from the crystal structure of the repressor/operator complex.

Bacteriophage lambda↗
PubMed1991

Effect of methotrexate on cell cycle and DNA synthesis of astrocytes in primary culture: flow cytometric studies.

Relatively pure population of astrocytes in primary culture were examined by flow cytometry at various time intervals after exposure to 1, 10 and 100 microM of methotrexate (MTX). The percentage population of cells in different phases of the cell cycle was determined using propidium iodide (PI) to measure cellular DNA content. DNA synthesis was assessed by measuring the fluorescence intensity of FITC-conjugated antibody to bromodeoxyuridine (BrdUrd). The two parameters were correlated to determine the location of BrdUrd-incorporating cells within the cell cycle. Exposure of astrocytes to MTX caused a consistent increase in number of cells in S-phase which correlated with the increase in BrdUrd incorporation. These studies provide supportive evidence that the astrogliosis seen in MTX encephalopathy may be due to a primary involvement of astrocytes.

Animals↗
PubMed1989

Phage lambda Cro protein and cI repressor use two different patterns of specific protein-DNA interactions to achieve sequence specificity in vivo.

By assaying the binding of wild-type Cro to a set of 40 mutant lambda operators in vivo, we have determined that the 14 outermost base pairs of the 17 base pair, consensus lambda operator are critical for Cro binding. Cro protein recognizes 4 base pairs in a lambda operator half-site in different ways than cI repressor. The sequence determinants of Cro binding at these critical positions in vivo are nearly perfectly consistent with the model proposed by W. F. ANDERSON, D. H. OHLENDORF, Y. TAKEDA and B. W. MATTHEWS and modified by Y. TAKEDA, A. SARAI and V. M. RIVERA for the specific interactions between Cro and its operator, and explain the relative order of affinities of the six natural lambda operators for Cro. Our data call into question the idea that lambda repressor and Cro protein recognize the consensus lambda operator by nearly identical patterns of specific interactions.

Amino Acids↗
PubMed1988

Eating attitudes as related to demographic and personality characteristics: a high school survey.

A survey of 577 high school students was conducted to assess attitudes toward eating and their relationship to demographic and personality characteristics. Students completed a demographic questionnaire, and Eating Attitude Test (EAT-26) and the Basic Personality Inventory (A-BPI). When a cut-off score of 20 on EAT-26 was applied, overall prevalence of disordered eating attitude was found to be 7.5%. Groups scoring in pathological versus normal ranges showed no significant difference in mean age, socioeconomic status or race. The former group reported significantly shorter height and lower body weight. Of the subjects, 6.06% reported weight below the 10th percentile. This subgroup did not vary from those above the 10th percentile on sociodemographic and psychopathological variables, nor in prevalence of abnormal eating attitudes. Analysis of the A-BPI data showed subjects with abnormal eating attitudes had increased psychopathology in several areas, with greater neurotic tendencies, lower self-esteem and higher levels of deviant thinking and behaviour.

Adolescent↗
PubMed1986

General selection for specific DNA-binding activities.

We present a general strategy for the selection of bacterial clones that express DNA-binding activities corresponding to particular DNA recognition sites. The selection uses a "challenge phage" vector, P22 Kn9 arc-amH1605, into which is substituted a synthetic DNA-binding site for a site that controls transcription of the P22 antirepressor (ant) gene. Constitutive synthesis of antirepressor channels a challenge phage into lytic development and efficiently kills an infected host, unless the substituted site is bound by a specific protein; in this case, the challenge phage prefers lysogenic development, and the host survives and acquires an antibiotic-resistance phenotype. Infections with challenge phages carrying the E. coli Lac operator, phage lambda OL1 operator, or synthetic, "idealized" E. coli Trp and Tn10 Tet operators select clones that express each of the corresponding binding activities. The use of challenge phage vectors may be extended to select clones that express eukaryotic DNA-binding activities.

Base Sequence↗
PubMedDate not supplied

Morphologic study of intermediate filaments in rat hepatocytes.

Rat liver perfused with 0.5% Triton X-100 for 15 to 90 min followed by 1% sodium dodecyl sulfate for 30 min were studied by electron microscopy and polyacrylamide gel electrophoresis. After 15 min of perfusion, a rich network of intermediate filaments and microtubules was visualized in the cytoplasm of hepatocytes. Using stereopairs, branching was visualized. Connections of filaments were noted with nuclei, centrioles, microtubules, vesicles, and rough endoplasmic reticulum. The existence of connections supported the concept that intermediate filaments may function to integrate mechanically the cytoplasmic space as postulated by Lazarides.

Animals↗
PubMedDate not supplied

Severe and progressive steatosis and focal necrosis in rat liver induced by continuous intragastric infusion of ethanol and low fat diet.

Blood alcohol levels (BAL) were maintained at high levels (overall mean +/- S.D. achieved in 14 alcoholic rats was 216.0 +/- 120.1 mg%) in male Wistar rats for 15 to 85 days by continuous intragastric infusion of ethanol and nutritionally defined low fat liquid diet. The ethanol intake was progressively increased from 32% of total calories up to 41.4% in order to maintain high BAL. Pair-fed animals received isocaloric glucose solution and the liquid diet. Despite the low level of dietary fat (4.9% of total calories), histopathological evaluation of the liver revealed severe and progressive fatty infiltration in the alcoholic rats. In addition, following 30 days of intoxication, one third of the animals showed focal necrosis with mononuclear cell infiltration in centrilobular areas of the livers. This was correlated with the markedly elevated levels of SGOT and SGPT in these animals. Pair-fed controls showed no abnormality in the morphology of liver or blood chemistry. Chemical quantitation of liver triglycerides confirmed the histological observation, with triglyceride levels of 61.51 +/- 16.45 and 89.61 +/- 5.94 mg per gm at 30 and 85 days, respectively. Most importantly, the degree of steatosis was tightly and significantly correlated with the mean BAL achieved (r = 0.80, p less than 0.001). These data represent the first confirmation of the hypothesis that continuously high BAL correlate with the severity of alcohol-induced liver pathology.

Alanine Transaminase↗