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E T Johnson

Publications and source records attributed to E T Johnson.

17 recordsLinked to original sources
PubMed2003

Effects of ionizable residues on the absorption spectrum and initial electron-transfer kinetics in the photosynthetic reaction center of Rhodobacter sphaeroides.

Effects of ionizable amino acids on spectroscopic properties and electron-transfer kinetics in the photosynthetic reaction center (RC) of Rhodobacter sphaeroides are investigated by site-directed mutations designed to alter the electrostatic environment of the bacteriochlorophyll dimer that serves as the photochemical electron donor (P). Arginine residues at homologous positions in the L and M subunits (L135 and M164) are changed independently: Arg L135 is replaced by Lys, Leu, Glu, and Gln and Arg M164 by Leu and Glu. Asp L155 also is mutated to Asn, Tyr L164 to Phe, and Cys L247 to Lys and Asp. The mutations at L155, L164, and M164 have little effect on the absorption spectrum, whereas those at L135 and L247 shift the long-wavelength absorption band of P to higher energies. Fits to the ground-state absorption and hole-burned spectra indicate that the blue shift and increased width of the absorption band in the L135 mutants are due partly to changes in the distribution of energies for the zero-phonon absorption line and partly to stronger electron-phonon coupling. The initial electron-transfer kinetics are not changed significantly in most of the mutants, but the time constant increases from 3.0 +/- 0.2 in wild-type RCs to 4.7 +/- 0.2 in C(L247)D and 7.0 +/- 0.3 ps in C(L247)K. The effects of the mutations on the solvation free energies of the product of the initial electron-transfer reaction (P(+)) and the charge-transfer states that contribute to the absorption spectrum ( and ) were calculated by using a distance-dependent electrostatic screening factor. The results are qualitatively in accord with the view that electrostatic interactions of the bacteriochlorophylls with ionized residues of the protein are strongly screened and make only minor contributions to the energetics and dynamics of charge separation. However, the slowing of electron transfer in the Cys L247 mutants and the blue shift of the spectrum in some of the Arg L135 and Cys L247 mutants cannot be explained consistently by electrostatic interactions of the mutated residues with P and B(L); we ascribe these effects tentatively to structural changes caused by the mutations.

Amino Acid Substitution↗
PubMed2002

Electrostatic interactions in an integral membrane protein.

The effects of charge-charge interactions on the midpoint reduction potential (E(m)()) of the primary electron donor (P) in the photosynthetic reaction center of Rhodobacter sphaeroides were investigated by introducing mutations of ionizable amino acids at selected sites. The mutations were designed to alter the electrostatic environment of P, a bacteriochlorophyll dimer, without greatly affecting its structure or molecular orbitals. Two arginine residues at homologous positions in the L and M subunits [residues (L135) and (M164)], Asp (L155), Tyr (L164), and Cys (L247) were changed independently. Arginine (L135) was replaced by Lys, Leu, Gln, or Glu; Arg (M164), by Leu or Glu; Asp (L155), by Asn; Tyr (L164), by Phe; and Cys (L247), by Lys or Asp. The R(L135)E/C(L247)K double mutant also was made. The shift in the E(m)() of P/P(+) was measured in each mutant and was compared with the effect predicted by electrostatics calculations using several different computational approaches. A simple distance-dependent dielectric screening factor reproduced the effects remarkably well. By contrast, microscopic methods that considered the reaction field in the protein and solvent but did not include explicit counterions overestimated the changes in the E(m)() considerably. Including counterions for the charged residues reduced the calculated effects of the mutations in molecular dynamics calculations. The results show that electrostatic interactions of P with ionizable amino acid residues are strongly screened, and suggest that counterions make major contributions to this screening. The screening also could reflect penetration of water or other relaxations not taken into account because of incomplete sampling of configurational space.

Amino Acid Substitution↗
PubMed2001

Alteration of a single amino acid changes the substrate specificity of dihydroflavonol 4-reductase.

Many plant species exhibit a reduced range of flower colors due to the lack of an essential gene or to the substrate specificity of a biosynthetic enzyme. Petunia does not produce orange flowers because dihydroflavonol 4-reductase (DFR) from this species, an enzyme involved in anthocyanin biosynthesis, inefficiently reduces dihydrokaempferol, the precursor to orange pelargonidin-type anthocyanins. The substrate specificity of DFR, however, has not been investigated at the molecular level. By analyzing chimeric DFRs of Petunia and Gerbera, we identified a region that determines the substrate specificity of DFR. Furthermore, by changing a single amino acid in this presumed substrate-binding region, we developed a DFR enzyme that preferentially reduces dihydrokaempferol. Our results imply that the substrate specificity of DFR can be altered by minor changes in DFR.

Alcohol Oxidoreductases↗
PubMed2000

Geographic variation in patient surveillance after radical prostatectomy.

BACKGROUND: Prostate cancer is often diagnosed early enough in its clinical course to permit radical prostatectomy to be done with curative intent, yet many patients experience tumor recurrence. Most patients receive postoperative surveillance, but the intensity of testing varies appreciably. We sought to evaluate the influence of geographic location on the variability of surveillance intensity. METHODS: Questionnaires pertaining to postoperative surveillance were mailed to 4467 members of the American Urological Association (AUA). Practice pattern variation was assessed among 24 large metropolitan statistical areas, among nine United States census regions, and by health maintenance organization penetration rate. RESULTS: Of 4467 urologists surveyed, 1416 (32%) responded and 1050 (24%) responses were evaluable. Correlation analysis showed that mean follow-up intensity across modalities surveyed was highly correlated across tumor, node, metastasis (TNM) stages and years postsurgery. We found no significant main effects attributable to metropolitan statistical area, United States (US) census region, or health maintenance organization (HMO) penetration rate for commonly used surveillance modalities: serum prostate-specific antigen (PSA), office visit, and urinalysis. For infrequently used modalities, there were minimal effects on testing intensity of US census region, metropolitan statistical area, and HMO penetration rate. Few two-way and three-way interactions were significant. CONCLUSIONS: The utilization of commonly used surveillance modalities by urologists caring for patients after radical prostatectomy is not affected by metropolitan statistical area, US census region, or HMO penetration rate.

Adult↗
PubMed2000

How tumor stage affects american urologists' surveillance strategies after prostate cancer surgery.

The factors which influence decision-making among urologists are not well understood. We evaluated how tumor stage in patients subjected to potentially curative surgery for carcinoma of the prostate affects the self-reported follow-up strategies employed by practicing United States urologists. Standardized patient profiles and a detailed questionnaire based on these profiles were mailed to 4,467 randomly selected members of the American Urological Association (AUA), comprising 3,205 US and 1,262 non-US urologists. The effect of TNM stage on the surveillance strategies chosen by respondents was analyzed by repeated-measures ANOVA. There were 1, 050 respondents who provided evaluable data of whom 760 were from the US. The three most commonly used surveillance modalities by urologists were office visit, serum PSA level, and urinalysis. Nine of the 11 most commonly requested modalities were ordered significantly (p<0.001) more frequently with increasing TNM stage. This effect persisted through 10 years of follow-up, but the differences across stage were tiny. Fifty-five percent of US respondents do not modify their strategies at all according to the patient's TNM stage. Most American AUA members performing surveillance after potentially curative radical prostatectomy for otherwise healthy patients use the same follow-up strategies irrespective of TNM stage. These data permit the rational design of a randomized clinical trial of two alternate follow-up plans. The two trial arms would employ office visits, blood tests, and urinalyses at different frequencies based on current actual practice patterns; there would be no imaging tests in either arm.

Adult↗
PubMed1999

The age of the urologist affects the postoperative care of prostate carcinoma patients.

BACKGROUND: Strategies utilized by urologists in managing prostate carcinoma patients after radical prostatectomy vary appreciably. The reason for this is unclear. The authors investigated the effect of practitioner age on management strategies. METHODS: From among the total of 12,500 American Urological Association (AUA) members, 4467 were randomly selected to receive a custom-designed survey about their care of prostate carcinoma patients after radical prostatectomy. Respondents were asked to describe their follow-up practices for patients treated with curative intent, their motivations regarding postoperative surveillance, their methods of evaluating a postoperative increase in serum prostate specific antigen (PSA) level, and their choices of treatment for patients with recurrent prostate carcinoma. RESULTS: One thousand fifty responses were analyzed. There was a statistically significant influence of practitioner age on the management of at-risk patients, but it was quite small. The typical workup for an elevated postoperative serum PSA level also varied significantly according to practitioner age; older urologists ordered more serum prostatic acid phosphatase levels and computed tomography scans of the abdomen and pelvis, whereas younger urologists ordered more bone scans. The treatment of recurrent prostate carcinoma did not vary significantly according to urologist age. The opinions of older urologists regarding the survival benefits of postoperative surveillance were considerably different from the opinions of their younger colleagues. CONCLUSIONS: The results of this study suggest that urologist age accounts for some of the variation in the postoperative management of prostate carcinoma patients. Differences in beliefs regarding the benefits of surveillance may be partially responsible for this. Persuasive clinical research will probably be required to increase the uniformity of practice in this important area.

Acid Phosphatase↗
PubMed1999

Current followup strategies after radical prostatectomy: a survey of American Urological Association urologists.

PURPOSE: Followup care of men who have undergone potentially curative surgical treatment for prostate cancer varies widely among clinicians. To determine current practice patterns we mailed a custom designed questionnaire to American and nonAmerican urologists who were American Urological Association (AUA) members. MATERIALS AND METHODS: Surveys were mailed to a random sample of the approximately 12,000 AUA members, comprising 3,205 Americans and 1,262 nonAmericans. Evaluable surveys were returned by 760 American (24%) and 290 nonAmerican (23%) urologists. Our analysis is based on these 1,050 responses. RESULTS: In generally healthy patients after radical prostatectomy for stages T1 to 2NOMO and T3a to cNOMO prostate cancer the most frequently recommended followup diagnostic tests included office visit with digital rectal examination, serum prostate specific antigen (PSA) and urinalysis. Although there is appreciable variation in the frequency of use of these methods, respondents generally recommended office visit with digital rectal examination, serum PSA and urinalysis every 3 months in year 1, every 6 months in years 2 to 5 and annually thereafter. Other tests, such as serum prostatic acid phosphatase, bone scan, and abdominal and pelvic computerized tomography and magnetic resonance imaging, are rarely recommended. CONCLUSIONS: Our survey provides information regarding current followup strategies recommended by AUA urologists after radical prostatectomy for stages T1 to 2NOMO and T3a to cNOMO disease. Office visits and digital rectal examination, urinalysis and PSA measurement are the main tools that urologists currently use. Although optimal strategy remains unknown, these data permit the rational design of clinical trials of alternate followup strategies based on actual current practice to answer this important question.

Adult↗
PubMed1999

Cymbidium hybrida dihydroflavonol 4-reductase does not efficiently reduce dihydrokaempferol to produce orange pelargonidin-type anthocyanins.

Some angiosperms are limited to a range of possible flower colors. This limitation can be due to the lack of an anthocyanin biosynthetic gene or to the substrate specificity of a key anthocyanin biosynthetic enzyme, dihydroflavonol 4-reductase (DFR). Cymbidium hybrida orchid flowers primarily produce cyanidin-type (pink to red) anthocyanins and lack the pelargonidin-type (orange to brick-red) anthocyanins. To investigate the underlying molecular mechanism of this flower color range, we cloned a Cymbidium DFR gene and transformed it into a DFR- petunia line. We found that the Cymbidium DFR did not efficiently reduce dihydrokaempferol (DHK), which is an essential step for pelargonidin production. Phylogenetic analysis of a number of DFR sequences indicate that the inability to catalyze DHK reduction has occurred at least twice during angiosperm evolution. Our results indicate that developing a pelargonidin-type orange flower color in Cymbidium may require the transformation of a DFR gene that can efficiently catalyze DHK reduction.

Alcohol Oxidoreductases↗
PubMed1998

Evaluation and management of men whose radical prostatectomies failed: results of an international survey.

OBJECTIVES: To determine how urologists evaluate and treat men who develop recurrent prostate cancer after radical prostatectomy. METHODS: Surveys were mailed to 4467 American Urological Association members comprising 3205 U.S. and 1262 non-U.S. urologists randomly selected from a total membership of approximately 12,000. One thousand four hundred sixteen were returned and 1050 (760 U.S. and 290 non-U.S.) surveys were evaluable. RESULTS: To evaluate men with an elevated or rising prostate-specific antigen (PSA) level more than 1 year after radical prostatectomy, 98% of respondents use digital rectal examination, 68% use bone scan, 54% use transrectal ultrasound with biopsy, 36% use abdominal or pelvic computed tomography scan, 31% use transrectal ultrasound without biopsy, 25% use prostatic acid phosphatase, 11% use monoclonal antibody scan, and 5% use abdominal or pelvic magnetic resonance imaging. Respondents evaluate men with an elevated or rising PSA within 1 year of radical prostatectomy similarly. To treat documented local recurrence, 81% of respondents recommend radiation therapy, 7% recommend orchiectomy or luteinizing hormone-releasing hormone (LHRH) agonists, 6% recommend observation only, and 5% recommend combined androgen ablation. To treat documented distant recurrence, 50% recommend combined androgen ablation, 42% recommend orchiectomy or LHRH agonists, and 7% recommend observation only. To treat PSA-only recurrence, 54% recommend observation only, 16% recommend combined androgen ablation, 15% recommend orchiectomy or LHRH agonists, and 13% recommend radiation therapy. CONCLUSIONS: The evaluation of men whose radical prostatectomy failed varies among urologists and does not depend on time of recurrence. Radiation therapy is used by most urologists to treat local recurrence. Hormonal manipulation is used by more than 90% of urologists to treat distant recurrence. More than 50% of urologists recommend observation for men with biochemical-only recurrence.

Adult↗
PubMed1985

Accidental falls among geriatric patients: can more be prevented?

The potential for accidental falls among geriatric patients is of mounting concern. Two hundred forty-one accidental falls over a 12-month period at the VA Medical Center were analyzed retrospectively and the literature reviewed in order to highlight factors that have bearing on the incidence and severity of falls. If a patient's potential for falling could be identified through a grading system based on these premonitory features, preventive measures might be more clearly focused where needed to reduce this frequent hazard in our hospital population.

Accident Prevention↗
PubMed1983

The condom catheter: urinary tract infection and other complications.

A retrospective study of 64 geriatric patients on an extended care unit at the VA Medical Center strongly suggested that long-term use of a condom catheter drainage system (CCDS) (mean use, 35 months) was regularly associated with urinary tract infection. Common nosocomial pathogens were found, particularly Proteus-Providencia. The CCDS was also associated with significant penile complications. It is hoped that these hazards can be minimized by careful application and monitoring of the CCDS.

Aged↗
PubMed1983

Nosocomial infection: update.

A preceptor program on nosocomial infection is offered at the Tuskegee VA Medical Center every six months. It is the only program of this type offered by any VA hospital. Enrollees include infection-control officers from regional hospitals who attend lectures and demonstrations covering a broad range of related issues. It is now accepted that such preceptorships, by increasing awareness of the risk factors and understanding of available preventive controls, can reduce the incidence of nosocomial infections.Up to 5 percent of the 40 million patients admitted to US hospitals each year are compromised by an infection acquired during the hospital stay. This leads to 70,000 deaths per year. The urinary tract is the origin of 40 percent of all nosocomial infections, and surgical wounds account for another 25 percent. Pneumonia is the culprit in 15 percent of cases. Primary bacteremias make up only 4 percent of nosocomial infections, but the mortality is 30 to 50 percent.Staphylococci and gram-negative bacilli, especially E coli, are the common organisms found in hospital-acquired infections. Opportunistic pathogens such as Pseudomonas, Serratia, Candida, and a host of others, including Legionella, are found in debilitated patients.

Cross Infection↗
PubMedDate not supplied

Use of solid-phase extraction systems to improve the sensitivity of Artemia bioassays for trichothecene mycotoxins.

Solid-phase extraction was used to preconcentrate trichothecene mycotoxins from rivers and streams in order to develop and improve a rapid and sensitive bioassay using the brine shrimp Artemia salina. For T-2 toxin, HT-2 toxin, and 4,15-diacetoxyscirpenol, LC50 values obtained were 172, 600, and 700 micrograms/L, respectively. The LC50 for 4-deoxynivalenol was 21 mg/L. A more than 5-fold increase in sensitivity was observed when solid-phase extraction (SPE) was used in conjunction with the Artemia bioassay. For T-2 toxin, HT-2 toxin, and 4,15-diacetoxyscirpenol, LC50/SPE values after solid-phase extraction were 21, 83, and 130 micrograms/L. The use of river and stream waters and chlorinated water did not seem to interfere with the bioassay.

Animals↗