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J Andrews

Publications and source records attributed to J Andrews.

At least 163 records · Page 9Linked to original sources
PubMed1994

Effects of substitution of Thr63 by alanine on the structure and function of Lactobacillus casei dihydrofolate reductase.

A mutant of Lactobacillus casei dihydrofolate reductase has been constructed in which Thr63, a residue which interacts with the 2'-phosphate group of the bound coenzyme, is replaced by alanine. This substitution does not affect kcat, but produces an 800-fold increase in the Km for NADPH, which reflects dissociation of NADPH from the enzyme-NADPH-tetrahydrofolate complex, and a 625-fold increase (corresponding to 3.8 kcal/mol) in the dissociation constant for the enzyme-NADPH complex. The difference in magnitude of these effects indicates a small effect of the substitution on the negative cooperativity between NADPH and tetrahydrofolate. Stopped-flow studies of the kinetics of NADPH binding show that the weaker binding arises predominantly from a decrease in the association rate constant. NMR spectroscopy was used to compare the structures of the mutant and wild-type enzymes in solution, in their complexes with methotrexate and with methotrexate and NADPH. This showed that only minimal structural changes result from the mutation; a total of 47 residues were monitored from their resolved 1H resonances, and of these nine in the binary complex and six in the ternary differed in chemical shift between mutant and wild-type enzyme. These affected residues are confined to the immediate vicinity of residue 63. There is a substantial difference in the 31P chemical shift of the 2'-phosphate of the bound coenzyme, reflecting the loss of the interaction with the side chain of Thr63. The only changes in nuclear Overhauser effects (NOEs) observed were decreases in the intensity of NOEs between protons of the adenine ring of the bound coenzyme and the nearby residues Leu62 and Ile102, showing that the substitution of Thr63 does cause a change in the position or orientation of the adenine ring in its binding site.

Alanine↗
PubMed1994

Loss of salt-tolerance and transformation efficiency in Escherichia coli associated with sub-lethal injury by centrifugation.

Sub-lethal injury of Escherichia coli has been detected following centrifugation at g-forces between 5 and 30 kg. The extent of injury was measured either as a reduction in colony forming ability when plated onto NaCl-containing plates (2% w/v), or as a reduction in transformation efficiency associated with plasmid pBR322 encoding ampicillin resistance. In both cases, the extent of sub-lethal injury was found to increase with increasing centrifugal force and probably reflects structural damage to the cell envelope.

Centrifugation↗
PubMed1994

Caregiver role appraisal and caregiver tasks as factors in ending caregiving.

This study focuses on factors related to why people with primary responsibility for providing care to ADL-impaired elderly persons ended their caregiving roles. Data are from the 1982 National Long-Term Care Survey and the Informal Caregiver Survey. Variables reflecting characteristics of care recipients and caregivers, caregiver role responsibilities, and appraisal of the caregiver role are investigated. Of particular interest is the influence of role responsibilities, such as number of ADL tasks, relative to appraisal of the caregiving role. The results indicate that factors other than role responsibilities are important in understanding who ends caregiving, and that risk factor profiles may prove a useful means of targeting caregivers at greatest risk of ending caregiving.

Activities of Daily Living↗
PubMed1994

Sexual transmission of simian T-lymphotropic virus type I: a model of human T-lymphotropic virus type I infection.

Simian T-lymphotropic virus type-I (STLV-I) seronegative females placed together with seropositive males for breeding purposes were followed from 1984-1990 to determined seroconversion rates by enzyme immunoassay and western immunoblot analysis. Two of 26 females and 1 of 4 males previously negative for antibodies to STLV-I seroconverted during the study period. Statistical analysis of sexual encounters indicated that the probability of a seronegative female testing positive for STLV-I after a sexual encounter with a seropositive male is less than 4%. These data indicate that even though sexual contact is important in the transmission of STLV-I, it may not be an efficient mode of viral infection. These data also suggest that female-to-male transmission of STLV-I occurs, as recently reported for human T-lymphotropic virus type-I (HTLV-I) infection. These results are important because HTLV-I and STLV-I share many features in common including routes of viral transmission. In addition, the difficulty of clearly quantitating the risk of sexual transmission in humans makes the primate animal model a valuable alternative to study the human infection.

Animals↗
PubMed1993

Synthesis and relative potencies of new constrained CRF antagonists.

Two series of CRF antagonists with N alpha- and C alpha-methylated alanine and leucines were evaluated for their biological activities in vitro and in vivo in several systems. The poly-N-methylated analogue of alpha-helical-CRF9-41, [N alpha MeLeu10,15,27,37,N alpha MeAla22,32,41]-alpha-Hel-CRF9-41, was found to be considerably less potent than the parent non-N-methylated analogue. This result was expected on the basis that alpha-helicity was thought to be required for biological activity and the prediction that backbone substitutions on the nitrogen have a tendency to break alpha-helices (a hypothesis that was confirmed by circular dichroism). Next, a series of constrained analogues of the potent CRF antagonist, [DPhe12,Nle21,38]h/rCRF12-41, was synthesized that contained C alpha-methylleucine and/or C alpha-methylalanine (Aib) residues at selected positions. Because C alpha-methylation is recognized to increase alpha-helicity, and because there is now strong NMR data suggesting that residues 6-36 assume a well-defined alpha-helix, it was expected that these analogues would be more potent. Although usual solid-phase peptide synthesis procedures were followed, success in coupling the C alpha-methyl amino acids was obtained only with a 1:1 mixture of BOP/HOBt. In vitro potencies of the synthesized compounds were measured in a collagenase-dispersed anterior pituitary cell culture bioassay. Monosubstituted analogues were shown to be twice to one fourth as potent as the parent compound; while the pluri-substituted peptides were slightly less potent. This decrease in potency might be correlated to an unexpected lower helical content of the pluri-substituted compounds (as determined by CD spectroscopy), as it was suggested that the bioactive conformation of the CRF was predominantly alpha-helical. Interestingly, one analogue, [DPhe12,Nle21,38,C alpha-MeLeu37]h/rCRF12-41, was found to be more potent and longer acting than the parent compound in two in vivo assays measuring ACTH release after intravenous administration to adrenalectomized rats and reversal of stress-induced delay in gastric emptying in the rat after intracisternal administration. The molecular basis for this increased duration of action and potency is being investigated.

Adrenalectomy↗
PubMed1993

Reproductive and thyroid effects of low-level polychlorinated biphenyl (Aroclor 1254) exposure.

As little information is available on the adverse effects of polychlorinated biphenyls (PCBs) on the reproductive system of the male rat, the current study was conducted to evaluate the effects of subchronic administration of the PCB mixture Aroclor 1254 on testicular gamete production and endocrine function. The thyroid hormone thyroxine (T4), which is critical for reproduction and development, was also measured because of the well-documented effects of PCBs on this hormone. Weanling (31-day-old) male Fischer rats were administered 0, 0.1, 1, 10, or 25 mg/kg/day Aroclor 1254 by gavage for 5, 10, or 15 weeks and necropsied. The hormones testosterone (T) and thyroxine were measured in the serum, and body weight and weights of the liver, kidney, testes, seminal vesicle plus coagulating gland, cauda epididymides, and pituitary were taken. At 10 and 15 weeks, testicular interstitial fluid (IF) was collected and T concentration in the IF was measured. Sperm motility was measured from a caudal sperm sample and sperm numbers in the testis and cauda epididymis were determined. In addition, tissues were examined microscopically for histopathological alterations. In the high-dose group, body, seminal vesicle, cauda epididymal, and pituitary weights were depressed at 10 and 15 weeks and cauda epididymal sperm numbers were reduced after 15 weeks of dosing. In contrast, testes weights, testicular sperm numbers, sperm motility, and serum and testicular testosterone levels were unaffected, even in the highest dose group (25 mg/kg/day). Aroclor 1254 administration produced histological alterations in the liver and kidney at doses of 1.0 mg/kg/day and above.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Mesonephric remnant hyperplasia of the cervix: a clinicopathologic analysis of 14 cases.

Lesions derived from mesonephric remnants in the uterine cervix are rare. We describe 14 patients with benign, hyperplastic mesonephric remnant lesions. The patients ranged in age from 31 to 81 years (mean, 47). Four were postmenopausal. The lesions were incidental findings in all but 2 of the patients and frequently had been submitted for consultative pathologic opinion. Two patients did, however, present with symptoms (vaginal bleeding) likely attributable to their lesions and 1 of them had a cervical abnormality on clinical examination. Microscopically, the lesions were composed of lobular or diffuse proliferations of small, round mesonephric tubules which were frequently deep within the cervical wall and often extended to the surface of the cervix. Five of the patients had a referring diagnosis of probable or definite cervical adenocarcinoma due to the infiltrative appearance of the lesions. No mesonephric carcinomas were encountered. Hyperplastic lesions of mesonephric remnants are usually benign, incidental findings but may on occasion be associated with clinical symptomatology and are a potential source of diagnostic confusion for the pathologist.

Adult↗
PubMed1993

The penetration of rufloxacin into sites of potential infection in the respiratory tract.

The concentrations of rufloxacin in the bronchial mucosal, pulmonary epithelial lining fluid and alveolar macrophages were determined in specimens obtained at fibreoptic bronchoscopy. A single oral dose of rufloxacin 400 mg was administered and the samples obtained in the following 72 h. The mean peak serum concentration was 3.56 mg/L, yet the agent was concentrated 1.8-fold in bronchial mucosa, 21.6-fold in alveolar macrophages and 7.7-fold in epithelial lining fluid (as measured by AUC ratios).

Anti-Infective Agents↗
PubMed1993

A comparative study of radionuclide venography and contrast venography in the diagnosis of deep venous thrombosis.

BACKGROUND: The value of the radionuclide blood pool venogram in detecting deep venous thrombosis (DVT) has to date been inadequately evaluated. This is despite its lower complication rate than the gold standard of contrast X-ray venography. AIMS: To compare the relative accuracy and inter observer variability of radionuclide blood pool and X-ray contrast venography as well as evaluate previous literature on radionuclide venography. METHODS: Prospective comparison of radionuclide and contrast venography was performed in 39 patients. Sensitivity and specificity of radionuclide venography were compared to contrast venography and confidence intervals were measured using standard error calculations. A meta-analysis of previous studies was also performed. RESULTS: Significant inter observer variation in reports was present in both radionuclide (37%) and contrast (22%) venograms. Using consensus reports sensitivity of radionuclide venography was 87% compared to contrast venography and specificity was 83%. These results are similar to those obtained in previous studies. Furthermore, sensitivity in specificity in the proximal veins were 90% and 92% respectively which were superior to sensitivity and specificity in the distal veins where it was 74% and 90% respectively. CONCLUSION: The radionuclide venogram appears accurate in the proximal veins and in excluding but not diagnosing distal venous thrombosis.

Adult↗
PubMed1993

Social skills in the context of learning disability definitions: a reply to Gresham and Elliott and directions for the future.

In this article we review the evidence on the status of a social skills deficit as a learning disability (LD) by examining social skills deficits in the context of learning disability definitions. For the most part, social skills deficits fall within the terms that are specified in the definitions; that is, when there is evidence of neurological involvement, social skills deficit as a learning disability is consistent with the focus on listening and speaking that is characteristic of most definitions of learning disabilities. We also conclude that the absence of limiting conditions in extant definitions of learning disabilities makes it difficult to exclude any particular skill or type of knowledge from falling within the bounds of the definitions. Furthermore, we argue that the critical issue centers on the reformulation of the definition of learning disabilities. We suggest two directions in future work: First, the term "learning disability" should be limited to intentional learning contexts. Acceptance of this limitation would clarify at least some of the confusion regarding the domain of learning disabilities. Second, learning disability definitions should become more responsive to recent research on the nature of learning.

Brain Damage, Chronic↗