PubMed Health⌕ Search

Biomedical subjects

J W Little

Publications and source records attributed to J W Little.

At least 19 recordsLinked to original sources
PubMed1992

Gene synthesis, bacterial expression, and 1H NMR spectroscopic studies of the rat outer mitochondrial membrane cytochrome b5.

The gene coding for the water-soluble domain of the outer mitochondrial membrane cytochrome b5 (OM cytochrome b5) from rat liver has been synthetized and expressed in Escherichia coli. The DNA sequence was obtained by back-translating the known amino acid sequence [Lederer, F., Ghrir, R., Guiard, B., Cortial, S., & Ito, A. (1983) Eur. J. Biochem. 132, 95-102]. The recombinant OM cytochrome b5 was characterized by UV-visible, EPR, and 1H NMR spectroscopy. The UV-visible and EPR spectra of the OM cytochrome b5 are almost identical to the ones obtained from the overexpressed rat microsomal cytochrome b5 [Bodman, S. B. V., Schyler, M. A., Jollie, D. R., & Sligar, S. G. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 9443-9447]. The one-dimensional 1H NMR spectrum of the OM cytochrome b5 indicates that the rhombic perturbation of the ferric center is essentially identical to that in the microsomal beef, rabbit, chicken, and rat cytochromes b5. Two-dimensional 1H NMR spectroscopy (NOESY) and one-dimensional NOE difference spectroscopy were used to assign the contact-shifted resonances that correspond to each of the two isomers that result from the rotation of the heme around its alpha-gamma-meso axis. The assignment of the resonances allowed the determination of the heme orientation ratio in the OM cytochrome b5, which was found to be 1.0 +/- 0.1. It is noteworthy that the two cytochromes b5 that have similar populations of the two heme isomers (large heme disorder) originate from the rat liver.

Amino Acid Sequence↗
PubMed1992

In vitro analysis of mutant LexA proteins with an increased rate of specific cleavage.

Specific cleavage of LexA repressor plays a crucial role in the SOS response of Escherichia coli. In vivo, cleavage requires an activated form of RecA protein. However, previous work has shown that the mechanism of cleavage is unusual, in that the chemistry of cleavage is probably carried out by residues in the repressor, and not those in RecA; RecA appears to facilitate this reaction, acting as a coprotease. We recently described a new type of lexA mutation, a class termed lexA (IndS) and here called IndS, that confers an increased rate of in vivo cleavage. Here, we have characterized the in vitro cleavage of these IndS mutant proteins, and of several double mutant proteins containing an IndS mutation and one of several mutations, termed Ind-, that decrease the rate of cleavage. We found, first, that the autodigestion reaction for the IndS mutant proteins had a higher maximum rate and a lower apparent pKa than wild-type LexA. Second, the IndS mutations had little or no effect on the rate of RecA-mediated cleavage, measured at low protein concentrations, implying that the value of Kcat/Km was unaffected. Third, the rate of autodigestion for the double-mutant proteins, relative to wild-type, was about that rate predicted from the product of the effects of the two single mutations. Finally, by contrast, these proteins displayed the same rate of RecA-mediated cleavage as did the single Ind- mutant protein. We interpret these data to mean that the IndS mutations mimic to some extent the effect of RecA on cleavage, perhaps by favoring a conformational change in LexA. We present and analyze a model that embodies these conclusions.

Bacterial Proteins↗
PubMed1992

Dimerization of a specific DNA-binding protein on the DNA.

Many specific DNA-binding proteins bind to sites with dyad symmetry, and the bound form of the protein is a dimer. For some proteins, dimers form in solution and bind to DNA. LexA repressor of Escherichia coli has been used to test an alternative binding model in which two monomers bind sequentially. This model predicts that a repressor monomer should bind with high specificity to an isolated operator half-site. Monomer binding to a half-site was observed. A second monomer bound to an intact operator far more tightly than the first monomer; this cooperativity arose from protein-protein contacts.

Bacterial Proteins↗
PubMed1992

AAEM case report #24: electrodiagnosis in posttraumatic syringomyelia.

An adult male with C-7 quadriplegia developed neck pain. Axillary F central latencies were prolonged, and MRI showed a syrinx extending to C-1. After shunting, F latencies normalized. At subsequent follow-up, a rostral syrinx persisted by magnetic resonance imaging (MRI); motor evoked potential (MEP) latencies were prolonged but F latencies were normal. Later, the syrinx was less distended by MRI, MEPs normalized, and strength improved. We discuss the electrophysiologic methods available for diagnosing and monitoring posttraumatic syringomyelia.

Adult↗
PubMed1992

Dental treatment of the liver transplant patient.

On the basis of recent developments, liver transplantation is no longer considered an experimental procedure. The history and current status of human liver transplantation are reviewed. The complications and side effects of the agents used for immunosuppression are presented. The dental treatment of the patient before and after liver transplantation is discussed in detail.

Dental Care↗
PubMed1992

The need for antibiotic prophylaxis of patients with penile implants during invasive dental procedures: a national survey of urologists.

A national survey of urologists was conducted regarding the need for prophylactic antibiotic coverage for patients with penile implants when undergoing invasive dental treatment. A total of 1,756 questionnaires was sent to urologists in the United States and 297 responses were received, for a participation rate of 17%. The low response rate might be partly related to a low level of concern by urologists due to the lack of reported cases of penile implant infections following invasive dental procedures and the lack of the literature calling attention to this possible association. This is supported by the fact that none of the responding urologists had noted any case of infection of the prosthesis following dental treatment. The majority of urologists who responded did not recommend antibiotic prophylaxis for penile implant patients undergoing invasive dental treatment. The majority of urologists who recommended prophylaxis selected a cephalosporin. None of the responding urologists indicated that they were aware of infection developing in any penile implant patients following invasive dental treatment. The dentist is advised to consult with the urologist of patients with penile implants on an individual basis to determine the need for antibiotic prophylaxis.

Anti-Bacterial Agents↗
PubMed1992

Electrophysiologic findings in post-traumatic syringomyelia: implications for clinical management.

Traumatic spinal cord injured (SCI) patients may develop pain, new weakness and/or sensory loss due to an enlarging fluid-filled cyst in the spinal cord. The clinical history and physical exam are nonspecific and insensitive, particularly for diagnosing and monitoring recurrent or progressive post-traumatic syringomyelia (PTS). We compare the sensitivity and specificity of three electrodiagnostic tests, median and ulnar F waves, electromagnetic motor evoked potentials (MEP), and needle electromyography, with respect to syrinx by imaging (MRI or CT scan) and neurologic progression on serial clinical exams. Central motor conduction time (CMCT) calculated from scalp and spine MEP was the most sensitive diagnostic test. F waves were less sensitive and less specific than the CMCT, and did not provide evidence of syrinxes in the mid or upper cervical cord. Positive sharp wave and fibrillation potentials were the least sensitive and least specific. The CMCT is a useful adjunct to imaging studies for diagnosing and monitoring PTS.

Adult↗
PubMed1992

Antibiotic prophylaxis for prevention of bacterial endocarditis and infections of major joint prostheses [corrected].

The current trend in antibiotic prophylaxis for prevention of endocarditis is toward more simple, effective regimens to promote better patient and dentist compliance. All national medical groups are now recommending oral regimens for all at-risk patients, and most of these groups recommend single-dose oral regimens. The Swiss Working Group recommends multiple-dose amoxicillin for high-risk patients. The American Heart Association recommends two-dose oral regimens for all at-risk patients. Clindamycin appears to be the second drug of choice. The many pharmacokinetically different erythromycin preparations and the high rate of intolerance to many of these preparations has led to this change. No national or international medical groups recommended prophylaxis for patients with prosthetic joints. Most reviews conclude that there is little or no scientific evidence to support this use. It is time to stop the practice of prophylaxis for patients with prosthetic joints. The only patients with joint prostheses who should even be considered for prophylaxis are those patients considered at "high" risk.

American Heart Association↗
PubMed1991

Mutant LexA proteins with an increased rate of in vivo cleavage.

LexA repressor of Escherichia coli is inactivated by a specific cleavage reaction that requires activated RecA protein in vivo. This cleavage reaction can proceed in vitro in the presence of activated RecA or as an intramolecular RecA-independent reaction, termed autodigestion, that is stimulated by alkaline pH. Here we describe a set of LexA mutant proteins that undergo a greatly increased rate of specific cleavage in vivo, compared with wild-type LexA. Efficient in vivo cleavage of these mutant proteins also took place without RecA. Several lines of evidence suggest that cleavage occurred via a mechanism similar to autodigestion. These mutations changed Gln-92, which lies near the cleavage site, to tyrosine, phenylalanine, or tryptophan. The latter mutation increased the rate of cleavage approximately 500-fold. These findings imply that the rate of wild-type LexA cleavage has been optimized during evolution to make the SOS system properly responsive to DNA-damaging treatments. Availability of these mutants will aid in the understanding of rate-limiting steps in intramolecular reactions.

Amino Acid Sequence↗
PubMed1991

Mechanism of specific LexA cleavage: autodigestion and the role of RecA coprotease.

Specific LexA cleavage can occur under two different conditions: RecA-mediated cleavage requires an activated form of RecA, while an intramolecular self-cleavage termed autodigestion proceeds spontaneously at high pH and does not involve RecA. The two cleavage reactions are closely related. We postulate that RecA stimulates autodigestion rather than acting as a typical protease, and it is proposed to term this activity 'RecA coprotease' to emphasize this indirect role. The mechanism of autodigestion is similar to that of a serine protease, and RecA appears to act by reducing the pKa of a critical lysine residue LexA. A new class of mutants, termed lexA (IndS), is described; these mutations increase the rate of LexA cleavage.

Amino Acid Sequence↗
PubMed1991

Repression of the E coli recA gene requires at least two LexA protein monomers.

To analyze the DNA binding domain of E coli LexA repressor and to test whether the repressor binds as a dimer to DNA, negative dominant lexA mutations affecting the binding domain have been isolated. A large number of amino acid substitutions between amino acid positions 39 and 46 were introduced using cassette mutagenesis. Mutants defective in DNA binding were identified and then examined for dominance to lexA+. A number of substitutions weakened repressor function partially, whereas other substitutions led to a repressor with no demonstrable activity and a defective dominant phenotype. Since the LexA binding site has dyad symmetry, we infer that this dominance results from interaction of monomers of wild-type LexA protein with mutant monomers and that an oligomeric form of repressor binds to operator. The binding of LexA protein to operator DNA was investigated further using a mutant protein, LexA408, which recognizes a symmetrically altered operator mutant but not wild-type operator. A mixture of mutant LexA408 and LexA+ proteins, but neither individual protein, bound to a hybrid recA operator consisting of mutant and wild-type operator half sites. These results suggest that at least 1 LexA protein monomer interacts with each operator half site. We discuss the role of LexA oligomer formation in binding of LexA to operator DNA.

Bacterial Proteins↗
PubMed1991

Periodontal status of individuals in early stages of human immunodeficiency virus infection.

The purpose of this study was to evaluate the association of periodontal health and human immunodeficiency virus infection among individuals in the early stages of disease who were participating in randomized placebo-controlled clinical trials of zidovudine. Previous reports have described a rapidly progressive periodontitis and atypical gigivitis associated with late stages of infection by the human immunodeficiency virus. A health history was completed by each subject. Baseline oral examinations were completed on 97 asymptomatic patients and nine with AIDS-related complex (ARC) during their regular clinic visit. Follow-up examinations were conducted at 3-month intervals throughout the 48 weeks of the oral study. Evaluations of plaque, calculus, gingival abnormalities, caries, and periodontal disease were conducted. Periodontal measurements included plaque index (PI), gingival index (GI), bleeding index (BI), probing depth (PD), and observation for cratering, necrosis, and tooth mobility on six teeth in each patient. More than half of the subjects had visited their dentist during the previous year and had had an oral prophylaxis; less than 25% of them had had either restorative work or extractions. The mean scores for periodontal indices averaged over the course of the study in asymptomatic and ARC respectively were: PI: 0.9 (SE 0.04) and 0.9 (SE 0.08), 0.818; GI: 1.0 (SE 0.04) and 0.9 (SE 0.07), P = 0.412; BI: 0.6 (SE 0.04) and 0.4 (SE 0.07), P = 0.278; PD: 2.9 (SE 0.05) and 2.6 (SE 0.10), P = 0.140. There was no evidence of cratering, necrosis, or tooth mobility in either group. Few had calculus or dental caries. There were no clinically significant differences detected between ARC versus asymptomatic patients. Dental histories and oral examinations showed that two groups of patients in early stages of HIV-disease were in good periodontal health.

AIDS-Related Complex↗
PubMed1991

Increasing CD8+ T lymphocytes predict subsequent development of intraoral lesions among individuals in the early stages of infection by the human immunodeficiency virus.

Determining the progression of human immunodeficiency virus (HIV) type 1 infection based on cellular and clinical markers has become increasingly important. Although a number of studies have shown a relationship between the presence of certain oral lesions and progression to AIDS, few data exist regarding the association with T lymphocyte counts. In this study, the question of whether intraoral lesions preceded or were the consequences of changes in T lymphocyte counts was examined. A total of 116 HIV-infected patients participating in two randomized double-blind placebo-controlled trials of zidovudine at the University of Minnesota AIDS Clinical Trials Unit (ACTU) were enrolled in a prospective dental study. Patients were examined for the presence of hairy leukoplakia, candidiasis, herpes simplex, herpes zoster, aphthae, atypical gingivitis, HIV-associated periodontitis, and necrotizing ulcerative gingivitis, as well as other oral lesions, every 3 months for a maximum of four examinations over a 1-year period. T lymphocyte counts before and after each patient's oral examination were obtained. No significant differences were found at examination 1 for differences in gender, race, age, education, tobacco smoking status, ethanol consumption habits, duration in ACTU drug protocol, duration in dental study protocol, or mean T lymphocyte counts between individuals with or without oral lesions at any time in the dental study.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol Drinking↗
PubMed1991

Prosthetic implants: risk of infection from transient dental bacteremias.

This paper examines the issue of risk for infection from transient dental bacteremias in patients with implanted prosthetic devices. Guidelines are available to dentists from the American Heart Association concerning patients with prosthetic heart valves, but other national medical organizations have thus far not provided recommendations regarding patients with other prosthetic devices. The author reviews the literature and offers recommendations for the dental management of these patients.

Dental Care↗
PubMed1991

Methyl prednisolone in double-lumen gel-saline submuscular mammary prostheses: a double-blind, prospective, controlled clinical trial.

At the time of immediate breast reconstruction with submuscular implants, 76 consecutive patients (89 breasts) were randomized into two groups. One received a gel-saline, double-lumen implant with 40 cc of saline added to the outer lumen, while the other received the same implant plus 40 cc of saline and 16 mg methyl prednisolone (40 mg%). Patients were followed for a minimum of 3 years. The groups, which were matched for patient age and implant size, were evaluated at 3, 12, 24, and 36 months for capsular contracture, steroid atrophy, and other complications. With completion of the double-blind study, the patients with submuscular gel-saline implants with only saline added had an overall capsular contracture rate of 38 percent at 3 months, 38 percent at 12 months, and 44 percent at 24 and 36 months. Those with methyl prednisolone had an overall capsular contracture rate of 14 percent at 3 months, and this remained unchanged through the end of the study. The rates of all other complications were comparable. Methyl prednisolone in a dose of 16 mg in 40 cc saline (concentration 40 mg%), when used in the outer lumen of a double-lumen gel-saline implant in a submuscular pocket, is both safe and efficacious in reducing the risk of capsular contracture for a minimum of 3 years in patients undergoing immediate breast reconstruction with submuscular mammary implants.

Adult↗
PubMed1991

Immobilization impairs recovery after spinal cord injury.

The effect of immobilization on motor recovery was studied in adult rats after subtotal spinal cord section. Anesthetized rats underwent three-quarter section of the cord, sparing the left lateral funiculus. After surgery, half the rats were placed in immobilization tubes for three to four weeks; the others were allowed free mobility. Hindlimb motor function was graded at various times in the two groups. In contrast to the marked recovery observed in mobile animals, the immobilized rats with similar cord lesions showed no significant motor recovery during the period of immobilization. Immobilized rats without cord lesions showed minimal transient deficits. In conclusion, hindlimb activity appears to be a necessary condition for motor recovery after subtotal spinal cord injury.

Animals↗