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Biomedical subjects

B A Harris

Publications and source records attributed to B A Harris.

At least 37 records · Page 2Linked to original sources
PubMed1995

The structure of unliganded reverse transcriptase from the human immunodeficiency virus type 1.

The crystal structure of the reverse transcriptase (RT) from the type 1 human immunodeficiency virus has been determined at 3.2-A resolution. Comparison with complexes between RT and the polymerase inhibitor Nevirapine [Kohlstaedt, L.A., Wang, J., Friedman, J.M., Rice, P.A. & Steitz, T.A. (1992) Science 256, 1783-1790] and between RT and an oligonucleotide [Jacobo-Molina, A., Ding, J., Nanni, R., Clark, A. D., Lu, X., Tantillo, C., Williams, R. L., Kamer, G., Ferris, A. L., Clark, P., Hizi, A., Hughes, S. H. & Arnold, E. (1993) Proc. Natl. Acad. Sci. USA 90, 6320-6324] reveals changes associated with ligand binding. The enzyme is a heterodimer (p66/p51), with domains labeled "fingers," "thumb," "palm," and "connection" in both subunits, and a ribonuclease H domain in the larger subunit only. The most striking difference between RT and both complex structures is the change in orientation of the p66 thumb (approximately 33 degrees rotation). Smaller shifts relative to the core of the molecule were also found in other domains, including the p66 fingers and palm, which contain the polymerase active site. Within the polymerase catalytic region itself, there are no rearrangements between RT and the RT/DNA complex. In RT/Nevirapine, the drug binds in the p66 palm near the polymerase active site, a region that is well-packed hydrophobic core in the unliganded enzyme. Room for the drug is provided by movement of a small beta-sheet within the palm domain of the Nevirapine complex. The rearrangement within the palm and thumb, as well as domain shifts relative to the enzyme core, may prevent correct placement of the oligonucleotide substrate when the drug is bound.

Binding Sites↗
PubMed1994

Activation of Gi protein by peptide structures of the muscarinic M2 receptor second intracellular loop.

The muscarinic M2 receptor that normally couples via Gi to inhibit adenylyl cyclase was made to couple to Gs by exchange of its third intracellular loop for the comparable domain of the beta 2-adrenoceptor. In HeLa cells transfected with the recombinant M2 beta i-3 cDNA, the chimaeric receptor showed carbachol-mediated activation of adenylyl cyclase (EC50 = 73 nM) that was blocked by atropine, but not by propranolol. The chimaeric receptor was shown to mediate a carbachol-stimulated, Bordetella pertussis toxin-sensitive GTPase activity in membranes of transfected HeLa cells. Interestingly, stimulation of adenylyl cyclase by carbachol was 2-fold higher in transfected cells that had been pretreated with pertussis toxin. These data suggested that the M2 beta i-3 receptor was able to couple to both Gi and Gs, and that the ability to recognise and stimulate Gi did not involve the third cytoplasmic loop of M2. We investigated peptide elements taken from the second intracellular loop of the M2 receptor for their ability to mediate activation of Gi and found that a nine amino acid peptide representing the C-terminal sequence, VKRTTKMAG-NH2 (V9G), was capable of inhibiting forskolin-stimulated adenylyl cyclase by up to 18% and could stimulate high affinity GTPase activity of rat brain membranes by 32%. Further, V9G was shown to cause a doubling of the initial rate of [35S]GTP gamma S binding to purified bovine brain Gi/Go in reconstituted phospholipid vesicles. These data identify a domain on the second intracellular loop of the muscarinic M2 receptor that is involved in the selection of a pertussis toxin-sensitive G protein.

Adenylate Cyclase Toxin↗
PubMed1994

Fitting the treatment to the problem: deciding where to refer substance abusers.

The average physician sees a broad spectrum of substance-abusing patients whose illness levels may range from mild to severe. Considering the number and nature of substance abuse treatment options available, choosing the most appropriate treatment for any given patient may be confusing. This article provides workable guidelines for physicians based on a patient placement manual developed by the American Society of Addiction Medicine.

Alcoholism↗
PubMed1994

A strength training program for postmenopausal women: a pilot study.

This pilot study examined a specific exercise program designed for skeletal muscle strengthening in postmenopausal women. The program consisted of patterns of movement using diagonal and spiral patterns, superimposed on a progressive weight-bearing sequence from prone lying to standing. Progressive resistance was provided with the use of progressively thicker elastic straps. Eighteen of an initial 22 healthy volunteer women aged 50 to 64 years completed 8 weekly hour-long group exercise sessions supplemented with twice weekly sessions at home to pilot test the program's safety, acceptability, and effectiveness in changing muscle strength. A physical therapist conducted baseline and final quadriceps, hamstrings, and grip strength assessments using a portable isokinetic dynamometer. Participants achieved a 21% increase in quadriceps (p < or = .001), 9% increase in hamstrings (p < or = .07), and a 14% increase in grip strength (p < or = .002). A positive dose-response relationship was observed between strength gains and compliance with the program. This approach to strength training in postmenopausal women is feasible and effective in increasing muscle strength. It has considerable promise and deserves further testing and evaluation.

Biomechanical Phenomena↗
PubMed1993

Reliability of eccentric isokinetic knee flexion and extension measurements.

This study assessed the test-retest reliability of knee isokinetic eccentric muscle performance in subjects with and without a history of tibio-femoral pathology. Nineteen adults were tested at 60 degrees/sec and 180 degrees/sec on three occasions using a standardized protocol that incorporates a same-session learning phase. Results revealed moderate to excellent reliability for average peak torque test-retest ICC (2,1) = .58 to .96, total work ICC = .63 to .93, and power ICC = .67 to .93. Joint angle at peak torque was unreliable (ICC = .01 to .69) for both muscle groups at both angular velocities. Knee flexion reliability was higher than extension reliability at both 60 degrees/sec and 180 degrees/sec. Subjects with tibio-femoral pathologies had ICC values lower than the healthy subjects. Reliable eccentric isokinetic measurements can be obtained for average peak torque, total work, and power. Clinicians should not assume the same degree of reliability in testing patients as in testing healthy subjects.

Adult↗
PubMed1993

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Fetus↗
PubMed1993

Reliability of dynamic and isometric testing of shoulder external and internal rotators.

Advances in isokinetic technology allow the physical therapist to assess concentric, eccentric, and isometric muscle performance at the shoulder in various positions. Research is limited, however, on the reliability of isokinetic measurements. The purposes of this study were: 1) to determine the test-retest reliability of concentric, eccentric, and isometric muscle performance measurements of shoulder external and internal rotation in the scapular plane test position and 2) to compare this reliability between the involved and uninvolved limb of subjects with a history of unilateral shoulder pathology. Fourteen males and 10 females (17-58 years) were tested on two occasions at 1-week intervals with the Biodex isokinetic dynamometer. Peak torque, total work, and average power were recorded for concentric tests at angular velocities of 60 and 120 degrees/sec and for eccentric tests at 60 degrees/sec. Maximum average isometric torque was recorded in two positions. Means, standard deviations, and mean differences between sessions with 95% confidence intervals were calculated. Intraclass correlation coefficients (ICCs) were used to determine test-retest reliability. Isometric tests were generally most reliable (ICC = .81-.93), followed by concentric (ICC = .60-.95) and eccentric tests (ICC = .44-.92). Isokinetic and isometric reliability were usually higher for involved than uninvolved shoulders. The implication of these findings is that there appears to be greater variability with eccentric than concentric or isometric testing of shoulder rotation. Factors that possibly contributed to variability are discussed. Clinicians should recognize potential sources of testing error when obtaining isokinetic measurements for use in clinical decision-making. Further refinement of isokinetic testing protocols at the shoulder is recommended.

Adolescent↗
PubMed1992

Isolation of the leucine aminopeptidase gene from Aeromonas proteolytica. Evidence for an enzyme precursor.

The leucine aminopeptidase of Aeromonas proteolytica (EC 3.4.11.10) is a monomeric metalloenzyme having the capacity to bind two Zn2+ atoms in the active site. Structural information of this relatively small aminopeptidase that could illuminate the catalytic mechanism of the metal ions is lacking; hence, we have obtained sequences from the purified enzyme, cloned the corresponding gene, and expressed the recombinant protein in Escherichia coli. The deduced primary amino acid sequence of this secreted protease suggests a potential signal peptide at the NH2 terminus. Expression of the recombinant and native proteins in E. coli and in extracts of culture media of A. proteolytica indicates that the aminopeptidase is secreted as an active and thermosensitive 43-kDa protein that is rapidly transformed to thermostable forms of 30 and 32 kDa. Comparison of the deduced amino acid sequence of the A. proteolytica leucine aminopeptidase with other Zn(2+)-binding metalloenzymes failed to show homologies to the consensus binding sequence His-Glu-X-X-His for the metal ion.

Aeromonas↗
PubMed1991

A randomized, double-blind trial of prostaglandin E2 gel for cervical ripening and meta-analysis.

The ability of prostaglandin E2 to prepare the unripe cervix before an indicated labor induction is controversial. We therefore tested 100 pregnant women in a randomized, double-blind trial with intracervical prostaglandin E2 gel, 0.5 mg. The 53 women who received the placebo gel had an outcome similar to that of the 47 women who received the prostaglandin E2 gel. The mean change in cervical score, mean application-to-delivery interval, incidence of uncomplicated spontaneous labor, incidence of cesarean delivery for a failed induction, and the overall cesarean section rate were not significantly different for the two groups. A meta-analysis, incorporating 18 studies of 1811 patients who received a single application of at least 5 mg prostaglandin E2 gel intravaginally or 0.5 mg intracervically, demonstrated no significant decrease in the overall cesarean delivery rate (p = 0.85). We conclude that the use of single-dose intracervical prostaglandin E2 gel for cervical ripening has little effect on labor induction. Moreover, the use of single-dose intracervical or intravaginal prostaglandin E2 gel does not alter the incidence of cesarean delivery, even when large numbers of patients are analyzed by combining the results of similar reports.

Adult↗
PubMed1991

The flavivirus envelope protein E: isolation of a soluble form from tick-borne encephalitis virus and its crystallization.

By the use of limited trypsin digestion of purified virions, we generated a membrane anchor-free and crystallizable form of the tick-borne encephalitis virus envelope glycoprotein E. It retained its reactivity with a panel of monoclonal antibodies, and only subtle structural differences from the native protein E were recognized. Treatment with the bifunctional cross-linker dimethylsuberimidate resulted in the formation of a dimer. Crystallization experiments yielded hexagonal rod-shaped crystals suitable for X-ray diffraction analysis.

Amino Acid Sequence↗
PubMed1991

A comparison between computer-controlled and set work rate exercise based on target heart rate.

Good exercise prescriptions provide work rates (WRs) that maintain heart rates (HR) in a target zone and at a percent of maximum metabolic equivalent (%METmax). HR and MET were evaluated from computer-controlled and set WR (constant speed) sessions (20 min at 65% METmax). Computer-controlled WR used a control algorithm to adjust speed and grade to maintain the target HR. The set WR (mean +/- S.D.) HR (139 +/- 8 bpm) was lower (p less than 0.05) than the target (147 +/- 3 bpm) and computer-controlled HRs (153 +/- 5 bpm). The set WR MET (8.6 +/- 2.2) was not different than the target (8.6 +/- 2.2), but both were lower than computer-controlled exercise (9.7 +/- 2.2). Computer-control time in target HR zone (16 +/- 5 min) was significantly (p less than 0.004) greater than set WR exercise (6 +/- 5 min). Computer-controlled WR was significantly better in maintaining target HR and the MET values were not physiologically different than target WRs.

Adult↗
PubMed1989

HIV-1 protease: mutagenesis of asparagine 88 indicates a domain required for dimer formation.

Considerable interest exists in the HIV-1 protease for biochemical studies as a potential therapeutic target of acquired immunodeficiency syndrome. We have produced the retroviral enzyme in E. coli from a synthetic gene encoding the protease that was constructed by assembling six overlapping and complementary oligonucleotides into the vector pKK223-3. When expressed in E. coli, the recombinant protease was able to correctly process the HIV-1 core protein p24 from a beta-galactosidase-gag fusion protein and to use a heptapeptide as a substrate for proteolytic cleavage. A single base pair mutation was identified in a recombinant that resulted in the substitution of lysine for asparagine at position 88 and a significant loss of enzyme activity. Through site-directed mutagenesis, the Asn88 was changed to five other residues representative of all classes of amino acids. The correlation between enzyme activity and amino acid substitution suggests that the protease domain surrounding position 88 affects the protein's potential for forming an active homodimeric protein and hence, indicates a biochemical interaction that could be inhibited by novel antiviral compounds.

Amino Acid Sequence↗
PubMed1989

A model of orthopaedic dysfunction for clinical decision making in physical therapy practice.

This model serves as a framework for the critical analysis of current practice concepts. The analysis obtained from using this model should be integrated with other physiological systems of the body during examination and treatment processes. Currently used as a basis for graduate study in orthopaedic physical therapy, the model helps students identify fundamental research questions, compare various examination and treatment philosophies, and comprehend generic treatment goals and strategies.

Bone Diseases↗