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Biomedical subjects

R L Johnson

Publications and source records attributed to R L Johnson.

At least 145 records · Page 8Linked to original sources
PubMed1994

Design, synthesis, X-ray analysis, and dopamine receptor-modulating activity of mimics of the "C5" hydrogen-bonded conformation in the peptidomimetic 2-oxo-3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-1- pyrrolidineacetamide.

3(R)-(7a(S)-Hexahydro-1-oxo-3,3-dimethyl-1H-pyrrolo[1,2-c]imidazol-2-yl) - oxo-1-pyrrolidine-acetamide (2) and 3(R)-[1-(2,5-dioxopyrrolidino[3,4-c]piperazino)]-2-oxo-1- pyrrolidineacetamide (3) were designed and prepared as mimics of the "C5" hydrogen-bonded structure found in the crystal structure of 2-oxo-3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-1- pyrrolidineacetamide (1). Both compounds effectively restrict the psi 1 torsional angle to very near the value found in the X-ray structure of 1 as seen in the X-ray crystallographic determination of 2 and methyl 3(R)-[1-(2,5-dioxopyrrolidino[3,4-c]piperazino)]-2-oxo-1- pyrrolidineacetate (11), a diketopiperazine intermediate in the synthesis of 3. These analogs were tested for their ability to enhance the binding of the dopamine D2 receptor agonist N-propylnorapomorphine (NPA) in the absence and presence of 5'-guanylylimidodiphosphate (Gpp(NH)p). Both compounds enhanced [3H]-NPA binding in a dose-dependent manner by increasing both the binding affinity of the agonist and the number of high-affinity sites available for binding. Both 2 and 3 also attenuated the Gpp(NH)p-induced conversion of D2 receptor high-affinity states to the low-affinity states.

Amino Acid Sequence↗
PubMed1994

Comparison of myristoyl-CoA:protein N-myristoyltransferases from three pathogenic fungi: Cryptococcus neoformans, Histoplasma capsulatum, and Candida albicans.

Myristoyl-CoA:protein N-myristoyltransferase (Nmt) transfers myristate from CoA to the N-terminal Gly residue of cellular proteins in an ordered reaction mechanism that first involves binding of myristoyl-CoA to the apoenzyme. The gene encoding Saccharomyces cerevisiae Nmt1p (NMT1) is essential for vegetative growth. Candida albicans, Cryptococcus neoformans var. neoformans, and Histoplasma capsulatum are the principal causes of systemic fungal infections in immunocompromised humans. Metabolic labeling studies indicate that they synthesize a small set of cellular N-myristoylproteins during exponential growth on rich media, the most prominent of which co-migrate with two essential functionally interchangeable S. cerevisiae N-myristoylproteins, ADP ribosylation factor-1 (Arf1p) and Arf2p. NMT and ARF genes have been recovered from C. neoformans and H. capsulatum using the polymerase chain reaction. They are single copy genes, interrupted by multiple introns. C. neoformans and H. capsulatum Nmts have approximately 50% amino acid sequence identity with the orthologous S. cerevisiae, C. albicans, and Homo sapiens N-myristoyltransferases, whereas C. neoformans and H. capsulatum Arfs are approximately 80% identical with C. albicans Arf and S. cerevisiae Arf1p and Arf2p. Functional studies of C. neoformans and C. albicans Nmts conducted in Escherichia coli reveal that (i) both efficiently acylate S. cerevisiae Arf2p; (ii) C. neoformans Arf is a substrate for C. neoformans Nmt; and (iii) substitution of an Asp for a Gly located 5 residues from the C terminus of these two enzymes causes marked temperature-dependent reductions in their catalytic efficiency, just as it does with S. cerevisiae and H. sapiens Nmts. Wild type C. neoformans, C. albicans, and H. sapiens NMTs can fully complement the lethal phenotype of a S. cerevisiae nmt1 null allele at 24 and 37 degrees C when the GAL1-10 promoter controlling their expression is induced by galactose. Only the C. albicans enzyme is able to do so when the promoter is repressed with glucose. This complementation profile likely arises, at least in part, from differences in the protein substrate specificities of the orthologous Nmts. A Gly-->Asp mutation in S. cerevisiae, C. neoformans, C. albicans, and H. sapiens Nmts produces temperature-sensitive growth arrest in isogenic S. cerevisiae strains with a nmt1 null allele. Growth of strains producing the mutant C. albicans or H. sapiens, but not the C. neoformans, enzyme can be rescued by myristate at the non-permissive temperature (37 degrees C) even in the presence of cerulenin, an inhibitor of fatty acid synthetase.(ABSTRACT TRUNCATED AT 400 WORDS)

Acyltransferases↗
PubMed1994

The use of low-energy collisionally activated dissociation negative-ion tandem mass spectrometry for the characterization of dog and human urinary metabolites of the drug BW 1370U87.

Liquid chromatography (LC) combined with atmospheric pressure chemical ionization mass spectrometry was used to identify phase I and II metabolites of the drug BW 1370U87 in dog and human urine. Additional analysis of individual high-performance liquid chromatograph fractions collected from dog urine by combined gas chromatography/mass spectrometry identified one metabolite which was not detected by LC/MS methods. Using negative-ion LC/MS, the majority of BW 1370U87 metabolites in human urine were identified as glucuronic acid conjugates of phase I oxidative metabolites. The negative-ion fragmentation produced by low-energy collisionally activated decomposition (CAD), studied by tandem mass spectrometry experiments, confirmed that these compounds were drug-related and allowed metabolite structures to be assigned. Product-ion spectra of the metabolites were dominated by the loss of neutral molecules from even-electron deprotonated [M-H]- ions.

Animals↗
PubMed1994

Mechanisms of limb patterning.

The development of the vertebrate limb requires the coordinated action of multiple signals to achieve the proper arrangement of adult tissues. Recently, several molecules have been identified which play central roles in patterning of the limb bud. Sonic hedgehog, a homolog of the Drosophila segment polarity gene hedgehog, is likely to regulate anterior/posterior pattern formation. FGF-2 and FGF-4, members of the fibroblast growth factor family, have been shown to provide important signals for limb bud outgrowth and to indirectly regulate proximal/distal patterning. Some candidate effectors of the activity of Sonic hedgehog and of FGFs are known, including members of the clustered Hox genes.

Animals↗
PubMed1994

Sonic hedgehog: a key mediator of anterior-posterior patterning of the limb and dorso-ventral patterning of axial embryonic structures.

Sonic hedgehog is expressed in several sites during embryogenesis which are known to be important in directing the development of neighbouring tissues, including Hensen's node, the notochord, the floor plate of the neural tube, and the posterior of the limb bud. A unity in signalling mechanisms utilized by these inducers was first indicated because they all can provide a source of limb polarizing activity, assayed by grafting into the anterior of a limb bud. The hypothesis that they share a common signal is substantiated by the fact that they all express Sonic. Moreover, ectopic expression of Sonic in vivo suggests that it is responsible for the polarizing activity of the ZPA and plays an important role in dorso-ventral patterning of the spinal cord. The isolation of Sonic heralds a new era in the investigation of the molecular mechanisms of these key inductive interactions in vertebrate development.

Amino Acid Sequence↗
PubMed1994

Effect of high- versus moderate-intensity exercise on lymphocyte subpopulations and proliferative response.

The effect of 45 min of high- (80% VO2max) versus moderate- (50% VO2max) intensity treadmill exercise on circulating leukocyte and lymphocyte subpopulations, catecholamine and cortisol concentrations, and the mitogen-stimulated lymphocyte proliferative response was investigated in 10 well-conditioned (mean VO2max 66.0 +/- 1.9 ml/kg/min), young males (mean age 22.1 +/- 1.3 yrs). Blood samples were taken before and immediately after exercise, with three more samples taken during 3.5 h of recovery. Treatment order on the treadmill (graded walking at 7.3 +/- 0.1 km/h, 6.5 +/- 0.6% grade, versus level running at 16.1 +/- 0.3 km/h) was counterbalanced, with subjects acting as their own controls and results analyzed using a 2 x 5 repeated measures ANOVA. The concanavalin A- (Con A) stimulated lymphocyte proliferative response was decreased at 1 h and 2 h post-exercise relative to baseline levels following both exercise-intensity conditions. However, when adjusted on a per-T cell (CD3+) basis to account for the change in number of T cells in the in vivo assay, only the high-intensity exercise condition was associated with a 1-h post-exercise decrease (21%, p = 0.05) in the proliferative response relative to baseline. Exercise at 80% versus 50% VO2max resulted in significantly greater increases in cortisol and epinephrine concentrations, providing a physiological rationale for the immediate-post-exercise lymphocytosis, 1- to 3.5-h lymphocytopenia, and the decrease in Con A-stimulated lymphocyte proliferative response (per CD3+ cell) that occurred in greater measure following high-intensity exercise.

Adolescent↗
PubMed1994

Misleading hepatitis C serology following administration of intravenous immunoglobulin.

Intravenous immunoglobulin (IVIG) is a blood derivative that is being evaluated for the prevention and treatment of numerous disorders. Recent studies have suggested beneficial effects from the prophylactic administration of IVIG to very-low-birth-weight neonates. A disadvantage of such therapy is misleading infectious disease serologic assays following administration of IVIG. The authors report a recent case in their neonatal intensive care unit of a 24-week gestational age girl with a misleading positive hepatitis C serology reaction following IVIG administration.

False Positive Reactions↗
PubMed1994

Cardiopulmonary adaptations to pneumonectomy in dogs. III. Ventilatory power requirements and muscle structure.

Static and dynamic mechanical characteristics of the respiratory system were measured in five adult foxhounds 6-15 mo after right pneumonectomy (R-PNX) and in five matched foxhounds that underwent right thoracotomy without pneumonectomy (Sham). In R-PNX dogs, elastic recoil was lower than that in the left lung of Sham dogs. On exercise, absolute ventilatory power requirements of the lung and its components were measured, i.e., power requirements to overcome elastic and viscous resistances of the lung as well as power requirements during inspiration and expiration. All components were higher for a given minute ventilation in R-PNX dogs than in both lungs of Sham dogs. Ventilatory power requirements after R-PNX were also higher than in three adult foxhounds after left PNX studied previously by the same techniques. After R-PNX, the mass of the right costal diaphragm and total mass of inspiratory muscles were greater than in Sham dogs. There were no significant differences in ultrastructural features of the costal diaphragm. The unilateral increase in muscle mass is likely the result of chronic elevation and stretch of the right costal diaphragm after R-PNX.

Air Pressure↗
PubMed1994

Cardiopulmonary adaptations to pneumonectomy in dogs. IV. Membrane diffusing capacity and capillary blood volume.

Lung diffusing capacity for carbon monoxide (DLco) and its components, membrane diffusing capacity (Dmco) and capillary blood volume (Vc), as well as pulmonary blood flow (Qc), were measured at rest at several lung volumes and during treadmill exercise by a rebreathing technique in four adult dogs after right pneumonectomy (R-PNX) and in six matched control dogs (Sham) 6-12 mo after surgery. In both groups, lung inflation at rest was associated with a small increase in DLco and Dmco but not in Vc. After R-PNX, total DLco was lower by 30% at peak exercise compared with control values. When compared with DLco in a normal left lung, DLco in the remaining lung continued to increase along the normal relationship with respect to Qc up to a cardiac output equivalent to 34 l/min through both lungs of the Sham dog. There was no evidence of an upper limit of DLco being reached. The augmentation of DLco from rest to exercise was associated with corresponding increases in Dmco and Vc; after R-PNX, both Dmco and Vc continued to increase with respect to Qc along similar relationships as in control dogs without reaching an upper limit, suggesting a much larger alveolar-capillary reserve for gas exchange by diffusion than previously recognized. At higher levels of blood flow through the remaining lung, DLco was greater in adult dogs after R-PNX than after left pneumonectomy (Carlin et al. J. Appl. Physiol. 70: 135-142, 1991), suggesting that additional sources of compensation, e.g., lung growth, exist after removal of > 50% of lung.

Animals↗
PubMed1994

Family-centered care: thriving in Hawaii under Part H.

Hawaii's system of prevention and early intervention embodies Part H principles that a child with a disability is first surrounded by a family, then by a community. Since 1986, families in Hawaii have been active in early intervention, first by persuading the governor to name the Department of Health as the lead agency, and then by writing much of the original grant application, interviewing and selecting staff members, and serving on the Hawaii Early Intervention Coordinating Council and its subcommittees. Families helped develop Hawaii's broad definition of the population to be served and were vocal advocates before the legislature to obtain funding for the program. Under Part H, Hawaii serves 6% of all children under the age of three, a larger percentage than any other state. Services focus on the family's needs as much as on the child's. The Individualized Family Support Plan (IFSP), developed jointly by the parents and professionals, recognizes families as the final decision-maker on the IFSP team. Families choose options that fit their needs. IFSP meetings are at times and places convenient to families and, to the extent feasible, in the family's native language. Care coordinators, of whom several are parents of children with special needs, monitor services to ensure that families receive quality care. Families receive (1) services at no cost, (2) preference when applying for positions in the Zero-to-Three Hawaii Project, and (3) compensation when serving in advisory or policy-making areas. In Hawaii, families are the center of early intervention services.

Audiology↗
PubMed1994

Public trust: reclaiming or preserving?

The public trusts hospitals for their diagnostic and therapeutic capabilities, while resentful of the high costs of care. A comprehensive national health care program will increase the public's distrust of health care when its goals are not met. It is more desirable to incrementally add benefits in a national program beginning with a catastrophic coverage program to assure the public's trust.

Aged↗
PubMed1993

Sonic hedgehog mediates the polarizing activity of the ZPA.

The zone of polarizing activity (ZPA) is a region at the posterior margin of the limb bud that induces mirror-image duplications when grafted to the anterior of a second limb. We have isolated a vertebrate gene, Sonic hedgehog, related to the Drosophila segment polarity gene hedgehog, which is expressed specifically in the ZPA and in other regions of the embryo, that is capable of polarizing limbs in grafting experiments. Retinoic acid, which can convert anterior limb bud tissue into tissue with polarizing activity, concomitantly induces Sonic hedgehog expression in the anterior limb bud. Implanting cells that express Sonic hedgehog into anterior limb buds is sufficient to cause ZPA-like limb duplications. Like the ZPA, Sonic hedgehog expression leads to the activation of Hox genes. Sonic hedgehog thus appears to function as the signal for antero-posterior patterning in the limb.

Amino Acid Sequence↗
PubMed1993

Dopamine receptor modulation by a highly rigid spiro bicyclic peptidomimetic of Pro-Leu-Gly-NH2.

A peptidomimetic analogue of Pro-Leu-Gly-NH2 (PLG), compound 3, has been synthesized that contains a highly constrained spiro bicyclic type-II beta-turn mimic. Peptidomimetic 3 enhanced the binding of the dopamine receptor agonist ADTN to dopamine receptors by 40% at 10(-6) M. At this same concentration PLG enhanced the binding of ADTN by 26%. Like PLG, 3 exhibited a bell-shaped dose-response curve with the maximum effect occurring at a concentration of 10(-6) M. Because of the highly rigid nature of the spiro bicyclic type-II beta-turn constraint found in 3, these results lend strong support for the hypothesis that the biologically active conformation of PLG is a type-II beta-turn.

Amino Acid Sequence↗
PubMed1993

Relaxation by calcitonin gene-related peptide may involve activation of K+ channels in the human uterine artery.

The vasodilatory role of calcitonin gene-related peptide in activating K+ channels was examined in isolated, suffused human uterine arteries. Calcitonin gene-related peptide produced a concentration-dependent relaxation of norepinephrine (1 microM)-induced contractions. Calcitonin gene-related peptide was antagonized by glybenclamide (1-100 microM), an inhibitor of ATP-sensitive K+ channels, but not by tetraethylammonium (1 mM), an inhibitor of calcium(2+)-activated K+ channels. Glybenclamide (10 microM) produced a 6.7 fold and an 11-fold shift to the right of calcitonin gene-related peptide (0.1 to 100 nM) in uterine arteries from pregnant patients (n = 3) and nonpregnant patients (n = 6), respectively. Calcitonin gene-related peptide (10 nM) less effectively (P < 0.05) relaxed contractions produced by KCl (50 mM) (29.4 +/- 1.6%) than by norepinephrine and glybenclamide (10 microM) did not reverse this relaxation (22.2 +/- 6.8%, n = 4 nonpregnant patients). Pinacidil (1 microM), an ATP-sensitive K+ channel opener, relaxed norepinephrine-induced contractions of uterine arteries. Glybenclamide (10 microM) also antagonized pinacidil. These results suggest that calcitonin gene-related peptide relaxes norepinephrine-contracted human uterine arteries, at least in part, by activation of a K+ channel, perhaps of the ATP-sensitive type.

Adenosine Triphosphate↗