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Biomedical subjects

J A Adams

Publications and source records attributed to J A Adams.

At least 19 recordsLinked to original sources
PubMed1995

Phosphorylation modulates catalytic function and regulation in the cAMP-dependent protein kinase.

Site-directed mutagenesis was used to remove a critical phosphorylation site, Thr-197, near the active site of the catalytic subunit of cAMP-dependent protein kinase. This residue is present in a number of protein kinases, and its phosphorylation largely influences catalytic activity. We changed Thr-197 to aspartic acid and alanine and measured the effects of these substitutions on the kinetic mechanism and inhibitor affinities. The mutants were expressed as the free catalytic subunit and as soluble fusion proteins of glutathione-S-transferase. The values for KATP and Kpeptide for all three mutants are raised by approximately 2 orders of magnitude relative to the wild-type enzyme. Viscosometric measurements indicate that elevations in Kpeptide are the result of reduced rates for phosphoryl transfer and not reduced substrate affinities. This implies that the loop that contains the phosphothreonine, the activation loop, does not reduce access to the substrate site as proposed for the inactive forms of cdk2 kinase [DeBont, H. L., et al. (1993) Nature 363, 595-602] and MAP kinase [Zhang, F., et al. (1994) Nature 367, 704-711]. The mutants associate slowly with the wild-type regulatory subunit, although the cAMP-free wild-type regulatory subunit inhibits the mutants stoichiometrically. A mutant regulatory subunit that binds cAMP poorly and rapidly inhibits the wild-type catalytic subunit does not inhibit the mutant proteins. These data suggest that the phosphothreonine region serves as a docking surface for the regulatory subunit in the holoenzyme complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

A computer algorithm for differentiating valid from distorted pulse oximeter waveforms in neonates.

Current pulse oximeter technology is fraught with a significant false alarm rate. This is mainly due to motion artifacts at the sensor site which distort the pulse waveform and render the computation of SaO2 invalid. If the pulse waveform could be automatically recognized as either normal or distorted, then only valid SaO2 values would be displayed. We observed that the systolic upstroke time (Sy) of the pulse waveform has a narrow and consistent range in normal appearing pulses. The systolic upstroke time (Sy) is the time from the onset of systole to the peak of the pulse waveform. Comparison of a preset range of Sy was made against Sy obtained by computer analysis of each pulse waveform. Visual examination of 14,090 pulses was carried out to determine the sensitivity and false positive rate of the algorithm. Sensitivity of computer detection of valid pulses was 92% with a positive predictive value of 92%. When used on line for continuous recording of SaO2 in patients, this simple algorithm has the potential to decrease the false alarm rate of pulse oximeters and improve the accuracy of long-term SaO2 recordings.

Algorithms↗
PubMed1995

Diaphragmatic flutter in three babies with bronchopulmonary dysplasia and respiratory syncytial virus bronchiolitis.

Abnormalities of respiratory control, especially apnea, have been reported previously in infants with respiratory syncytial virus (RSV) infections. This is the first report of yet another abnormality of respiratory control, diaphragmatic flutter (DF), in infants with RSV infection. The presentation of these infants did not differ from the usual clinical presentation of RSV infection. While being monitored with respiratory inductive plethysmography for occurrences of apnea known to be common in RSV infection, DF was detected. This abnormality consisted of high frequency, diaphragmatic contractions which were intermittent in nature. They lasted no more than 4 days and were not associated with change in arterial oxygen saturation or heart rate. These infants were discharged free of DF and no further episodes have been observed over a 12-month period.

Administration, Inhalation↗
PubMed1995

Smoking cessation counseling in adults and children: the clinician's role.

Clinicians can profoundly improve the nation's health by implementing recently developed smoking cessation counseling strategies. Although not specifically validated for children and adolescents, young people are likely to benefit from many of the methods used successfully with adults. In the "minimal contact" setting of an office visit, clinicians can achieve substantial long-term quit rates by identifying all smokers through the medical chart, enlisting the help of ancillary personnel, focusing on patients who are ready to quit, and arranging follow-up. Physicians are more likely to be effective if they recognize that smoking cessation is a long-term process that may require multiple quit attempts for success. This article reviews office-based approaches to smoking cessation counseling, tobacco use prevention in children and adolescents, and pharmacologic treatment of nicotine addiction.

Adolescent↗
PubMed1994

Comparison of supine and prone noninvasive measurements of breathing patterns in fullterm newborns.

The current study was undertaken to ascertain whether shift from supine to prone posture alters the pattern of natural breathing in healthy fullterm newborns. Breathing patterns were measured in the supine and prone posture in 20 healthy fullterm infants using calibrated, noninvasive respiratory inductive plethysmography (RIP). The values for breathing pattern components in supine and prone postures expressed as means (+/- SD) were, respectively, tidal volume (VT), 14.1(+/- 3.2) and 18.9(+/- 4.9)mL; mean inspiratory flow 26.7(+/- 11.5) and 32.8(+/- 13.0)mL/s; and minute ventilation 232(+/- 75) and 288(+/- 96)mL/kg/min (P < 0.01). Less thoracoabdominal incoordination, expressed as the labored breathing index (LBI), occurred with shift from supine to prone posture in infants studied in the active behavioral stage, changing from 2.0(+/- 0.5) to 1.3(+/- 0.4) (P < 0.01). Placement of a facemask-pneumotachograph system increased VT measured with RIP by 26% in the supine, and 18% in the prone posture. Neither respiratory rate nor inspiratory time (Ti) changed with the postural shift. Therefore, change from supine to prone posture improved ventilation and increased respiratory drive as expressed by VT/Ti. Further, thoracoabdominal incoordination which took place during active sleep in the supine posture, lessened with change to the prone posture.

Humans↗
PubMed1994

cAMP-dependent protein kinase: crystallographic insights into substrate recognition and phosphotransfer.

The crystal structure of ternary and binary substrate complexes of the catalytic subunit of cAMP-dependent protein kinase has been refined at 2.2 and 2.25 A resolution, respectively. The ternary complex contains ADP and a 20-residue substrate peptide, whereas the binary complex contains the phosphorylated substrate peptide. These 2 structures were refined to crystallographic R-factors of 17.5 and 18.1%, respectively. In the ternary complex, the hydroxyl oxygen OG of the serine at the P-site is 2.7 A from the OD1 atom of Asp 166. This is the first crystallographic evidence showing the direct interaction of this invariant carboxylate with a peptide substrate, and supports the predicted role of Asp 166 as a catalytic base and as an agent to position the serine -OH for nucleophilic attack. A comparison of the substrate and inhibitor ternary complexes places the hydroxyl oxygen of the serine 2.7 A from the gamma-phosphate of ATP and supports a direct in-line mechanism for phosphotransfer. In the binary complex, the phosphate on the Ser interacts directly with the epsilon N of Lys 168, another conserved residue. In the ternary complex containing ATP and the inhibitor peptide, Lys 168 interacts electrostatically with the gamma-phosphate of ATP (Zheng J, Knighton DR, Ten Eyck LF, Karlsson R, Xuong NH, Taylor SS, Sowadski JM, 1993, Biochemistry 32:2154-2161). Thus, Lys 168 remains closely associated with the phosphate in both complexes. A comparison of this binary complex structure with the recently solved structure of the ternary complex containing ATP and inhibitor peptide also reveals that the phosphate atom traverses a distance of about 1.5 A following nucleophilic attack by serine and transfer to the peptide. No major conformational changes of active site residues are seen when the substrate and product complexes are compared, although the binary complex with the phosphopeptide reveals localized changes in conformation in the region corresponding to the glycine-rich loop. The high B-factors for this loop support the conclusion that this structural motif is a highly mobile segment of the protein.

Adenosine Diphosphate↗
PubMed1994

Examination findings in legally confirmed child sexual abuse: it's normal to be normal.

BACKGROUND: Studies of alleged victims of child sexual abuse vary greatly in the reported frequency of physical findings based on differences in definition of abuse and of "findings." This study was designed to determine the frequency of abnormal findings in a population of children with legal confirmation of sexual abuse, using a standardized classification system for colposcopic photographic findings. METHODS: Case files and colposcopic photographs of 236 children with perpetrator conviction for sexual abuse, were reviewed. The photos were reviewed blindly by a team member other than the examiner, and specific anatomical findings were noted and classified as normal to abnormal on a scale of 1 to 5. Historical and behavioral information, as well as legal outcome was recorded, and all data entered into a dBase III program. Correlations were sought between abnormal findings and other variables. RESULTS: The mean age of the patients was 9.0 years (range 8 months to 17 years, 11 months), with 63% reporting penile-genital contact. Genital examination findings in girls were normal in 28%, nonspecific in 49%, suspicious in 9%, and abnormal in 14% of cases. Abnormal anal findings were found in only 1% of patients. Using discriminant analysis, the two factors which significantly correlated with the presence of abnormal genital findings in girls were the time since the last incident, and a history of blood being reported at the time of the molest. CONCLUSIONS: Abnormal genital findings are not common in sexually abused girls, based on a standardized classification system. More emphasis should be placed on documenting the child's description of the molestation, and educating prosecutors that, for children alleging abuse: "It's normal to be normal."

Child↗
PubMed1992

Energetic limits of phosphotransfer in the catalytic subunit of cAMP-dependent protein kinase as measured by viscosity experiments.

Viscosogenic agents were used to test the diffusion limits of the reaction catalyzed by the catalytic subunit of the cAMP-dependent protein kinase. The effects of glycerol and sucrose on the maximum rate (kcat) and the apparent second-order rate constants (kcat/Kpeptide) for the phosphorylation of four peptidic substrates were measured at their pH optima. The agents were found to have moderate to no effect on kcat/Kpeptide for good and poor substrates, respectively. Conversely, kcat was highly sensitive to solvent viscosity for three of the four peptides at high concentrations of ATP. Taken together, these data indicate that enzymatic phosphorylation by the catalytic subunit proceeds with rapid or near rapid equilibrium binding of substrates and that all steps following the central substrate complex (i.e., chemical and conformational events) are fast relative to the rate-determining dissociation of product, ADP, when ATP levels are high. Under saturating concentrations of peptide I, LRRASLG, an unproductive form of the enzyme is populated. The observed phosphorylation rate from this complex is involved in rate limitation owing to a slow step separating unproductive and productive enzyme forms. The data are used to establish a kinetic mechanism for the catalytic subunit that predicts initial reaction velocities under varying concentrations of ATP and substrate.

Adenosine Triphosphate↗
PubMed1992

Sublethal effects of ethylene dibromide on wound healing and morphogenesis in Hydra oligactis.

Morphogenetic activity (budding region regeneration, foot regeneration, tentacle regeneration, spikes, separation, and waist) was observed in Hydra oligactis with two tandemly arranged gastric regions (2g hydras) following exposure to a commercial ethylene dibromide (EDB) mixture. First-stage budding hydras were selected for this study. Animals were deprived of food 24 h prior to grafting and observed at 24, 48, and 72 h after grafting. The artificial pond water (APW) group was not treated with any chemicals prior to grafting. The acetone/APW group was pre-exposed to a concentration of 20 mg/L of acetone/APW 24, 48, and 72 h prior to grafting and observed at 24 h intervals for a three-day period. The EDB: acetone/APW group was exposed to a mixture containing 5 mg/L of EDB and 15 mg/L acetone for 24, 48, and 72 h prior to grafting and observed at 24-hr intervals for three days. All animals were incubated at 19 +/- 2 degrees C. Ethylene dibromide caused a significant decrease in 2 degrees foot regeneration at the 72 h observation interval for animals pre-exposed to EDB for 48 and 72 h. There was also a significant correlation between pre-exposure and a decrease in the number of 2 degrees feet regenerated. Tentacle regeneration was significantly suppressed following a 24-h pre-exposure to EDB. Waists at the graft border significantly increased at the 48 and 72 h observation times and separation of the graft border appeared at 72 h after grafting following 72 h pre-exposure of the animals to the chemical.

Animals↗
PubMed1992

Detection of bone marrow metastases in neuroblastoma using a short term tissue culture technique.

AIMS: To improve detection of neuroblastoma metastases in the bone marrow: morphological evaluation of bone marrow is a routine and important component of the clinical staging of neuroblastoma and it depends on the successful identification of tumour cells which may only be present at extremely low levels. METHODS: Bone marrow mononuclear cells from patients with neuroblastoma were incubated in a simple suspension culture and examined regularly using an inverted objective microscope. In some cases cytospins of the cultured cells were examined further using morphological and immunocytological techniques. RESULTS: In some cultures spheroidal clumps of cells could be seen growing after only a few days. If the marrow was cultured for a longer period these spheroids continued to increase in size, became adherent to the stromal cell layer on the culture flask floor, and put out long characteristic processes (neurites). Morphological and immunocytological examination of cytospins from these cultures confirmed these cells as neuroblasts. CONCLUSIONS: This method has provided the sole evidence of marrow metastases in several newly diagnosed cases of neuroblastoma in which the bone marrow had shown no evidence of tumour using standard morphological and fluorescent immunocytological techniques. Although negative cultures do not preclude the presence of neuroblastoma, this method is a useful adjunct to the standard techniques.

Biopsy↗
PubMed1992

Hemodynamic effects of continuous negative extrathoracic pressure and continuous positive airway pressure in piglets with normal lungs.

The hemodynamic effects produced by continuous positive airway pressure (CPAP) and continuous negative extrathoracic pressure (CNEP) of 4 and 8 cm H2O were compared in 8 normal, spontaneously breathing piglets. Arterial blood gases and hemodynamic measurements were obtained before and during CPAP and CNEP of 4 and 8 cm H2O. CPAP 8 cm H2O and CNEP 8 cm H2O produced significant increases (p less than 0.01) in PaO2 from baselines 76 +/- 3 to 85 +/- 3 and 77 +/- 4 to 85 +/- 3 mm Hg, respectively. No significant changes occurred in PaCO2 or cardiac index, except during CPAP 8 cm H2O [38 +/- 1 to 44 +/- 2 mm Hg (p less than 0.05) and 376 +/- 30 to 330 +/- 30 ml/kg/min (p less than 0.05), respectively]. During CPAP of 4 cm H2O, significant increases occurred in mean right atrial pressure (Pra) (2.1 +/- 0.3 to 3.3 +/- 0.4 mm Hg; p less than 0.01), left ventricular end-diastolic pressure (LVEDP) (2.8 +/- 0.4 to 3.7 +/- 0.3 mm Hg; p less than 0.01), and mean pulmonary artery pressure (Ppa) (12.9 +/- 0.8 to 15.1 +/- 0.8 mm Hg; p less than 0.01). CPAP of 8 cm H2O produced marked increases in Pra (2.1 +/- 0.2 to 4.9 +/- 0.7 mm Hg; p less than 0.01), LVEDP (2.7 +/- 0.5 to 4.5 +/- 0.4 mm Hg; p less than 0.01) and Ppa (12.8 +/- 0.8 to 17.7 +/- 0.6 mm Hg; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Central and peripheral biogenic amine effects of brain missile wounding and increased intracranial pressure.

This study was performed to ascertain the acute effects of brain missile wounding on brain-stem and hypothalamic biogenic amines in a group of cats anesthetized with pentobarbital (40 mg/kg). Brain wounding is associated with a concomitant increase in intracranial pressure (ICP); to separate the effects of elevated ICP alone from the effects of wounding, a second group of cats had ICP artificially increased from a normal level of approximately 5 mm Hg to approximately 140 mm Hg by infusion of mock cerebrospinal fluid into the cisterna magna. In both groups, significant epinephrine depletions (47% to 74%) occurred in the nucleus tractus solitarius, area A1C1, locus ceruleus, raphe nuclei, and posterior hypothalamus. Epinephrine levels were also significantly decreased in the anterior hypothalamus in the wounded cats. In addition, both brain wounding and artificially induced ICP increases caused significant decreases of norepinephrine in the posterior hypothalamus, and of serotonin, 5-hydroxyindoleacetic acid, dopamine, and homovanillic acid in the raphe nuclei. Only brain wounding, however, caused significant reductions of norepinephrine, dopamine, and homovanillic acid in the nucleus tractus solitarius and area A1C1. The plasma catecholamine levels resulting from brain wounding or artificially induced ICP increases were dissimilar only in the amount of time required to attain maximum plasma levels, with the wounded animals responding faster. It is concluded that the hypothalamic and brain-stem biogenic amine changes resulting from either brain wounding or increased ICP alone are reflective of a stress response. Brain-stem distortion caused by brain wounding did not appear to be a factor and monoaminergic systems appeared to remain intact despite a severe and eventually lethal brain injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1991

The function of amino acid residues contacting the nicotinamide ring of NADPH in dihydrofolate reductase from Escherichia coli.

The importance of three amino acid residues contacting the nicotinamide ring of NADPH in Escherichia coli dihydrofolate reductase has been defined using site-directed mutagenesis and detailed steady-state and pre-steady-state kinetic experiments. Replacement of Tyr-100 with either glycine or isoleucine (Y100G or Y100I) disrupts an aromatic-aromatic interaction between the phenolic side chain and the nicotinamide ring. Both mutations remove the differential binding of the oxidized and reduced coenzymes implicating Tyr-100 as a major determinant for coenzyme specificity. Replacement of Ser-49 for alanine (S49A), designed to either displace or reduce the polarizability of a bound water molecule contacting the N1 of the nicotinamide ring, affects only the rate of release of NADP+. Replacement of Ile-14 with alanine (I14A), designed to alter both a weakly polar and a hydrogen bonding interaction with the periphery of the nicotinamide ring, affects only the binding of NADPH. Y100I, Y100G, and I14A all increase the activation barrier for the chemical step by approximately 2 kcal/mol. The lack of an effect for S49A suggests that water structure is not important for stabilizing the hydride transfer transition state. In addition, the nominal effects observed for these mutations disfavor the hypothesis that neighboring amino acid residues participate in the stabilization of the reaction transition state through polar or weakly polar contacts.

Amino Acids↗
PubMed1991

Angry about AIDS.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Role of flexible bronchoscopy and bronchoalveolar lavage in the diagnosis of pediatric acquired immunodeficiency syndrome-related pulmonary disease.

Flexible fiberoptic bronchoscopy with bronchoalveolar lavage was performed in 16 pediatric patients with the acquired immunodeficiency syndrome (AIDS) and deterioration in pulmonary function suggestive of opportunistic infection. In 62% of the patients Pneumocystis carinii was identified. Culture results showed a pure growth of Pseudomonas aeruginosa for one patient in addition to the Pneumocystis carinii. Bronchoscopy with lavage was well tolerated, with few complications even among patients with significant tachypnea and hypoxia. Because of its relative safety and effectiveness, this procedure should be considered the first invasive measurement used for evaluation of parenchymal lung disease in this population of patients.

Acquired Immunodeficiency Syndrome↗
PubMed1990

The enzymic nature of antibody catalysis: development of multistep kinetic processing.

Detailed kinetic investigations of a catalytic antibody that promotes the hydrolyses of an anilide and phenyl ester show that this catalyst uses a multistep kinetic sequence resembling that found in serine proteases to hydrolyze its substrates, although antibody was elicited to a single transition-state analog. Like the serine proteases the antibody catalyzes the hydrolysis reactions through a putative covalent intermediate, but unlike the enzymes it may use hydroxide ion to cleave the intermediates. Nevertheless, the antibody is a potent catalyst with turnover at higher pH values rivaling that of chymotrypsin. This analysis also reveals that turnover by the antibody is ultimately limited by product desorption, suggesting that improvements in catalytic efficiency may be achieved by judicious changes in the structure of the substrate, so that it is not superimposable on that of the eliciting hapten.

Acylation↗
PubMed1990

The kinetic mechanism of wild-type and mutant mouse dihydrofolate reductases.

A kinetic mechanism is presented for mouse dihydrofolate reductase that predicts all the steady-state parameters and full time-course kinetics. This mechanism was derived from association and dissociation rate constants and pre-steady-state transients by using stopped-flow fluorescence and absorbance measurements. The major features of this kinetic mechanism are as follows: (1) the two native enzyme conformers, E1 and E2, bind ligands with varying affinities although only one conformer, E1, can support catalysis in the forward direction, (2) tetrahydrofolate dissociation is the rate-limiting step under steady-state turnover at low pH, and (3) the pH-independent rate of hydride transfer from NADPH to dihydrofolate is fast (khyd = 9000 s-1) and favorable (Keq = 100). The overall mechanism is similar in form to the Escherichia coli kinetic scheme (Fierke et al., 1987), although several differences are observed: (1) substrates and products predominantly bind the same form of the E. coli enzyme, and (2) the hydride transfer rate from NADPH to either folate or dihydrofolate is considerably faster for the mouse enzyme. The role of Glu-30 (Asp-27 in E. coli) in mouse DHFR has also been examined by using site-directed mutagenesis as a potential source of these differences. While aspartic acid is strictly conserved in all bacterial DHFRs, glutamic acid is conserved in all known eucaryotes. The two major effects of substituting Asp for Glu-30 in the mouse enzyme are (1) a decreased rate of folate reduction and (2) an increased rate of hydride transfer from NADPH to dihydrofolate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗