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Biomedical subjects

R Chen

Publications and source records attributed to R Chen.

At least 559 records · Page 31Linked to original sources
PubMed1987

Nucleotide sequence of the gene for the peptidoglycan-associated lipoprotein of Escherichia coli K12.

During attempts to clone the gene for the Escherichia coli outer membrane protein III another gene was recovered. Its nucleotide sequence was determined and the deduced amino acid sequence showed that the gene does not encode protein III. It codes for a 173-residue polypeptide; 21 NH2-terminal residues are typical for a signal peptide. The sequence around the putative site (Ala-Cys) for removing this peptide, Ala-Ile-Ala-Ala-Cys-Ser-Ser-Asn, is highly homologous to that of the major cell envelope lipoprotein (Braun lipoprotein) surrounding its processing site; it is also homologous to the consensus pentapeptide Leu-Leu-Ala-Gly-Cys present in other lipoproteins of gram-negative bacteria. It could be shown that the gene expresses a lipoprotein with all the properties, including the amino acid composition, of the peptidoglycan-associated lipoprotein (PAL) [Mizuno, T. (1979) J. Biochem. (Tokyo) 86, 991-1000]. Therefore, the cloned gene is the pal gene. The protein does not contain hydrophobic regions which would serve as a membrane anchor. Tandemly repeated amino acid sequences exist at and near the NH2-terminus of the mature protein which are homologous to such repeats in the Braun lipoprotein, suggesting a common origin of this part of the two proteins. Attempts to place a transposon into the pal gene were unsuccessful. Hence the complete absence of the protein may be lethal and its function remains unknown.

Amino Acid Sequence↗
PubMed1987

The relative efficiency of the sets and the cusum techniques in monitoring the occurrence of a rare event.

The efficiency of each of two methods for monitoring the occurrence of a rare event, the cusum, carried out monthly, and the sets techniques, was assessed by use of simulated datasets. The monthly cusum parameters used in this study were those recommended for monitoring of birth defects in a monthly analysis. The sets technique parameters, recommended for monitoring of low-level epidemics, were adjusted to match the average interval between false alarms to the corresponding values observed for the monthly cusum technique. The results indicate that the relative efficiency of the two techniques depends on the baseline frequency of diagnoses. The sets technique is shown to be more efficient than monthly cusum when the number of cases expected in a year is no greater than five, but less efficient otherwise. In the former case, lengthening the interval between cusum analyses can make the cusum technique more efficient than the sets technique. This possibility deserves further exploration and could affect future recommendations.

Adult↗
PubMed1987

Controlled follow-up of patients released by a review panel at one and two years after separation.

Fifty patients released by the Review Panel are compared with a matched group of 50 patients discharged by the attending physician at one and at two years after separation from hospital. The two groups did not differ with respect to readmission rate or time spent in the community. At two years the physician-discharged patients were functioning better than the Panel-discharged patients in two of the seven areas of functioning; in the other five areas of functioning the adjustment of the two groups did not differ. The implications of these findings for the operation of the Review Panel and for the timely discharge of involuntary patients by attending physicians is discussed.

Adult↗
PubMed1987

An internal clock reaction used in a one-step enzyme immunochromatographic assay of theophylline in whole blood.

We describe the development and performance of a second-generation enzyme immunochromatography method for visually quantifying theophylline in whole blood without the use of instrumentation. We have developed the novel concept of an internal chemical clock reaction to combine the capillary-migration and color-generation protocol of the two-step immunochromatographic assay into a single-step, simultaneous protocol. The two assay components are (a) chromatographic paper to which glucose oxidase (EC 1.1.3.4) and monoclonal antibody to theophylline have been immobilized, and (b) an enzyme reagent consisting of glucose, dicarboxidine, ascorbate, and theophylline-labeled horseradish peroxidase (EC 1.11.1.7). The ascorbate acts as an internal clock by inhibiting premature color formation until the ascorbate has been completely consumed in the peroxidase-mediated reaction. Color is then generated rapidly, producing a clearly visible front on the paper. Performance evaluations of the 20-min one-step assay show very good precision, analytical recovery, specificity, and accuracy. This simplified protocol is reliable and convenient for therapeutic drug monitoring in the physician's office.

Antibodies, Monoclonal↗
PubMed1986

The glutamate analogue quisqualic acid is neurotoxic in striatum and hippocampus of immature rat brain.

To assess the neurotoxic properties of the glutamate agonist quisqualic acid (QA) in immature brain, we injected this compound (100 nmol QA/1 microliter) directly into the striatum of 7-day-old rats. QA produced neuronal necrosis and glial infiltration in 14 pups and reduced the size of the striatum and hippocampus on the side of injection. Intracerebral injection of QA provides a new method for producing neuronal lesions in the developing brain.

Animals↗
PubMed1986

Characterization of glycoprotein hormone free alpha-subunit from human pituitary and placenta extracts.

Standard alpha-subunit dissociated from glycoprotein hormones differs from individual (free) alpha-subunit found in sera or in cell culture media; secreted free alpha-subunit is larger, more acidic and lacks the ability of recombining in vitro with standard hCG-beta. It is unclear whether the large free alpha-subunit is only a secretory product or whether it is also present in tissue. Herein were studied the molecular size, the isoelectric pH, and the recombining activity of free alpha-subunit obtained from pituitary and placenta extracts. Sephadex exclusion chromatography showed the presence of both a large and a small form, and a changing large/small free alpha-subunit ratio in the various extracts. Most of the large form obtained from placenta extracts electrofocused into two peaks of pI 4.8 and 5.1. The large form showed no recombining activity with standard hCG-beta while the small free alpha-subunit recombined as well as did standard hCG-alpha. The observation of three common characteristics (a larger size, a pI 4.8, and a lack of recombining activity) suggests a similarity between the large secreted form and a fraction of the free alpha-subunit in tissue.

Chromatography, Gel↗
PubMed1985

Synthesis and antifertility activity of zoapatanol analogues.

The synthesis of and guinea pig contragestational screening data for several oxepane and 3,8-dioxabicyclo[3.2.1]octane analogues of zoapatanol (1) are described and their structure-activity relationships discussed. Conversion of the 5-keto group on the nonenyl side chain of 1 into a hydroxyl function enhanced the potency. Further significant enhancement in the potency was realized with the transformation of several oxepanes into the 3,8-dioxabicyclo-[3.2.1]octane-1-acetic acid derivatives. Detailed, comparative contragestational evaluation of the three most potent compounds 9, 33, and 37 is presented, which led to the selection of 33 (ORF 13811) for further biological evaluation.

Abortifacient Agents↗
PubMed1984

Congenital cardiac anomalies associated with the DiGeorge syndrome: a neonatal experience.

The DiGeorge syndrome is a rare congenital abnormality of absent of hypoplastic thymus and parathyroid glands. Thirty neonates who had cardiac lesions and the DiGeorge syndrome are reviewed. The early mortality for 10 neonates undergoing palliative procedures was 80%. Seventy-five percent of the deaths were secondary to sepsis. Twenty neonates did not undergo palliative procedures. In this group, early mortality was 60% and late mortality was 65%. Sixty percent of the deaths in this group were associated with sepsis, with cardiac failure responsible for the remaining deaths. Survival in both groups has improved with appropriate treatment of the immunological and metabolic consequences of the DiGeorge syndrome.

Abnormalities, Multiple↗
PubMed1984

Ultrasound-accelerated immunoassay, as exemplified by enzyme immunoassay of choriogonadotropin.

The rate-limiting step in many solid-phase immunoassays is associated with the slow kinetics of binding of macro-molecular antigen and conjugate to the immobilized phase. We demonstrate that the use of ultrasonic energy to enhance mass transport across liquid/solid interfaces can dramatically accelerate antigen binding to immobilized antibodies. We use an ultrasound-accelerated procedure with an enzyme-channelling test strip containing glucose oxidase and specific antibody to the alpha-subunit of human choriogonadotropin (HCG) co-immobilized onto a cellulose support. A horseradish peroxidase conjugate of monospecific antibody to the beta-subunit of HCG is used in the liquid phase to complete the immune "sandwich." Use of ultrasound to accelerate binding and of enzyme channelling to eliminate wash steps result in a simple two-incubation protocol by which 25 int. units of urinary HCG per liter can be detected visually in less than 20 min of assay time.

Chorionic Gonadotropin↗
PubMed1983

Disposition of phencyclidine after intramuscular administration.

The disposition of radioactive phencyclidine (PCP) in various rat tissues, after single or repeated intramuscular injections for 23 days, have been investigated. Peak levels of radioactivity appeared 45-90 min after a single administration. The pancreas, salivary glands and mesenteric fat contained 4 to 6-fold higher radioactivity than brain, muscles, tendons, and bones. After repeated 3H-PCP injections, radioactivity levels showed a similar pattern as to that of the peak levels after a single administration, but at notably higher values. On the other hand, the percentage of depletion, within 48 h after the final injection, was the highest in the pancreas, salivary glands and mesenteric fat. It is possible that despite the low retention capacity of PCP radioactivity per unit weight of muscle, tendon and bone, they may be considered important reservoirs for either PCP, or its metabolites or both because of their large relative mass in the body.

Animals↗
PubMed1983

Clinical characteristics and results of electrophysiologic testing in young adults with ventricular tachycardia or ventricular fibrillation.

Thirty-one patients 16 to 40 years of age (mean +/- SD = 30.7 +/- 7 years) had one or more episodes of sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Underlying cardiac abnormalities consisted most commonly of cardiomyopathy (nine), long QT syndrome (LQTS) (five), and mitral valve prolapse (five); no identifiable heart disease was found in four patients. Programmed ventricular stimulation induced VT in only one of four patients with the LQTS but induced VT in 64% of 22 patients with other abnormalities. Chronic drug treatment was based either on serial electropharmacologic testing or was empiric when electrophysiologic testing failed to provoke an arrhythmia. Using this approach, we found a 13% incidence of recurrent VT and a 10% mortality over a follow-up period of 18.1 +/- 13.9 months. In young adults with VT or VF, an underlying cardiac abnormality can usually be found. Extensive evaluation should be performed to uncover the underlying cardiac abnormality as this may influence chronic management.

Adolescent↗