Search PubMed⌕ Search

Biomedical subjects

J L Smith

Publications and source records attributed to J L Smith.

At least 217 records · Page 12Linked to original sources
PubMed1994

Preliminary X-ray analysis of Escherichia coli GMP synthetase: determination of anomalous scattering factors for a cysteinyl mercury derivative.

We have initiated a project to determine the three-dimensional structure of GMP synthetase (GMPS) from Escherichia coli. GMPS catalyzes the conversion of XMP to GMP in the final step of de novo guanine nucleotide biosynthesis, and is a member of the glutamine amidotransferase family: a group of enzymes responsible for the assimilation of nitrogen into compounds such as amino acids, purine and pyrimidine bases, amino sugars, and antibiotics. The E. coli guaA gene encoding GMPS was cloned into a tac expression vector, overexpressed, and its gene product purified. Conditions for the growth of protein crystals were developed using recombinant GMPS in the presence of MgCl2, ATP, and XMP. The crystals are monoclinic, space group P2(1), with cell parameters of a = 156.0 A, b = 102.0 A, c = 78.8 A, beta = 96.7 degrees. Diffraction data to 2.8 A spacings were collected on a Xuong-Hamlin area detector with an overall Rsym of 5.2%. Both the volume of the unit cell and the peaks in the self-rotation function are consistent with one GMPS tetramer of D2 symmetry in the crystallographic asymmetric unit. Previously, GMPS has been observed only as a dimer in solution. GMPS was covalently modified with p-chloromercuribenzylsulfonic acid (PCMBS), and its X-ray fluorescence spectrum was measured through the LIII absorption edge of mercury. Anomalous scattering factors for cysteinyl mercury were derived from this spectrum, and the feasibility of structure determination by multi-wavelength anomalous diffraction was evaluated. The optimal MAD dispersive signal is 4.5% of magnitude of F, and the optimal MAD Bijvoet signal is 7.5% of magnitude of F at a concentration of approximately 1 mercury per 10-kDa protein. The anomalous scattering factors tabulated here should be transferable to cysteinyl mercury in other proteins.

Base Sequence↗
PubMed1994

Metabolism and excretion of methylamines in rats.

Experiments were performed with rats to examine the sources and disposition of dimethylamine (DMA), trimethylamine (TMA), and trimethylamine N-oxide (TMAO), all potential substrates for in vivo nitrosation to form N-nitrosodimethylamine (NDMA), a potent carcinogen. When bolus doses of [14C]DMA or [14C]TMA were given ip, recovery of radioactivity in the urine was essentially complete, and respiratory excretion, fecal excretion, and accumulation in tissues of these amines or their metabolites were negligible. Urine analysis following doses of stable isotopes showed that DMA was not converted to TMA or TMAO. Varying amounts of TMA were oxidized to TMAO, the fraction oxidized decreasing at higher doses of TMA. Ingestion and excretion of naturally occurring methylamines were monitored over a 5-day period in separate groups of normal and germ-free rats. The results of these metabolic balance studies indicate that there is net synthesis of DMA by gut bacteria and net consumption of TMAO by endogenous processes. The net intake or excretion of TMA and TMAO observed in normal and germ-free rats is consistent with bacterial synthesis of TMA followed by its almost complete oxidation to TMAO. Blood concentrations of DMA and TMA were measured in rats for 8 hr following < 5, 100, or 1000 mumol bolus i.v. or ip doses of radioisotopes or stable isotopes. At any given dose of DMA or TMA, the decay in blood concentration was approximately monoexponential. At the lowest (most physiologic) dose the apparent volume of distribution (VD) for DMA was larger than that for TMA. Both values of VD greatly exceeded the size of the animals, suggesting that DMA and TMA are highly concentrated at one or more locations in the body. This was confirmed by measurements in tissue homogenates sampled 1 hr after a dose. The overall handling of methylamines by rats is generally consistent with observations in humans. The presence of high local concentrations of DMA and TMA at various extragastric sites merits further investigation in connection with the potential for endogenous nitrosation of these methylamines to form NDMA.

Animals↗
PubMed1994

Coordination between head and hindlimb motions during the cat scratch response.

Coordination between motions of the head and the hindlimb paw ipsilateral to the stimulated pinna were assessed during the scratch cycle in freely moving cats. Motor patterns were determined by electromyographic (EMG) recordings made from epimysial-patch electrodes surgically implanted on the biventer cervicis (BC), complexus (CM), obliquus capitis inferior (OC), and splenius (SP) muscles and by fine-wire EMG electrodes implanted in two ankle muscles, medial gastrocnemius (MG), and tibialis anterior (TA). To assess head motions during the three phases of the scratch cycle (precontact, contact, postcontact), several responses were filmed, and in some cats an in vivo force transducer was implanted on an ankle extensor muscle (MG or plantaris, PL) to determine the tension profile during the scratch cycle. During the scratch cycle, the head's trajectory was usually characterized by a small oscillation in which the head was pushed away during paw contact (as hindlimb joints extended) and then repositioned during the noncontact phases (as hindlimb joints flexed). Neck muscle activity did not occur during all responses or during all cycles of a single multicycle scratch response, and when it occurred, neck muscle EMG was characterized as phasic (a single burst during the cycle) or tonic (low-level activity during the entire cycle). Neck muscles ipsilateral (i) to the scratching limb exhibited phasic bursts more than contralateral (c) muscles, and phasic activity was most frequently observed in the iBC, iSP, iOC, and cOC muscles. The cOC was reciprocally active with the ipsilateral muscles, and its burst coincided with the postcontact phase and the ankle flexor (TA) burst. The ipsilateral muscles (iOC, iSP, iBC) were active during paw contact, and the termination of all three bursts occurred synchronously just after peak tension of the ankle extensor was reached. The iBC was active before the onset of paw contact and may have been responsible for repositioning the head, along with the cOC, during the precontact phase. The iOC became active after the onset of paw contact (22 ms) and was recruited more often when the peak extensor tendon force was high (10-16 N). The iSP, in contrast, was active during the contact phase of most scratch cycles examined and its recruitment appeared to be unrelated to tendon forces. Our data suggest that phasic neck muscle activity is not obligatory during the cat scratch response, but is related to certain conditions such as a higher than average tendon force of an ankle extensor during contact and the need to reposition the head during the noncontact phases of the cycle.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Structural aspects of the cytochrome b6f complex; structure of the lumen-side domain of cytochrome f.

The following findings concerning the structure of the cytochrome b6f complex and its component polypeptides, cyt b6, subunit IV and cytochrome f subunit are discussed: (1) Comparison of the amino acid sequences of 13 and 16 cytochrome b6 and subunit IV polypeptides, respectively, led to (a) reconsideration of the helix lengths and probable interface regions, (b) identification of two likely surface-seeking helices in cyt b6 and one in SU IV, and (c) documentation of a high degree of sequence invariance compared to the mitochondrial cytochrome. The extent of identity is particularly high (88% for conserved and pseudoconserved residues) in the segments of cyt b6 predicted to be extrinsic on the n-side of the membrane. (2) The intramembrane attractive forces between trans-membrane helices that normally stabilize the packing of integral membrane proteins are relatively weak. (3) The complex isolated in dimeric form has been visualized, along with isolated monomer, by electron microscopy. The isolated dimer is much more active than the monomer, is the major form of the complex isolated and purified from chloroplasts, and is inferred to be a functional form in the membrane. (4) The isolated cyt b6f complex contains one molecule of chlorophyll a. (5) The structure of the 252 residue lumen-side domain of cytochrome f isolated from turnip chloroplasts has been solved by X-ray diffraction analysis to a resolution of 2.3 A.

Amino Acid Sequence↗
PubMed1994

On-table diagnosis of incipient carotid artery thrombosis during carotid endarterectomy by transcranial Doppler scanning.

We present a case where transcranial Doppler ultrasound monitoring of a carotid endarterectomy enabled us to detect the incipient thrombosis of the operated artery before reversal of anesthesia. The use of transcranial Doppler ultrasound monitoring in carotid endarterectomy has the potential to detect this complication before serious neurologic damage has occurred and therefore reduce the morbidity and mortality rates associated with the operation.

Aged↗
PubMed1994

Visual morbidity in giant cell arteritis. Clinical characteristics and prognosis for vision.

PURPOSE: To characterize visual morbidity in giant cell arteritis and to assess prognosis with respect to treatment. METHODS: Record review of 185 patients with coded diagnosis of giant cell (cranial) arteritis examined at the Bascom Palmer Eye Institute from January 1, 1980, to January 31, 1993. RESULTS: Forty-five patients with biopsy-proven giant cell arteritis had visual symptoms, and 41 individuals (63 eyes) lost vision. The visual loss was unilateral in 19 patients (46%), sequential in 15 (37%), and simultaneous in 7 (17%). Anterior ischemic optic neuropathy developed in 88% of eyes, visual acuity was 20/200 or worse in 70%, 21% had no light perception, and the majority of field defects in testable eyes, aside from central scotomas associated with loss, showed altitudinal or arcuate patterns. Six patients lost vision during corticosteroid therapy for systemic symptoms of giant cell arteritis, whereas in 39 patients visual symptoms prompted steroid treatment. For visual symptoms, 25 patients received intravenous methylprednisolone, whereas 20 received oral prednisone alone. In the 41 patients with visual loss, vision was unchanged in 20 (49%), it worsened in 7 (17%), and it improved in 14 (34%). Subsequent fellow eye involvement was observed only with oral therapy, and a greater percentage of patients (9/23 [39%] versus 5/18 [28%]) improved after intravenous treatment. CONCLUSIONS: In the authors' series, patients with visual loss due to giant cell arteritis had a 34% chance for some improvement in visual function after corticosteroid treatment. Intravenous therapy may diminish the likelihood of fellow eye involvement and was associated with a slightly better prognosis for visual improvement.

Administration, Oral↗
PubMed1994

Atwater to the present: what have we learned about our food supply?

In the one hundred years since W. O. Atwater produced the first food composition tables for the U.S. food supply, many changes have occurred in the food supply. These changes reflect improvements in agricultural and food processing practices which have resulted in an ever increasing variety of foods available for consumption. Maintaining a food composition database for such a food supply requires priority setting decisions and collaboration between government, private sector and academic entities. Designing appropriate food composition databases requires knowledge of how these data will be used. Information about data source, variability, brand specificity and analytical methodology are among the important factors to be considered.

Databases, Factual↗
PubMed1994

Assessment of proliferative activity in leukaemic bone marrow using the monoclonal antibody Ki-67.

AIMS: To investigate proliferative activity in leukaemic and lymphomatous bone marrow infiltrates and to assess the feasibility of transport of specimens among institutions. METHODS: Proliferative activity in bone marrow trephine cryosections from 99 patients with non-Hodgkin's lymphoma (NHL), 23 patients with acute myeloid leukaemia (AML), 11 with acute lymphoblastic leukaemia (ALL), and two with acute undifferentiated leukaemia (AUL) was investigated. Infiltration was seen in 52 out of 99 cases of NHL on bone marrow cryosections. A score was devised to assess pathological infiltrates in bone marrow trephine cryosections using the monoclonal antibody Ki-67. This method of scoring gave a measure of non-erythroid proliferative activity. RESULTS: Mean Ki-67 positivity in bone marrow infiltrates in 31 low grade B cell lymphomas (Kiel classification) was 0.3% before and 4.7% after treatment, 16.4% in seven high grade B cell lymphomas, and 17.8% in 12 peripheral T cell lymphomas. In 48 cases of NHL, bone marrow cryosections had not been infiltrated, and in all but one case the percentage of Ki-67 positive cells in normal marrow was less than 3%; the remaining case showed coexistent myelodysplasia and 8% bone marrow Ki-67 positivity. In eight cases of common ALL at diagnosis, the mean Ki-67 positivity in marrow cryosections was 24.9%, significantly higher than the 2.4% Ki-67 positivity seen in AML (p < 0.05). One of the two cases of common ALL with less than 1% Ki-67 positivity was refractory to treatment. CONCLUSIONS: Proliferative activity of erythroid elements in the bone marrow varies greatly. Immunostaining of bone marrow cryosections using Ki-67 permits accurate assessment of non-erythroid proliferative activity in lymphomas and leukaemia. High grade B cell lymphomas and peripheral T cell lymphomas invading the marrow have very similar mean proliferative activities. Such levels of proliferation are of the same order as those seen in common ALL, but much higher than those seen in AML.

Adult↗
PubMed1994

Significant activity of paclitaxel in advanced transitional-cell carcinoma of the urothelium: a phase II trial of the Eastern Cooperative Oncology Group.

PURPOSE: To assess the efficacy and toxicity of single-agent paclitaxel as first-line chemotherapy in patients with locally advanced or metastatic transitional-cell carcinoma of the urothelium. PATIENTS AND METHODS: Twenty-six eligible patients were enrolled onto this cooperative group study and treated with paclitaxel at a dosage of 250 mg/m2 by 24-hour continuous infusion every 21 days until progression or patient intolerance. All patients received recombinant human granulocyte colony-stimulating factor (rhG-CSF) at 5 micrograms/kg/d for at least 10 days during each cycle. RESULTS: Eleven of 26 patients (42%; 95% confidence interval [CI], 23% to 63%) demonstrated an objective response, with seven achieving a complete clinical response (CR) (27%; 95% CI, 12% to 48%) and four (15%) a partial response (PR). The median duration of response in the 11 responders is 7+ months (range, 4 to 17), with five responders (four CRs, one PR) remaining progression-free at 5, 6, 10, 12, and 16 months from the start of therapy. The estimated median survival duration for all patients is 8.4 months. Hematologic toxicity consisted of anemia (12% grade 3) and granulocytopenia (4% grade 3, 19% grade 4), with two patients developing granulocytopenic fevers. Nonhematologic toxicity included grade 3 mucositis in 11%, grade 3 neuropathy in 11%, and grade 4 diarrhea in 4%. CONCLUSION: Single-agent paclitaxel at this dosage and schedule is one of the most active single agents in previously untreated patients with advanced urothelial carcinoma, and is well tolerated by this patient population when given with hematopoetic growth factor support.

Adult↗
PubMed1994

Polymerase chain reaction amplification analyses of clonality in T-cell malignancy including peripheral T-cell lymphoma.

Clonality in T-cell malignancy was investigated using T-cell receptor (TcR) V beta 1-20 family primers and polymerase chain reaction amplification (PCR) of cDNA prepared from tissue biopsies and blood involved with tumour. Secondary PCR amplification of the VDJ joints of primary PCR products was performed to distinguish clonal from polyclonal products, and clonal V beta gene products were confirmed by direct PCR sequencing in the majority of cases. In eight T-cell malignancies including T-cell acute lymphoblastic leukaemia (T-ALL) and T-cell chronic lymphocytic leukaemia (T-CLL) shown to be clonal by Southern blot analysis, one or two primary PCR products were identified and shown to be clonal. In five cases of peripheral T-cell lymphoma (PTCL) all V beta 1-20 families were identified after primary PCR amplification, and clonal products were identified in two cases after secondary amplification; TcR V beta clonal families could not be demonstrated in the remaining three cases. These data were in agreement with previous Southern blot analysis of these cases, and confirmed the presence of reactive T cells in PTCL as well as providing further evidence for the genotypic heterogeneity of this entity. In the remaining case, a blood lymphocytosis, primary PCR amplification produced predominant TcR V beta 6 and V beta 12 family products, of which the V beta 6 family proved clonal after secondary PCR amplification. There was no evidence for overrepresentation of TCR V beta families by the tumour populations in this study, furthermore the data confirm the involvement of reactive cells in T-cell malignancy and the genetic heterogeneity of PTCL.

Base Sequence↗
PubMed1993

Alteplase versus heparin in acute pulmonary embolism: randomised trial assessing right-ventricular function and pulmonary perfusion.

Data from a non-randomised study have hinted that in patients with acute pulmonary embolism (PE), thrombolysis followed by heparin more rapidly reverses right-ventricular dysfunction and restores pulmonary tissue perfusion than does heparin alone. We have pursued this idea in a randomised protocol. 46 haemodynamically stable patients were randomised to recombinant tissue plasminogen activator (alteplase, rt-PA) 100 mg over 2 h followed by intravenous heparin and 55 to heparin alone. Right-ventricular wall motion was assessed qualitatively, and right-ventricular end diastolic area was estimated by planimetry from echocardiograms at baseline and at 3 and 24 hours. Pulmonary perfusion scans were obtained at baseline and 24 hours. In 39% of rt-PA patients but in only 17% of heparin alone patients right-ventricular wall motion at 24 hours had improved from baseline and in 2% and 17%, respectively, it worsened (p = 0.005). rt-PA patients also had a significant decrease in right-ventricular end-diastolic area during the 24 hours after randomisation and a significant absolute improvement in pulmonary perfusion (14.6% vs 1.5%). No clinical episodes of recurrent PE were noted among rt-PA patients, but there were 2 fatal and 3 non-fatal clinically suspected recurrent PEs within 14 days in patients randomised to heparin alone. rt-PA rapidly improves right-ventricular function and pulmonary perfusion among patients with PE and may lead to a lower rate of adverse clinical outcomes.

Acute Disease↗
PubMed1993

Trypanosoma vivax: evidence for only one RNA polymerase II largest subunit gene in a trypanosome which undergoes antigenic variation.

Previous studies suggested a correlation between antigenic variation in Kinetoplastida and the presence of two RNA polymerase (pol) II largest subunit genes in these organisms. We have found that Trypanosoma vivax, an African trypanosome which undergoes antigenic variation, is an exception, and has only one pol II largest subunit gene, indicating that probably neither of the two pol II genes found in other African trypanosomes is uniquely required for antigenic variation.

Animals↗
PubMed1993

Gait-related motor patterns and hindlimb kinetics for the cat trot and gallop.

To assess speed- and gait-related changes in semitendinosus (ST) activity, EMG was recorded from three cats during treadmill locomotion. Selected step cycles were filmed, and hip and knee joint kinematics were synchronized with EMG records. Swing-phase kinetics for trot and gallop steps at 2.25 m/s were compared for gait-related differences. Also, swing kinetics for different gallop forms were compared. With few exceptions, ST-EMG was characterized by two bursts for each step cycle; the first preceded paw off (STpo), and the second preceded paw contact (STpc). The two-burst pattern for the walk was defined by a high-amplitude STpo burst and a brief, low-amplitude STpc burst; at the slowest walk speeds, the STpc burst was occasionally absent. For the trot, the STpo burst was biphasic, with a brief pause just after paw off. With increasing walk-trot speeds, the duration of both bursts (STpo, STpc) remained relatively constant, but recruitment increased. Also, the onset latency of the STpo burst shifted, and a greater proportion of the burst was coincident with knee flexion during early swing. At the trot-gallop transition, there was an abrupt change in the two-burst pattern, and galloping was characterized by a high-amplitude STpc burst and a brief, low-amplitude STpo burst. At the fastest gallop speeds, the STpo burst was often absent, and the reduction in or elimination of the burst was associated with a unique pattern of swing phase kinetics at the knee. Knee flexion during the gallop swing was sustained by two inertial torques related to hip linear acceleration (HLA) and leg angular acceleration (LAA); correspondingly, muscle contraction was unnecessary. Conversely, knee flexion at the onset of the trot swing relied on a flexor muscle torque at the knee acting with an inertial flexor torque (LAA). Rotatory and transverse gallops at 4.0 m/s had similar swing phase kinetics and ST-EMG. Gait-related changes in ST-EMG, particularly at the trot-gallop transition, are not congruent with neural models assuming that details of the ST motor pattern are produced by a spinal CPG. We suggest that motor patterns programmed by the spinal CPG are modulated by input from supraspinal centers and/or motion-related feedback from the hindlimbs to provide appropriate gait-specific activation of the ST.

Animals↗
PubMed1993

Fluorescein angiography in the diagnosis of giant cell arteritis.

Clinical data and fundus fluorescein angiograms were analyzed from 35 patients with acute (onset less than four weeks) anterior ischemic optic neuropathy. Nineteen of the 35 patients (54%) had nonarteritic disease, and 16 patients (46%) had giant cell arteritis confirmed by biopsy. Patients with arteritis had higher erythrocyte sedimentation rates, larger cup/disk ratios, and delayed fluorescein dye appearance and choroidal filling times. Three additional patients with cranial arteritis confirmed by biopsy, but without visual loss, had angiographic characteristics similar to patients with arteritic ischemic neuropathy. We consider fluorescein angiography a valuable diagnostic adjunct in identifying patients with giant cell arteritis.

Adrenal Cortex Hormones↗
PubMed1993

Pulmonary microvascular fat: the significance?

OBJECTIVE: To determine the effects of fat emboli on cardiopulmonary function in critically ill patients. DESIGN: A prospective study. SETTING: Tertiary referral medical/surgical shock/trauma intensive care unit (ICU). PATIENTS: A total of 51 critically ill medical and surgical (including acute trauma) patients who required supplemental oxygen (FIO2 of > or = 0.35) to maintain arterial blood oxyhemoglobin saturation of > or = 90% and who had 62 pulmonary artery catheters placed for patient care reasons. INTERVENTIONS: Pulmonary capillary blood samples were obtained via the pulmonary artery catheters in the "wedged position" at insertion and postinsertion at 8, 24, 48, and 72 hrs. Cytospun smears of the buffy coat aspirates of these samples were made and were stained with Oil Red-O for fat. MEASUREMENTS AND MAIN RESULTS: One investigator, without knowledge of the patients' cardiopulmonary function, examined all smears and graded them 0 to 4+ for amount of fat. Fat scores were correlated with chest radiograph appearance, hemodynamic and respiratory parameters, complete blood cell counts with differential white blood cell counts, whether the patient was receiving lipid-containing parenteral nutrition, principal organ system failure, and reason for ICU admission. Samples from 27 pulmonary artery catheter insertions had no fat, 13 samples had low-grade (1+) episodic fat, and 22 samples had repeated episodes of > or = 2+ fat or isolated episodes of 4+ fat. There was a significant association between the amount of pulmonary microvascular fat and trauma as the reason for ICU admission. Of the other parameters, only chest compliance and body temperature showed unequivocal significant associations. These associations were opposite to the expected findings, but would support a conclusion that fat emboli did not cause the observed cardiopulmonary dysfunction. The inconsistent associations for the FIO2, PCO2, and mixed venous blood oxyhemoglobin saturation may be random events. CONCLUSION: Cardiopulmonary dysfunction commonly attributed to fat emboli is likely due to other causes.

Blood Cell Count↗