Outbreak of aseptic meningitis in Taipei in spring 1993

An outbreak of aseptic meningitis in the Taipei area occurred from January to August 1993. A total of 114 cases were identified by cerebrospinal fluid (CSF) examination at National Taiwan University Hospital. Most of the cases were found from February to May 1993. The peak of age distribution was 3 to 11 years. The male-to-female ratio was 2.1 to 1. Most patients had fever, headache, and vomiting and nausea. On initial CSF examination, protein concentrations > 400 mg/L were noted in 38 of 93 CSF samples, while 19 of 70 initial samples had hypoglycorrhachia (CSF/serum glucose ratio < 0.5). CSF white cell counts of the initial lumbar puncture were 0-9 x 10(6) cells/L in 4 patients, 10-99 x 10(6) cells/L in 42 patients, 100-199 x 10(6) cells/L in 27 patients, 200-499 x 10(6) cells/L in 24 patients, 500-999 x 10(6) cells/L in 12 patients and > or = 1,000 x 10(6) cells/L in 5 patients. Polymorphonuclear cells predominated in 73 of 114 cases. Viral cultures from CSF, throat swabs and rectal swabs were done with a majority yielding enteroviruses. Enterovirus as a definite etiology was found in 58 of 114 cases and was the presumptive etiology in 15 of 114 cases. The serotypes of the enteroviruses isolated were mostly echovirus type 30. All patients recovered without obvious sequelae.

Immunolocalization of thimet oligopeptidase in chicken embryonic fibroblasts

An antiserum was raised against chicken thimet oligopeptidase (TOP), and specific antibodies were isolated by immunoadsorption. The specificity of the antibodies was confirmed by immunoblot analysis with the cell extract of cultured chicken fibroblasts. Subcellular localization of TOP in normal and Rous sarcoma virus-transformed chicken embryonic fibroblasts was investigated by indirect immunofluorescence staining with affinity-purified, monospecific anti-TOP antibodies. In addition to the diffuse reaction expected for a cytosolic enzyme, a punctate, cytoplasmic localization was observed. The appearance of the organelles containing TOP did not correspond to that expected for secondary lysosomes, mitochondria, endoplasmic reticulum, or Golgi apparatus, but did resemble that of endosomes. When cells were allowed to internalize Lucifer yellow before fixation, some of the organelles containing TOP were observed to contain Lucifer yellow. Moreover, those organelles containing TOP were positively immunolabeled with the anti-transferrin receptor antibody. We conclude that part of the TOP in chicken embryonic fibroblasts is located in endosomes and discuss the implications of this.

Magnetic resonance imaging and intraoperative frozen sections in intratemporal facial schwannomas

Seven cases of intratemporal facial schwannoma were assessed by preoperative magnetic resonance imaging (MRI) and intraoperative frozen sections to determine tumor boundaries. These results were then analyzed with respect to gross tumor appearance, under the operating microscope, and final histopathologic diagnosis, with immunostains. Gadolinium-enhanced MRI was helpful in planning the surgical and approach and in defining the extent of tumor involvement relative to the facial nerve. Frozen sections on the other hand were often unreliable in confirming the completeness of resection, frequently overestimating tumor infiltration. Ultimately, tumor-nerve interface, especially in the proximal facial segments, is best judged by its gross intraoperative appearance under high magnification, with the aid of MRI. The difficulty in establishing tumor infiltration in the presence of organized neutral fibers and artifacts is emphasized. Immunohistochemical assays are essential in this regard. Complete tumor removal was achieved in all seven cases, with acceptable functional outcome in those with sufficiently long follow-up.

Abrogation of baboon natural xenoantibody to pig splenocytes by DL-penicillamine

Natural xenoantibodies are believed to be IgM in nature and are known to play a critical role in the hyperacute rejection of distantly related xenografts. The purpose of this study was to determine whether the reducing agent DL-penicillamine could inactivate baboon natural xenoantibodies to pig splenocytes. Pooled baboon serum was treated with varying concentrations of DL-penicillamine over different lengths of time and a complement-mediated cytotoxicity assay was used to determine the reactivity of baboon natural xenoantibodies to pig splenocytes. A whole-cell ELISA assay was used to assess the binding of both IgG and IgM xenoantibodies to pig splenocytes. In addition, DL-penicillamine-treated serum was dialyzed to assess its potential clinical application. These in vitro experiments indicate that both IgM and IgG baboon natural xenoantibodies bind to pig splenocytes, but only IgM xenoantibody is cytotoxic. The binding of baboon natural IgM xenoantibody can be eliminated, and the cytotoxicity of IgM xenoantibody markedly reduced by DL-penicillamine treatment despite continued binding of IgG xenoantibody to pig splenocytes. In addition, DL-penicillamine can be dialyzed, suggesting that it may be an efficacious clinical treatment, the toxicity of which can be regulated with hemodialysis.

Potential of left ventricular assist devices as outpatient therapy while awaiting transplantation

Left ventricular assist devices (LVADs) increasingly are being used as a bridge to transplantation. We studied changes in New York Heart Association class, mean arterial pressure, resting cardiac output, end-organ function, exercise oxygen consumption, and exercise cardiac output in 12 LVAD recipients. In addition, resting levels of neurohormonal factors were evaluated 4 to 16 weeks after implantation. Two of the 12 patients died of right heart failure and 1 of aspiration; all deaths occurred in the first 2 weeks after LVAD implantation. Of the other 9 patients, 8 improved to New York Heart Association class I and 1 to class II, all of whom were in class IV preoperatively. The 4 patients who underwent exercise testing achieved an exercise oxygen consumption of 15.0 +/- 2.7 mL.kg-1.min-1, which was paralleled by an increase in resting cardiac output from 3.07 +/- 0.9 L.min-1 preoperatively to 5.66 +/- 1.1 L.min-1 at 2 months, and mean arterial pressure from 60 +/- 8 to 91 +/- 10 mm Hg at 2 months, a benefit that was maintained for up to 10 months. End-organ function revealed comparable improvement at 2 months for both creatinine (1.68 +/- 0.7 to 1.0 +/- 0.19 mg.dL-1) and total bilirubin (1.37 +/- 1.17 to 0.54 +/- 0.26 mg.dL-1) levels. Levels of neurohormones were within normal limits. Adverse clinical events after the perioperative period were minimal, and no thromboembolic complications occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

TGF beta 1 regulation of collagen metabolism by embryonic palate mesenchymal cells

Proper metabolism of the extracellular matrix (ECM) in mammalian embryonic palatal tissue is required for normal development of the palate. In particular, perturbation of collagen metabolism in the embryonic orofacial region results in the production of cleft palate. Although several types of collagen have been localized in the embryonic palate, factors responsible for regulating their synthesis have not been identified. Transforming growth factor beta (TGF beta), shown to be capable of modulating ECM metabolism in other tissues, has been localized in the developing palate. Thus, we examined the ability of TGF beta 1 to modulate collagen synthesis and degradation in murine embryonic palate mesenchymal (MEPM) cells in vitro. Immunohistochemical analysis confirmed that type III collagen was predominant in the mesenchyme of the embryonic palate, whereas type I collagen was ubiquitous throughout palatal epithelium and mesenchyme. Total collagen production by TGF beta-treated confluent MEPM cells in serum-free conditioned medium was determined by measuring incorporation of L-[2-3-4-5-3H]proline into hydroxyproline. Treatment for 24 hr with TGF beta 1 stimulated incorporation into both cell layer and medium fractions. Quantification of collagen types by ELISA indicated that TGF beta 1 stimulated the accumulation of type III collagen as early as 3 hr after treatment. Northern blot analysis of MEPM cells treated with TGF beta 1 revealed that steady-state levels of mRNA encoding for procollagen alpha 1 (I) and alpha 1 (III) were increased and that these effects were ablated by cycloheximide but not actinomycin. The effects of TGF beta treatment on MEPM cell collagen levels also reflected alterations in collagen degradation. TGF beta-treated MEPM cells exhibited a significant diminution of total protease activity. Moreover, analysis by substrate gel electrophoresis indicated specific decreases in vertebrate collagenase and stromelysin. These data represent the first report of changing proteolytic profiles during palatogenesis. Thus, TGF beta regulates the amount of collagen present in embryonic palatal tissue at the level of synthesis and degradation.

Pyogenic liver abscess in beta-thalassemia major--report of two cases

Pyogenic liver abscess, which may lead to devastating consequences, is an uncommon medical problem in pediatrics and has generally been reported in compromised hosts. This article describes two patients with beta-thalassemia major and hemochromatosis complicated by Klebsiella pneumoniae liver abscess. One of the patients had severe complications, including subphrenic abscess, pleural effusion and meningitis. To present knowledge, the occurrence of K. pneumoniae liver abscess in patients with beta-thalassemia major has never before been reported in the literature.

Improved in vitro models for assay of rheumatoid synoviocyte chemotaxis

OBJECTIVES

(1) To define the optimal conditions for transwell assay of synoviocyte chemotaxis. (2) To develop a live cell imaging chemotaxis assay for synoviocytes. (3) To characterize the chemotaxis of rheumatoid synoviocytes (RAS).

RESULTS

Optimal conditions for transwell assay of synoviocyte chemotaxis were 8 microns pore size filters coated with collagen I (C1), assayed for 24 hours. Without the C1 coating 2.9 x 10(3) RAS migrated to the lower chamber. This increased to 4.7 x 10(3) when 20 micrograms/ml fibronectin (Fn) was added. With the C1 coating 4.3 x 10(3) cells migrated through the filter without chemotactic stimulation compared to 12.8 x 10(3) with interleukin 1 beta (IL-1 beta) 5 ng/ml, 12.2 x 10(3) with granulocyte-macrophage colony stimulating factor (GM-CSF) 25 ng/ml, 11.7 x 10(3) with Fn 20 micrograms/ml, and 9.0 x 10(3) with transforming growth factor-beta 1 (TGF-beta 1) 20 ng/ml (all p < 0.01). In the imaging assay, 50.7% of the RAS migrated toward the C1 coating without bound chemoattract. The percentage of cells migrating toward each chemoattractant at its optimal concentration was 64.3% for IL-1 beta, 60.8% for IL-8, 64.7% for GM-CSF, 61.0% for Fn, 58.9% for IL-6, and 69.1% for TGF-beta 1 (all p < 0.01). All of these chemoattractants increased directed migration without changing the random migration. Indomethacin (100 ng/ml) and Dexamethasone (10 ng/ml) inhibited Fn-induced chemotaxis.

CONCLUSION

We report two in vitro assays for synoviocyte chemotaxis adapted and optimized for the study of synoviocytes. The live cell imaging assay had the advantage that it could separate directed and random migration.

Inversions and deletions generated by a mini-gamma delta (Tn1000) transposon

Intramolecular transposition by an engineered derivative of the transposon gamma delta (Tn1000) is described. This 1-kb element contains inverted repeats of the 40 bp of the delta end of gamma delta, bracketing a kan gene, but it contains no resolution site. Transposition was analyzed in two plasmids; one contained two contraselectable (conditional lethal) genes (thyA and sacB) adjacent to the mini-gamma delta element in a 13.0-kb pBR322/pUC-based two-component plasmid (a heterodimer), and the other contained a different contraselectable gene (strA [rpsL]) in a 13.2-kb three-component plasmid (a heterotrimer). Selection for loss of function of a single contraselectable gene yielded inversions and deletions. Each inversion plasmid was 1 kb larger than the parent plasmid: it had a second copy of mini-gamma delta inserted in the contraselected gene, with that copy plus the intervening segment inverted, and the 5-bp target site duplicated. Each deletion plasmid was smaller than the parent plasmid and had a deletion that extended from one transposon end into or through the contraselected gene for distances of up to 9.4 kb. The frequencies of deletions versus inversions ending in a single target gene were similar, although overall, deletions outnumbered inversions because deletions, but not inversions, into sites beyond the contraselected gene inactivate it. This work also demonstrates that thyA (which encodes thymidylate synthetase) is a useful contraselectable marker.

A mathematical model of sinus node function: validation by recording of sinus node electrograms

We have applied a mathematical function to model sinus node recovery after atrial pacing at different cycle lengths in 13 autonomically denervated, anesthetized canines. This model provides "pure" indexes of sinoatrial conduction and of suppression of automaticity. We compared sinoatrial conduction computed from the model (SACTc) with sinoatrial conduction measured directly utilizing a catheter recording the sinus node electrogram (SACTd) to test the validity of the model. We used both the model and the sinus node electrogram to further define events after pacing. There was close agreement between SACTc and SACTd with correlation coefficients at pacing cycle lengths of 20 and 50% below resting of 0.86 (P < 0.0001) and 0.78 (P < 0.0001), respectively. We verified that the conventional sinus node recovery time is due both to suppression of automaticity and prolongation of sinoatrial conduction. Sinoatrial conduction time returned rapidly to normal over 1-3 beats, whereas automaticity recovered exponentially over 20-40 postpacing intervals. The model accurately describes postpacing phenomena and has the potential to provide a useful adjunct to the measurement of the sinus node electrogram for assessment of sinus node function in the experimental laboratory.

Novel technique for extending the use of allografts in cardiac operations

Small cryopreserved allografts for use in neonates and infants are increasingly difficult to find. We describe a technique for surgically reducing the size of the more readily available large-diameter allografts to make them conform to size requirements appropriate for neonates and infants. This technique involves a longitudinal incision of the allograft from its muscular annulus to its distal orifice with the excision of a single valve leaflet. The two commissural posts of the excised leaflet and the wall of the allograft are then reapproximated with fine suture. Four patients ranging in age from 14 days to 11 months (mean age, 5.2 months) and ranging in weight from 3 to 8.4 kg (mean weight, 5.2 kg) underwent reconstruction of the right ventricular outflow tract using this surgical technique. Two patients underwent repair of truncus arteriosus (age, 14 days and 16 days) and two patients underwent Rastelli operations (age, 9 months and 11 months). The mean follow-up time was 22.5 months (range, 14 to 28 months). All 4 patients are alive and well. One patient requires digoxin and furosemide for moderate quadricuspid truncal valve insufficiency. Serial echocardiography documents mild allograft stenosis in 2 patients and trivial to mild allograft insufficiency in 2 patients. Because handling characteristics and lower bleeding risks render allograft conduits preferable to synthetic conduits and, furthermore, because conduit insertion of any type in the neonate will eventually be outgrown and require replacement, we find this technique to be justifiable as a therapeutic option. In the short term, the technique results in excellent functional results and provides an alternative to synthetic conduits when an appropriate sized allograft is unavailable.

[Effect of ligustrazine on plasma lipid peroxidation, superoxide dismutase of the coronary heart disease]

A clinical study on 59 remote myocardial infarction cases were divided randomly into treated group (31 cases) and normal control group (28 cases). Treated group used intravenously injected Ligustrazine 160 mg a day for 10 days. The plasma lipid peroxidation (LPO), superoxide dismutase (SOD) and sulfhydryl group were measured before and after treatment in the treated group, in comparing with normal control group. The results showed the levels of LPO significantly reduced (P < 0.01), and SOD, sulfhydryl group was obviously increased after Ligustrazine administration (P < 0.05). Attack of angina pectoris was reduced. Between these two group, the difference was significant (P < 0.05). Mechanism of Ligustrazine in reducing LPO and increasing SOD could be the inhibiting of platelet aggregation, regulating the TXA2/PGI2 ratio in plasma, protecting myocardial cell membrane and improving the myocardial ischemia. Ligustrazine could reduce the production of LPO due to the accelerating clearance of oxygen free radical.

Posttransplantation lymphoproliferative disorders treated with cyclophosphamide-doxorubicin-vincristine-prednisone chemotherapy

BACKGROUND

Posttransplantation lymphoproliferative disorders after solid organ transplantation are a serious complication occurring in 1-10% of patients. Different therapies have been used, but the optimal treatment is unknown. There is relatively little information in the literature on the experience with cytotoxic chemotherapy.

METHODS

The disease stage of patients with biopsy-documented posttransplantation lymphoproliferative was determined with standard methods to establish the extent of the disease. Patients in whom the disease failed to regress after initial management, which included reduction in immunosuppression, were treated with a combination chemotherapy regimen consisting of six cycles of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP). Response to therapy was determined by following previously defined sites of disease with appropriate tests. Patients were maintained on a reduced dose of immunosuppressants.

RESULTS

In the four patients studied, lymphoproliferative disorders developed after heart (three cases) or lung (one case) transplantation, which did not regress after immunosuppression was reduced. All four experienced a complete remission with CHOP chemotherapy, which continued at 3, 13+, 20 and 30+ months after completion of treatment. One patient died of sepsis after completing therapy at a point when his leukocyte count was normal, and no evidence of posttransplantation lymphoproliferative disorder was found at autopsy. A second patient died of liver failure with no clinical evidence of lymphoproliferative disorder.

CONCLUSION

Although this is a small series, it demonstrates that patients with posttransplantation lymphoproliferative disorders may respond to cytotoxic chemotherapy. The duration of response is undetermined.

[Specific curative effects of nitrosourea drugs on tumor cells with Mer--phenotype in Chinese]

O6-Methylguanine DNA methyltransferase (O6-MT) activity and cellular sensitivity to nitrosourea drugs of 10 kinds of tumor cell strains derived from Chinese patients were measured by 3H radioactivity and colony-forming ability, respectively. The results in vitro showed that nimustine (Nim) 25 micrograms.ml-1 and carmustine (Car) 20 micrograms.ml-1 exhibited specific killing effects on Mer-phenotype tumor cells characterized by low O6-MT activity. In vivo both Nim and Car (25 mg.kg-1.wk-1 x 4 wk, ip) had specific curative ability to Mer- tumor cells implanted in nude mice. These findings suggested that assay of O6- MT activity in tumor biopsy could be used as a predictable guide to human tumor chemotherapy with nitrosourea compounds.

Fungal esophagitis in children

Seven patients were endoscopically diagnosed as having a fungal esophagitis with mycologic or histologic support for the diagnosis from 1979 to 1991 in the Department of Pediatrics, National Taiwan University Hospital. The major causative agent was Candida albicans. Other fungi isolated were Candida Krusei, Trichosporon cutaneum, Trichosporon beigelii, and Rhodotorula rubra, but they all resembled one another under endoscopic examination. The most common presenting symptom was hematemesis, and the lower part of the esophagus was more often involved. Only one patient was documented to have oral thrush. Most of the children did not present typical symptoms of esophagitis such as dysphagia or odynophagia, and they tended to be in more advanced stages of the disease when the diagnosis was made.

Importance of electrode design, lead configuration and impedance for successful low energy transcatheter atrial defibrillation in dogs

OBJECTIVES

We assessed the feasibility of low energy endocardial defibrillation in a canine model of atrial fibrillation, comparing catheters with large surface area electrodes and standard electrode catheters, and evaluated the effects of lead configuration and circuit impedance on defibrillation energy requirements.

BACKGROUND

Although recent animal studies have demonstrated the feasibility of low energy endocardial atrial defibrillation, their results have been conflicting with regard to important methodologic aspects.

METHODS

In 14 anesthetized greyhounds, atrial fibrillation was induced by rapid atrial pacing and maintained by vagal stimulation. Two large surface area braided electrode catheters and two standard electrode catheters were introduced percutaneously, one of each, in the right atrial appendage and right ventricular apex. A cutaneous patch electrode was placed on the left thorax. Biphasic shocks synchronized to the ventricular electrogram were used to terminate atrial fibrillation. Seven configurations were evaluated. Three used standard electrodes: proximal atrial cathode to distal atrial, ventricular or cutaneous anode. Four used braided electrodes: three with atrial cathode to ventricular, cutaneous or combined anode; one with ventricular cathode to atrial anode.

RESULTS

Defibrillation with standard electrode catheters was associated with high impedance (576 +/- 112 omega) and low success rates for all configurations (28% success at < or = 40 J, no successes at 10 J). Low energy defibrillation was readily achieved with the braided electrodes with significantly lower impedance (75 +/- 13 omega, p < 0.0001). Ventricular fibrillation did not occur. The success rate of cardioversion increased in a dose-response manner, allowing fitting of a sigmoid curve and calculation of energy associated with 50% (ED50) and 90% (ED90) success. The most successful configuration was ventricular cathode/atrial anode (ED50 1.5 +/- 0.4 J), and the least successful was atrial anode/cutaneous patch (ED50 6.5 +/- 3.2 J, p = 0.0001).

CONCLUSIONS

Low energy atrial defibrillation is feasible using large surface area electrodes but not with standard electrode catheters owing to high impedance. An intracardiac anode provides lower impedance and higher success rates than are provided by a cutaneous anode.

Clinical experience with cardiac retransplantation

Although more than 560 patients worldwide have undergone cardiac retransplantation, few studies of this population have been reported. To evaluate the risk of cardiac retransplantation and to better establish selection criteria, we reviewed the records of all patients who underwent retransplantation at the Columbia-Presbyterian Medical Center. Of 431 patients who underwent transplantation between February 1977 and March 1991, 408 underwent the procedure in the era of cyclosporine-based immunosuppression. Thirteen of these 408 patients underwent retransplantation (including one patient who received a third graft). Indications for the 14 retransplantations included transplant coronary artery disease (n = 8), rejection (n = 5), and intraoperative graft failure (n = 1). Immunosuppression and follow-up protocols used in this cohort were similar to those in the primary transplantation population. No significant differences were found in either actuarial survival between primary transplant recipients (75.1% +/- 2.2% at 1 year and 71.3% +/- 2.4% at 2 years) and patients who underwent retransplantation (71.4% +/- 12.1% at 1 year and 59.5% +/- 14.8% at 2 years) or in linearized rates of rejection and actuarial freedom from rejection between the two groups. No differences between these groups were found with regard to age, sex, race, origin of end-stage heart disease, or early (< 30 day) mortality. The origin of primary graft failure did not correlate with survival outcome in the retransplantation cohort. Follow-up time for patients having primary transplantation ranged from 0 to 8 years (mean 24 months) with a cumulative patient follow-up of 830 patient-years; follow-up time for patients who underwent retransplantation ranged from 0 to 3 years (mean 8.1 months) with a cumulative patient follow-up of 9.5 patient-years. Approximately 50% of patients in both groups had at least one rejection episode by 3 months. Within the limited time period studied after retransplantation, only one patient had transplant coronary artery disease, approximately 27 months after her first retransplantation procedure for acute rejection. These results indicate that the prognosis for patients undergoing cardiac retransplantation is good for patients for whom the indication for retransplantation is identified more than 30 days after initial transplantation.

The transotic approach in acoustic neuroma surgery

A consecutive series of 147 transotic operations for the removal of acoustic neuroma is presented. The advantages of this approach over the conventional translabyrinthine technique are several, including 1) a wider surgical access with a circumferential exposure of the internal acoustic meatus and the porus acousticus; 2) the direct visualization and access to the anterior cerebellopontine angle where the facial nerve is usually tenuous and most vulnerable; and 3) the permanent closure of the ear canal and eustachian tube with complete obliteration of the surgical cavity, minimizing cerebrospinal fluid leaks. These advantages have translated into improved surgical outcomes. In our series of 147 patients spanning 11 years, total tumor extirpation was achieved in all patients, with one mortality, three CSF leaks, and one meningitis. The facial nerve was anatomically preserved in 95% of the cases. This approach is capable of attaining the widest, and the most direct access to the cerebellopontine angle without cerebellar retraction.

Management of lymphoproliferative disorders after cardiac transplantation

We conducted a retrospective study of 516 cardiac recipients who underwent transplantation between April 1983 and April 1992, 19 of whom had development of post-transplantation lymphoproliferative disorders (PTLDs). These 19 patients presented with involvement of lung (5), gastrointestinal tract (5), disseminated disease (6), and adenoids and lymph nodes (3). B-cell proliferations ranging from an atypical hyperplasia to malignant lymphoma developed in 18 patients, and mixed cellularity Hodgkin's disease developed in 1 patient. The 19 patients with PTLD displayed a predominance of both women and cardiomyopathy as the indication for transplantation when compared with two separate control populations. No correlation was found between demographic criteria analyzed and (1) early versus late diagnosis of PTLD after transplantation, (2) the site of PTLD involvement, or (3) the histopathologic category of the PTLD lesion. Patients with gastrointestinal tract and lung PTLD involvement enjoyed an improved survival after both transplantation and PTLD diagnosis when compared with patients with PTLD involvement of all other extranodal sites. We report a high incidence of PTLD involving the lung and gastrointestinal tract in our cohort study. These sites of involvement responded better to a reduction in immunosuppression than did the other extranodal sites of involvement.

Radiofrequency catheter ablation of tachyarrhythmias--adult and paediatric experience

BACKGROUND AND AIMS

Until recently, curative therapy for supraventricular tachycardia (SVT) was possible only with map-guided cardiac surgery. The ability to ablate permanently the reentrant circuit responsible for tachycardia using radiofrequency electrical current (RF) delivered through a catheter has now allowed cure of SVT by non-surgical means. We present our initial experience with this technique in both adult and paediatric patients.

METHODS

In 53 patients of median age 32 years, 56 radiofrequency catheter ablation procedures were performed for control of tachyarrhythmias. Fourteen patients were aged 18 years or less. Indications for RF ablation were SVT due to an accessory pathway (n = 27), SVT due to atrioventricular junctional reentry (AVJRT) (n = 22), incessant SVT (n = 2), ventricular tachycardia (n = 2), and uncontrolled atrial fibrillation (n = 3). General anaesthesia was used in 88% of procedures. Ablation was preceded by electrophysiological testing to confirm tachycardia mechanism in all cases.

RESULTS

The ablation procedure was completely successful in 49/56 cases (87.5%) and partially successful in another two cases. Only five procedures (9%) failed. Median procedure time was two hours, median fluoroscopy time was 24 min, and the median number of RF applications was four. There were no major differences in results comparing adult and paediatric patients. A transient ulnar nerve palsy was the only major complication observed. After a follow-up of one to 15 months, tachycardia has recurred in two patients (4%). Of the total 53 patients, 90.5% are currently asymptomatic and off all cardiac drug therapy. RF catheter ablation appears to be an effective, curative, and relatively safe alternative to long term drug therapy in the management of troublesome SVT.

Structure-function correlations of calcium binding and calcium channel activities based on 3-dimensional models of human annexins I, II, III, V and VII

The annexins are a family of calcium-dependent phospholipid-binding proteins which share a high degree of primary sequence similarity. Using a model of the crystal structure of annexin V as a template, 3-dimensional models of human annexins I, II, III and VII were constructed by homology modeling (J. Greer, J. Mol. Biol. 153, 1027-1042, 1981; J.M. Chen, G. Lee, R.B. Murphy, R.P. Carty, P.W. Brant-Rauf, E. Friedman and M.R. Pincus, J. Biomolec. Str. Dyn. 6, 859-87, 1989) for the 316 amino acid portions corresponding to the annexin V structure published by Huber et al. (J. Mol. Biol. 223, 683-704, 1992). These methods were used to study structure-function correlations for calcium ion binding and calcium channel activity. Published experimental data are specifically shown to be consistent with the annexin models. Possible intramolecular disulfide bridges were identified in annexin I (between Cys297 and Cys316) and in annexins II and VII (between Cys115 and Cys243). Each of the annexin models have 3 postulated calcium binding sites, usually via a Gly-Xxx-Gly-Thr loop with an acidic Glu or Asp residue 42 positions C-terminal to the first Gly. Despite a nonconserved binding site sequence, annexins I and II are able to coordinate calcium in domain 3 since the residue in the second loop position is directed toward the solvent away from the binding pocket. This finding also suggests a mechanism for a conformational change upon binding calcium. Highly conserved Arg and acidic sidechains stabilize the channel pore structure; annexin channels probably exist in a closed state normally. Arg271 may be involved in channel opening upon activation: basic residue 254 can stabilize Glu112, which allows Arg271 to interact with residue 95 instead of Glu112. Residue 267, found on the convex surface at the pore opening, may also be important in modifying channel activity.

Modulation of O6-methylguanine-DNA methyltransferase-mediated 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea resistance by O6-benzylguanine in vitro and in vivo

Our previous studies have indicated that O6-methyl-guanine-DNA methyltransferase (MGMT) is a key factor determining tumor cellular resistance to 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea (ACNU). This study describes the modulation of MGMT-mediated ACNU resistance by O6-benzylguanine pretreatment. The ACNU sensitivity of MGMT proficient human tumor HeLa S3, SMMC-7721, and Cc801 cells in tissue culture was markly enhanced by 10 mm O6-benzylguanine, and a correlation between the extent of enhancement and the level of MGMT activities was observed. A single i.p. injection of 100 mg/kg of O6-benzylguanine caused a complete inhibition of MGMT activities in HeLa S3 tumor xenografts and combination of O6-benzylguanine with ACNU (7.5 mg/kg) significantly inhibited HeLa S3 tumor growth. The results demonstrated that O6-benzylguanine could be used as a potential adjuvant in combination chemotherapy with ACNU to treat MGMT proficient tumors.

Depletion of O6-methylguanine-DNA methyltransferase and potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea antitumor activity by O6-benzylguanine in vitro

The overcoming effect of O6-benzylguanine on O6-methylguanine-DNA methyltransferase (MGMT)-mediated 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) resistance in vitro was evaluated. Depletion of MGMT activity in Mer+ HeLa S3 cells by O6-benzylguanine was dose-dependent and a complete loss of MGMT activity was achieved at a concentration of 0.5 microM. The cytotoxic potential of BCNU on MGMT proficient HeLa S3 (1.10 pmol/mg of protein), SMMC-7721 (0.72 pmol/mg of protein) and Cc801 (0.39 pmol/mg of protein) was greatly enhanced when cells were exposed to 10 microM O6-benzylguanine for 1 h, but there was a lack of potentiation of BCNU sensitivity in Mer- HeLa MR cells due to its nearly undetectable level of MGMT. There existed a correlation between the extent of enhancement and the amount of MGMT activity. The intensity of enhancement expressed as dose modifying factor = IC50 (BCNU alone)/IC50 (10 microM O6-benzylguanine + BCNU) was 4.56, 3.89, 3.67 and 0.97 in HeLa S3, SMMC-7721, Cc801 and HeLa MR cells respectively. The results further demonstrated that O6-benzylguanine may have potential utility as an adjuvant in combination chemotherapy with chloroethylnitrosourea agents.

[Effects of atropine on contraction of rabbit aortic smooth muscle and cell proliferation]

The calcium antagonistic actions of atropine (Atr) and verapamil (Ver) were studied on the contraction of rabbit thoracic aorta strips induced by CaCl2 and KCl. Both Atr and Ver were found to depress the contraction as demonstrated by the shift-to-right of the dose-effect relationship curves and the decrease of maximal responses, with the value of pD'2 being 4.4 and 5.8 respectively. The intracellular Ca(2+)-dependent component of NE-induced aortic strip contraction was also inhibited by the 2 drugs, but the extracellular Ca(2+)-dependent component was barely or not inhibited by Atr before its concentration was raised to 100 mumol/L. These results indicate that the depressive effect of Atr on aortic contraction is mainly exerted by acting on the PDC (potential-dependent channel). The action of Atr on proliferation of cells was also studied in rabbit aortic smooth muscle cell (ASMC) culture. The growth was inhibited by Atr when Ca2+ was present in the medium. When Ca2+ was absent, however, the growth was stimulated by Atr 20.6-185.2 mumol/L, but inhibited by Atr 555.7-1666.7 mumol/L, suggesting that Ca2+ is somehow involved in the action of Atr on ASMC growth.

Enkephalin is a competitive antagonist of cholecystokinin in the gastrointestinal tract, as predicted from prior conformational analysis

Prior calculations based on ECEPP (Empirical Conformational Energies for Peptides Program) of the low energy minima for cholecystokinin (CCK) and Met-enkephalin have demonstrated that significant structural features of these two peptides are identical. This result suggested the possibility that Met-enkephalin, as well as other enkephalin analogues of similar structure, could associate with receptors for CCK. To test this theoretical result, we examined the ability of Met-enkephalin and its analogues to bind to peripheral CCK receptors in the rat gastrointestinal tract; in particular, we measured the ability of the opiate peptide to inhibit the effects of CCK in a physiological assay system which we have previously characterized: CCK-induced contraction of the isolated rat pyloric sphincter. We find that Met-enkephalin is an antagonist of the CCK-8-induced contraction, with a IC50 of 110 nM. Furthermore, antibodies against CCK were found to cross-react with Met-enkephalin and its analogues in a manner which suggests a distinct structure-activity relationship. These experimental results strongly support the theoretical results of conformational analysis showing structural similarity between enkephalin and CCK. They further suggest that enkephalins could modulate the response of CCK systems under physiological conditions.

Primary structure of an inactive mutant of phospholipase A2 in the venom of Bungarus fasciatus (banded krait)

From the acidic components of Bungarus fasciatus venom, a very small amount (0.16%) of a novel phospholipase A2 was obtained. Both neurotoxicity and enzyme activity were found to be lacking. Amino acid sequence study showed that it has a normal backbone of group I snake venom phospholipase A2 with 118 amino acid residues. The lack of enzyme activity was attributed to its mutation of the indispensable Asp residue to an Ala residue, i.e., the usual His-Asp47 turned out to be His-Ala47. This is the eighth isoform of phospholipase A2 found from the venom of Bungarus fasciatus. Examination of structural homology with three other isoforms revealed 66% similarity at most.

O6-methylguanine-DNA methyltransferase activity in human tumors

The distribution of O6-methylguanine-DNA methyltransferase (MGMT) activity in extracts of tumors from 74 patients was measured. The results demonstrated that there was considerable variation of MGMT activity in different human tumor tissues as well as in different individuals. The mean values (X +/- SD, pmol/mg of protein) in breast cancer, stomach cancer, small cell lung cancer, non-small cell lung cancer, renal cell carcinoma, esophageal carcinoma, brain tumors, colon carcinoma and malignant melanoma were 1.071 +/- 0.374 (9), 0.515 +/- 0.107 (5), 0.509 +/- 0.251 (5), 0.461 +/- 0.227 (24), 0.329 +/- 0.246 (5), 0.273 +/- 0.376 (5), 0.244 +/- 0.175 (14), 0.242 +/- 0.308 (5) and 0.201 +/- 0.161 (2) respectively. It was notable that six samples (1/24 non-small cell lung cancer, 3/5 esophageal carcinoma, 1/14 brain tumors and 1/5 colon carcinoma) did not have any detectable level of MGMT activity. Activity of glutamine pyruvic transaminase (GPT) was also measured in the same extracts used for the assay of MGMT activity. The activity of GPT in these samples with undetectable level of MGMT activity was similar to those with significant MGMT activity. These results further strengthen the assumption that a certain fraction of human tumors are Mer-.

Early surgical intervention for orbital floor fractures: a clinical evaluation of lyophilized dura and cartilage reconstruction

Experience in the management of 77 isolated orbital floor fractures is presented. The transconjunctival approach was used exclusively to access the orbital floor and lyophilized dura and cartilage were used to reconstruct the floor, when indicated. Follow-up for an average of 36 months showed excellent cosmetic and functional results. A 20% complication rate was noted, which compares favorably with what is reported in the literature. There were no graft extrusions or infections and only one case of graft displacement. These findings support the concept of early treatment of orbital floor fractures, even in "minimally symptomatic" patients. Lyophilized dura and cartilage proved to be safe and effective materials for orbital reconstruction.

[Calcium antagonism of anisodamine on isolated rabbit thoracic aorta]

Anisodamine (Ani) or verapamil (Ver) relaxed the contracted thoracic aortic strips induced by CaCl2 and KCl in a noncompetitive manner with pD2' 3.6 and 5.8, respectively. Ani 50 mumol.L-1 and Ver 1 mumol.L-1 inhibited the intracellular Ca(2+)-dependent component of norepinephrine-induced contraction of aorta, but Ani 0.1 mmol.L-1 did not decrease the extracellular Ca(2+)-dependent component. In the presence of Ca2+, Ani 2.3 mumol.L-1 inhibited the proliferation of aortic smooth muscle cells. In the absence of Ca2+, the effect induced by Ani was biphasic-stimulatory at 2.3 mumol.L-1 concentrations and inhibitory at 61.7 mumol.L-1 concentrations. These results suggest that Ani, similar to Ver, mainly inhibits the potentially operated calcium channels.

Chronic recurrent multifocal osteomyelitis: report of a case

We report on a Chinese boy with chronic recurrent multifocal osteomyelitis (CRMO). The eight-year-old boy presented with intermittent exacerbation and spontaneous remission of bone pain at two bone sites, associated with local erythema, swelling and tenderness. The white blood cell count, erythrocyte sedimentation rate, alkaline phosphatase, lactate dehydrogenase, calcium and phosphate were normal or mildly elevated. The roentgenogram and scintigram were consistent with osteomyelitis. The pathologic feature of the bone biopsy specimens was compatible with osteomyelitis. However, no organisms were consistently isolated from culture, and the disease was unaffected by antimicrobial therapy. CRMO is an uncommon childhood disease of still unknown etiology. It is the purpose of this paper to present our experience with the first case in a Chinese person and to review the literature with a discussion of what is currently known about CRMO.

Meningitis caused by human herpesvirus-6

Since the discovery of human herpesvirus-6 (HHV-6) the illnesses associated with it have increased steadily. Two infants with meningitis are reported: both suffered a mild meningitis and serological studies confirmed an acute HHV-6 infection. This report supports a role of HHV-6 in nervous system disease.

Extensive upper aerodigestive tract anomalies in 'VACTERL' Association

Extensive upper aerodigestive tract anomalies are rare in newborns. When they occur, they are often accompanied by other congenital malformations. We present a case of a newborn who presented to the Montreal (Quebec) Children's Hospital with severe tracheoesophageal abnormalities, as part of vertebral, anal, cardiac, tracheal, esophageal, renal, and limb anomalies (VACTERL) association. In spite of surgical intervention, the patient finally succumbed to other congenital abnormalities. Management of infants with such conditions usually involve complex reconstructive efforts, while prognoses remain poor due to other congenital defects and cardiopulmonary complications.

An energetic evaluation of a "Smith" collagen microfibril model

An energy minimized three-dimensional structure of a collagen microfibril template was constructed based on the five-stranded model of Smith (1968), using molecular modeling methods and Kollman force fields (Weiner and Kollman, 1981). For this model, individual molecules were constructed with three identical polypeptide chains [Gly-Pro-Pro)n, (Gly-Prop-Hyp)n, or (Gly-Ala-Ala)n, where n = 4, 12, and 16) coiled into a right-handed triple-helical structure. The axial distance between adjacent amino acid residues is about 0.29 nm per polypeptide chain, and the pitch of each chain is approximately 3.3 residues. The microfibril model consists of five parallel triple helices packed so that a left-handed superhelical twist exists. The structural characteristics of the computed microfibril are consistent with those obtained for collagen by X-ray diffraction and electron microscopy. The energy minimized Smith microfibril model for (Gly-Pro-Pro)12 has an axial length of about 10.2 nm (for a 36 amino acid residue chain), which gives an estimated D-spacing (234 amino acids per chain) of approximately 66.2 nm. Studies of the microfibril models (Gly-Pro-Pro)12, (Gly-Pro-Hyp)12, and (Gly-Ala-Ala)12 show that nonbonded van der Waals interactions are important for microfibril formation, while electrostatic interactions contribute to the stability of the microfibril structure and determine the specificity by which collagen molecules pack within the microfibril.

Roseola infantum caused by human herpesvirus-6: report of 7 cases with emphasis on complications

Roseola infantum is not an uncommon disease in children. The etiology was not known until 1988 when Yamanishi et al in Japan first demonstrated that human herpesvirus-6 (HHV-6) was the causative agent. In the fall of 1989, we began to study the role of HHV-6 in roseola infantum in Taiwan. A total of 7 cases of suspected roseola infantum were studied and all were proven to have primary HHV-6 infections. Six were classic cases of roseola infantum, while one had only fever without the rash. Two cases developed complications; one had leukopenia and thrombocytopenia and the other had aseptic meningitis and mononucleosis. This is the first report to substantiate that HHV-6 is an important cause of roseola infantum in Taiwan, and that the virus could cause meningitis and thrombocytopenia.

Efficacy and safety of oral cefixime therapy in common infectious diseases in children

Twenty-nine children, including 20 boys and 9 girls, were enrolled in an open trial of oral cefixime therapy for common pediatric infectious diseases. Patients aged between 0.5 month and 12 years with a mean +/- standard deviation of 2.3 +/- 2.8 years. The diagnoses included 10 of acute otitis media, 2 of purulent rhinitis, 4 of acute enterocolitis, and 13 of urinary tract infection. Most children received 6-12 mg/kg/day of cefixime granules, orally twice daily for more than five days. All 10 cases (100%) of acute otitis media and 2 cases of purulent rhinitis were either cured, or improved by oral cefixime treatment. None of them was microbiologically evaluable. Four cases (100%) of acute enterocolitis, 3 due to Salmonella group B, one due to Shigella flexneri, were also successfully treated with bacteria eradication. However, the cure rate of 13 cases of urinary tract infection was only 85% (11/13). Seven Escherichia coli and 4 Proteus mirabilis infections were eradicated, whereas one each of Enterobacter cloacae and Klebsiella pneumoniae infections did not respond to treatment; these two cases had a complicated course. The overall cure and improvement rate was 93%. Although five patients had transient episodes of mild diarrhea, no significant adverse reaction was observed. In summary, oral cefixime given twice daily was effective and safe in the treatment of a variety of common infectious diseases in pediatric patients.

The amino acid sequence and properties of an edema-inducing Lys-49 phospholipase A2 homolog from the venom of Trimeresurus mucrosquamatus

Three phospholipase A2 enzymes or homologs were purified from the venom of Trimeresurus mucrosquamatus (Taiwan habu). The most abundant one was found to be a phospholipase homolog without enzyme activity, and its complete amino acid sequence was determined using oligopeptide fragments derived from digestion by endopeptidases Glu-C, Asp-N, Lys-C and alpha-chymotrypsin, and by means of gas-phase sequencing. The sequence revealed that the protein belonged to the Lys-49 family of snake venom phospholipase A2. This protein's function was characterized as edema-inducing. The Lys-49 protein has the potential to bind membrane phospholipid and Ca2+ (Kd = 1.6 x 10(-4) M) as shown by ultraviolet difference spectra; however, the catalytic site appeared to be inactive and the edematous response was independent of the protein's hydrolytic activity. Mast cells and platelets were shown to be subject to activation by the Lys-49 protein.

Isolation and characterization of a 70-kDa metalloprotease (gelatinase) that is elevated in Rous sarcoma virus-transformed chicken embryo fibroblasts

Chicken embryo fibroblasts (CEF) transformed by Rous sarcoma virus (RSVCEF) secrete a 70-kDa metallo-gelatinase at elevated levels over that of normal CEF. The 70-kDa enzyme has been purified from RSVCEF conditioned medium and represents 1-3% of the total protein in the RSVCEF conditioned medium. A 22-kDa protein, which appears to be the avian form of the tissue inhibitor of metalloproteases (TIMP), is co-isolated in association with the 70-kDa enzyme and can be separated from the enzyme by gel filtration carried out under denaturing conditions. The isolated 70-kDa species is in the zymogen form. It can be activated by treatment with the organomercurial, p-aminophenylmercuric acetate (APMA), yielding a 62-kDa active species derived by an apparent autoproteolytic cleavage from the 70-kDa proenzyme as determined by both substrate gel analysis and immunoblots using a monospecific antibody to the 70-kDa proenzyme. The proenzyme is poorly activated by trypsin and not activated by plasmin. The APMA-activated enzyme rapidly degrades denatured collagens but under identical conditions is unable to degrade native collagens, including basement membrane type IV collagen. Only at very high enzyme to substrate ratios (1:2) will native type IV collagen be hydrolyzed. Partial N-terminal amino acid sequencing of both the 70-kDa proenzyme and the 62-kDa active enzyme indicates that the avian enzyme is a member of the matrix metalloprotease family (MMP-2). When CEF cultures, infected with a temperature sensitive mutant of RSV, conditional for the expression of the transforming src oncogene, were incubated at the permissive and nonpermissive temperatures, differential levels of the 70-kDa enzyme were produced in direct proportion to the functioning of the src oncogene.

The proto-oncogene c-ros codes for a transmembrane tyrosine protein kinase sharing sequence and structural homology with sevenless protein of Drosophila melanogaster

Our earlier study predicted that proto-oncogene c-ros codes for a receptor-like tyrosine protein kinase (TPK). To further understand its protein structure and physiological function, we have analysed its expression in various tissues of chicken and have isolated and sequenced cDNA clones containing the entire coding region of the gene. Confirming our earlier study, we found that kidney is the organ that expresses the highest level of c-ros mRNA, in addition, we found a lower level of expression in gonad, thymus, bursa and brain. A distinctive 8.3 kb c-ros mRNA is present in kidney. No detectable amount of c-ros mRNA was found in the rest of tissues examined. Nucleotide sequence of the c-ros cDNA predicts that it codes for a transmembrane (TM) TPK molecule of 2311 amino acids (aa). The extracellular domain consists of 1873 amino acids which share 20 to 43% homology with that of the Drosophila sevenless protein and TPK domains of the two genes have 58 to 74% homology. The extracellular domain containing 37 potential N-linked glycosylation sites is preceded by a 5' hydrophobic sequence resembling a typical signal peptide. An internal hydrophobic domain of 26 amino acids, the presumed transmembrane domain, is followed by a spacer sequence of 58 amino acids, a TPK domain of 270 amino acids and a carboxyl tail of 84 amino acids. Overall, our result indicates that c-ros codes for a glycosylated transmembrane TPK molecule which shares a remarkable sequence and structural homology with that of Drosophila sevenless protein.

[Granule protein contents of polymorphonuclear leucocytes and serum in 30 cases of myelodysplastic syndromes]

Intracellular contents and serum levels of neutrophilic granule protein components, including myeloperoxidase (MPO), lactoferrin (LF) and lysozyme (LYZ), were investigated in 30 cases of myelodysplastic syndromes (MDS), with 59 healthy adult donors as controls. Both neutrophilic MPO and LF decreased significantly, suggesting the transformation of abnormal clones. Both serum levels of LF and LYZ exhibited a considerable fluctuation which may reflect reflect granulopoiesis in the bone marrow. We are of the opinion that measurement of intracellular MPO, LF, LYZ and their serum levels may aid in the diagnosis and prognosis of MDS and is proved to be of great clinical significance.

Significance of pre-S2 protein and its antibody in children with HBV infections

Pre-S2 protein and its antibody were detected in 130 children with hepatitis B virus (HBV) infection and 30 with T6 hepatitis B (HB) vaccination. The results showed that pre-S2 was positive in most chronic persistent hepatitis (CPH) and chronic active hepatitis(CAH) patients, while anti-pre-S2 was positive in only 8% (2/92 cases) and 11.5% (3/26 cases) respectively. The positive rate of anti-pre-S2 was 78.9% (15/19 cases) in cases at the convalescent stage of acute hepatitis B, 91.7% (55/60 cases) in cases with T6 HB vaccination and 83.3% (25.30 cases) in naturally acquired anti-HBs children, while pre-S2 was not noted. Anti-pre-S2 was negatively related to ALT and positively to anti-HBs (P less than 0.01). The positive relation of pre-S2 to HBsAg was observed. These results suggest that pre-S2 could be a marker for HBV infection, and anti-pre-S2 may indicate a favourable prognosis of HBV infection. There was no correlation between anti-pre-S2 and pathogenic damages induced by HBV.

Serine protease and metallo protease cascade systems involved in pericellular proteolysis

Cultures of transformed fibroblasts actively involved in extracellular matrix degradation have been examined for initial activation of serine and metallo protease cascade systems. Rous sarcoma virus transformed chick embryo fibroblasts (RSVCEF), in contrast to transformed mammalian cells, produce active, two chain urokinase-type plasminogen activator (tcu-PA). Active tcu-PA is found in serum-free, plasmin-free conditioned medium from RSVCEF cultures as determined by two independent methods, immunoprecipitation and differential DFP sensitivity. RSVCEF cultures synthesize and secrete inactive, single chain uPA (scu-PA) which is converted to tcu-PA in a time dependent manner by a catalytic mechanism that appears to involve a functioning uPA receptor on the surface of intact cells. The enzyme activity responsible for this conversion may represent the initiating catalytic event in the PA/plasminogen serine protease cascade system. A 70 kDa prometalloprotease capable of degrading denatured collagen following its activation also is significantly elevated in RSVCEF cultures over that of normal CEF. Trace amounts of the active 62 kDa form of the metalloprotease (gelatinase) is found in the transformed RSVCEF cultures indicating that these cultures produce a natural activator of the prometalloprotease. Plasmin and/or PA do not appear to be the activator of this enzyme as determined by indirect inhibition assays and direct assays employing purified enzymes. The possible central position of pro PA and the 70 kDa prometalloprotease in an interacting, complex protease cascade system involved in extracellular matrix degradation is discussed.

Comparison of the predicted structure for the activated form of the P21 protein with the X-ray crystal structure

The predicted conformation and position of the central transforming region (residues 55-67) of the p21 protein are compared with the conformation and position of this segment in a recently determined X-ray crystal structure of residues 1-166 of this protein in the activated state bound to a nonhydrolyzable GTP derivative. We previously predicted that this segment of the protein would adopt a roughly extended conformation from Ile 55-Thr 58, a reverse turn at Ala 59-Gln 61, followed by an alpha-helix from Glu 62-Met 67. We further predicted that this region of the activated protein occupies a position that is virtually identical to corresponding regions in the homologous purine nucleotide-binding proteins, bacterial elongation factor (EF-tu), and adenylate kinase (ADK). We find that there is a close correspondence between the conformation and position of our predicted structure and those found in the X-ray crystal structure. A mechanism for activation of the protein is proposed and is corroborated by X-ray crystallographic data.

Conformations of the central transforming region (Ile 55-Met 67) of the p21 protein and their relationship to activation of the protein

The GTP-binding p21 protein, encoded by the ras-oncogene, becomes transforming if amino acid substitutions are made at critical positions in the polypeptide chain, e.g., at Gly 12, Gly 13, Ala 59, Gln 61 and Glu 63. Most of these substitutions occur in two phosphate-binding loop regions, Tyr 4-Thr 20, herein designated as segment 1, and Ile 55-Met 67, herein designated, as segment 2. These two segments are homologous to two corresponding regions in the two purine nucleotide binding proteins, bacterial elongation factor (EF-tu) (Val 12-Thr 28 corresponds to segment 1; His 78-Ile 92 corresponds to segment 2) and adenylate kinase (ADK) (Lys 9-Cys 25 corresponds to segment 1 and Tyr 95-Arg 107 corresponds to segment 2). We find that the conformations of the segment 1 region in the p21 protein, EF-tu and ADK are similar to one another and that the conformation of the segment 2 region of EF-tu is superimposable on that of segment 2 of ADK. Furthermore, the relative position of the two segments in EF-tu is strikingly similar to that of the two segments in ADK. In the originally proposed X-ray structure for the p21 protein, the conformation of segment 2 in the p21 protein is not similar to that found for the other two proteins, and its disposition relative to segment 1 and the remainder of the protein is also different from that observed for the other two proteins.(ABSTRACT TRUNCATED AT 250 WORDS)