Catabolic ornithine carbamoyltransferase of Pseudomonas aeruginosa. Changes of allosteric properties resulting from modifications at the C-terminus

Ornithine carbamoyltransferases (OTCases) catalyse the formation of citrulline and phosphate from ornithine and carbamoylphosphate by a thermodynamically favoured reaction. In vivo, catabolic OTCase of Pseudomonas aeruginosa promotes the reverse reaction, the phosphorolysis of citrulline. Although the enzyme is assayed in vitro in the direction of citrulline synthesis, the enzyme cannot perform this reaction in vivo due to poor affinity for carbamoylphosphate and high cooperativity towards this substrate. Furthermore, the dodecameric catabolic OTCase is an allosteric enzyme; the enzyme is stimulated by nucleoside monophosphates and inhibited by polyamines (e.g. spermidine). A previous study showed that a modification of the C-terminus of the catabolic OTCase alters the homotropic cooperativity of the enzyme. We have now investigated the importance of the C-terminus for homotropic and heterotropic cooperativity by site-directed mutagenesis. Deletion of the C-terminal Ile335 residue strongly reduced cooperativity for carbamoylphosphate and sensitivity to spermidine. These properties were essentially restored when the two C-terminal amino acids (Asp334 and Ile335) were removed by deletion. However, in this variant enzyme, AMP failed to abolish carbamoylphosphate cooperativity completely, whereas the wild-type enzyme was rendered virtually non-cooperative by AMP. An extension of catabolic ornithine carbamoyltransferase by 15 amino acid residues interfered with both homotropic and heterotropic interactions and lowered the maximal velocity. All variant enzymes had the same dodecameric structure as the wild type and differed only slightly in affinity for the second substrate ornithine. A structural model of the dodecamer, at 0.3-nm resolution, suggests that the C-terminus could be involved in trimer/trimer interaction. We propose that modifications at the C-terminus alter the trimer/trimer interface and, in addition, removes the salt bridge His5-Ile335 within a monomer. These changes profoundly and indirectly modify the allosteric transition and consequently the interactions of the dodecamer with carbamoylphosphate and effectors.

p53 gene mutations in oropharyngeal carcinomas: a comparison of solitary and multiple primary tumours and lymph-node metastases

Despite the steadily increasing number of patients suffering from squamous-cell carcinomas of the oropharyngeal region, little is known about the molecular steps involved in the induction of these neoplasms. We investigated oropharyngeal cancers from 38 patients for mutations in the p53 tumour-suppressor gene. The majority of patients (74%) had a history of tobacco and alcohol abuse. Five had lymph-node metastases, 3 had multiple primary carcinomas and 2 presented with multiple primary tumours and lymph-node metastases. Exons 5 through 8 of the p53 gene were screened by single-strand conformation polymorphism analysis followed by direct DNA sequencing. A total of 16 tumours (42%) contained point mutations which were scattered throughout exons 5 to 8. Most mutations (56%) were transitions, predominantly G-->A. Among the transversions, G-->T mutations prevailed; these have also been found in smoking-related lung cancer. One carcinoma of the soft palate showed a mutation which was retained in a lymph-node metastasis. In another patient, 2 primary carcinomas had different mutations, indicating that they had developed independently. Similar results were obtained in a case with a p53 mutation in the third of 3 primary tongue carcinomas which developed over a period of 23 years. One lymph-node metastasis had a 12-bp deletion which was not detected in any of the primary malignancies. The frequent occurrence of p53 mutations in oropharyngeal carcinomas supports the view that they play a role in the initiation or progression of the malignant phenotype.

In vitro identification of retinal ganglion cells in culture without the need of dye labeling

We here describe a method for the identification of a distinct neuronal phenotype at all stages of development in culture without the need of any staining procedure. Based purely on a size criterion we can rapidly select vital retinal ganglion cells (RGCs) for further studies out of a mixed culture of rat retinal cells. In order to establish a size criterion for retinal cells of various age, RGCs were first labeled immunocytochemically with antibody against the ganglion cell-specific surface glycoprotein Thy-1. Soma diameters were then determined for labeled and unlabeled cells between embryonic day 16 (E16) and postnatal day 90 (P90). Unlabeled neurons of all ages had soma diameters between 3.6 microns and 12 microns (mean diameter: 6.3 microns). In contrast, soma diameters of RGCs ranged from 8.4 microns to 28 microns and the number of RGCs with large soma diameters increased with age. Thus, in a mixed retinal cell culture only RGCs are larger than 12 microns and can be selected solely based on their size. The validity of the size criterion during the whole period of retinal cell differentiation offers the possibility to study the development of cellular functions and ion channel properties in a distinct type of cell without the risk of artifacts introduced by staining.

The adenovirus E4-6/7 protein transactivates the E2 promoter by inducing dimerization of a heteromeric E2F complex

Binding of the mammalian transcription factor E2F to the adenovirus E2a early promoter is modulated through interaction with the viral E4-6/7 protein. E4-6/7 induces the cooperative and stable binding of E2F in vitro to two correctly spaced and inverted E2F binding sites in the E2a promoter (E2F induction) by physical interaction in the protein-DNA complex. The E2a promoter is transactivated in vivo by the E4-6/7 product. The C-terminal 70 amino acids of E4-6/7 are necessary and sufficient for induction of E2F binding and for transactivation. To assess the mechanism(s) of E2a transactivation and the induction of cooperative E2F binding by the E4-6/7 protein, we have analyzed a series of point mutants in the functional C-terminal domain of E4-6/7. Two distinct segments of E4-6/7 are required for interaction with E2F. Additionally, and E4-6/7 mutant with a phenylalanine-to-proline substitution at amino acid 125 (F-125-P) efficiently interacts with E2F but does not induce E2F binding to the E2a promoter and is defective for transactivation. Induction of E2F stable complex formation at the E2a promoter by the F-125-P mutant protein is restored by divalent E4-6/7-specific monoclonal antibodies, but not a monovalent Fab fragment, or by appending a heterologous dimerization domain to the N terminus of the mutant protein. These and other data support the involvement of E4-6/7 dimerization in the induction of cooperative and stable E2F binding and transactivation of the E2a promoter. We present evidence that at least two cellular components are involved in E2F DNA binding activity and that both are required for E2F induction by the E4-6/7 product. The recently cloned E2F-related activities E2F-1 and DP-1 individually bind to an E2F binding site weakly, but when combined generate an activity that is indistinguishable from endogenous cellular E2F. Recombinant E2F-1, DP-1, and E4-6/7 are sufficient to form the induced E2F complex at the E2a promoter.

Anesthesia in a patient with acute respiratory insufficiency due to relapsing polychondritis

We report on a male patient with advanced relapsing polychondritis (RP), who was hospitalized for an ophthalmologic intervention. He had to undergo a tracheostomy with general anesthesia due to respiratory decompensation. RP is a rare systemic, inflammatory, and destructive disease of the cartilaginous structures leading to multiple functional disorders in the affected organs. Involvement of the tracheobronchial tract may cause severe respiratory problems and even life-threatening respiratory insufficiency. Treatment consists of corticoids, chemotherapy, antirheumatics, and surgical intervention. Anesthesiologic management requires careful preoperative evaluation of vital organ functions, in particular respiration, so that the anesthetic approach can be tailored to the individual needs of each patient.

[Proliferative myositis--a little-known pseudomalignant lesion]

The leading symptom of proliferative myositis is a rapidly growing hard tumor in the muscle. The disease is rare and therefore widely unknown. We observed a case of proliferative myositis in a 54-year-old female. We initially interpreted the hard tumor in the left musculus sternocleidomastoideus and its rapid growth as a malignant disease. The histological findings finally led to the correct diagnosis. In the light of the literature of 78 reported cases, a presumptive diagnosis can already be suspected from the clinical examination. The addition of CT scan and fine needle aspiration is highly diagnostic.

[Polychlorinated biphenyls as a cause of sterility in women?]

A total of 59 female infertile patients were investigated for the concentration of polychlorinated biphenyls (PCB) in their blood serum and follicular fluid. The average concentration of PCB in 66 related samples of follicular fluid and blood serum was 1.6 and 1.8 ng/ml, respectively. A splitting of the patients into two collectives, one with explained infertility, the other with unexplained infertility, showed no evidence of a higher PCB concentration in unexplained infertility patients. These results may exclude PCB as a primary reason for unexplained infertility.

The infratemporal fossa approach for adenoid cystic carcinoma of the skull base and nasopharynx

The infratemporal fossa approach to the skull base is an established method of treating neoplasms of this region. The type C variation has proved an effective means of removing adenoid cystic carcinoma invading the infratemporal fossa and skull base from the nasopharynx. A classification of these tumors is proposed, the surgical technique is described, and the results are given in this article.

Open laparoscopy for laparoscopic cholecystectomy

This report deals with the first 350 laparoscopic cholecystectomies performed at Creighton University, beginning in October 1989, by one of the authors (R.J.F., Jr.). An open technique was used for initial access to the abdominal cavity in 343 patients (98%). Patients included 274 females and 76 males, with an average age of 45.5 years. Weight ranged from 72 to 316 pounds (32-142.2 kg). The laparoscopic procedure was successfully completed in 338 (96.6%). Operative cholangiography was performed in 113 (32.3%), and 52 (14.7%) had acute cholecystitis as determined by the final pathological report. Median operating time was 80 min. There was no operative mortality. Bile duct injury was not seen. Postoperative complications occurred in 21 patients (6%), only two of which were directly related to the open technique (cellulitis of the umbilical wound requiring antibiotics). A third patient (0.3% of 343 successful laparoscopies) required reoperation on postoperative day 4 for a small bowel perforation; the exact cause could not be determined, but conceivably it was related to the umbilical minilaparotomy. We conclude that the open technique is safe and effective method for initial peritoneal access prior to laparoscopic cholecystectomy.

Radical mastoido-epitympanectomy with tympanoplasty and partial obliteration: a new surgical procedure?

The modern concept of an open cavity is to combine a safe with a dry, self cleansing ear. The prerequisites to achieve this goal are: the radical exenteration of the mastoid, antrum and epitympanum, the maximal reduction of the volume of the cavity by extensive lateral removal of bone and the adequate shaping of the cavity walls by obliteration of the bone pockets. To perform correctly a radical mastoido-epitympanectomy with tympanoplasty and partial obliteration is difficult and requires a perfect anatomical knowledge of the deepest regions of the temporal bone, particularly of the supralabyrinthine space. Using the technique exposed in this article, 75 out of 79 ears (95% of our revision cases) achieved a dry and self cleansing cavity at three years follow-up.

Candida endophthalmitis: clinical presentation, treatment and outcome in 23 patients

The presumptive diagnosis of Candida endophthalmitis was made in 11 intravenous (i.v.) drug addicts, seven surgical patients and five individuals with no established risk factors. It was based on the clinical symptoms with partial to total visual loss and the findings of a retinohyalitic lesion eventually affecting the entire eye. Empiric antimycotic treatment consisted of i.v. amphotericin B (average cumulative dose 1,580 mg) and i.v. or oral flucytosine (mean cumulative dose 231 g). This treatment resulted in a significant mean improvement of visual acuity from 0.15 to 0.275 during treatment and 0.55 after completion of therapy. Long-term results showed stable scar healing of the inflammatory lesions and stable to improved visual acuity. Transient side effects of treatment included anemia, thrombocytopenia and a rise of serum creatinine. Empiric antimycotic treatment of presumptive Candida endophthalmitis favourably influences the course of this infection. Regular ophthalmological examination of these patients is mandatory.

[Obstructive sleep apnea syndrome in a child with trisomy 21]

Pulmonary hypertension without any cardiovascular malformation was diagnosed by heart catheterization in a 4 year old girl with trisomy 21. A suspected obstructive sleep apnea syndrome was confirmed by polysomnography which revealed numerous obstructive apneas and hypopneas (apnea-index 23/h) with marked oxygen desaturation and a disturbed sleep pattern. Three months after adenotonsillectomy the mother reported her daughter having a quiet sleep without snoring. Polysomnography did not show any apnea nor any oxygen desaturation below 90%. A decrease of the pulmonary artery pressure was documented. Facial dysmorphias and muscle hypotonia predispose patients with trisomy 21 to obstructive sleep apnea, especially if hypertrophy of tonsills and adenoids coexist. Frequent arousals and hypoxia during sleep can result in failure to thrive and pulmonary hypertension. These consequences can be prevented by early diagnosis and treatment.

Feasibility of cellular microencapsulation technology for evaluation of anti-human immunodeficiency virus drugs in vivo

We investigated the feasibility of micro-encapsulation technology for the evaluation of anti-human immunodeficiency virus (HIV) drugs in vivo. The ability to place human cells in microcapsules with semipermeable membranes for implantation into test animals led to the development of this assay. The anti-HIV activity assay involves microencapsulating human T-lymphoblastoid cells sensitive to the cytopathic effects of HIV; the encapsulated cells are then implanted into athymic nude mice and recovered after drug treatment in vivo. A positive antiviral effect of the test substance is indicated by growth or survival of the virus-infected cells in the microcapsules. Several HIV-sensitive cell lines of T-lymphocyte, monocyte, and nonlymphocyte origin were examined for growth in microcapsules in vitro and in vivo. Light and electron microscopic analysis of the capsules and the human cells contained therein revealed the invasion of mouse immune cells and other adverse effects that could not be overcome by any of numerous technical modifications attempted. We conclude that cellular microencapsulation technology is not feasible for in vivo drug-testing protocols because of immunogenic reactions.

Differentiation of Al3+ and Al species in environmental samples by isotachophoresis

An isotachophoretic method for the determination of free [Al(H2O)6]3+ ions in different aluminium salt solutions was developed. The electrolyte system consists of 0.01 M sodium acetate (leading system) and 0.01 M tris(hydroxymethyl)amino-methane (terminating system). Separation was effected with a precapillary tube (diameter 0.05 cm) followed by a main capillary tube of length 20 cm and of smaller cross-section. The detection limit for [Al(H2O)6]3+ ions was 0.05 mg/l. The method was applied to the determination of free Al3+ ions ([Al(H2O)6]3+) in soil leachates and aqueous soil extracts.

Acidification of endosome subpopulations in wild-type Chinese hamster ovary cells and temperature-sensitive acidification-defective mutants

During endocytosis in Chinese hamster ovary (CHO) cells, Semliki Forest virus (SFV) passes through two distinct subpopulations of endosomes before reaching lysosomes. One subpopulation, defined by cell fractionation using free flow electrophoresis as "early endosomes," constitutes the major site of membrane and receptor recycling; while "late endosomes," an electrophoretically distinct endosome subpopulation, are involved in the delivery of endosomal content to lysosomes. In this paper, the pH-sensitive conformational changes of the SFV E1 spike glycoprotein were used to study the acidification of these defined endosome subpopulations in intact wild-type and acidification-defective CHO cells. Different virus strains were used to measure the kinetics at which internalized SFV was delivered to endosomes of pH less than or equal to 6.2 (the pH at which wild-type E1 becomes resistant to trypsin digestion) vs. endosomes of pH less than or equal to 5.3 (the threshold pH for E1 of the SFV mutant fus-1). By correlating the kinetics of acquisition of E1 trypsin resistance with the transfer of SFV among distinct endosome subpopulations defined by cell fractionation, we found that after a brief residence in vesicles of relatively neutral pH, internalized virus encountered pH less than or equal to 6.2 in early endosomes with a t1/2 of 5 min. Although a fraction of the virus reached a pH of less than or equal to 5.3 in early endosomes, most fus-1 SFV did not exhibit the acid-induced conformational change until arrival in late endosomes (t1/2 = 8-10 min). Thus, acidification of both endosome subpopulations was heterogeneous. However, passage of SFV through a less acidic early endosome subpopulation always preceded arrival in the more acidic late endosome subpopulation. In mutant CHO cells with temperature-sensitive defects in endosome acidification in vitro, acidification of both early and late endosomes was found to be impaired at the restrictive temperature (41 degrees C). The acidification defect was also found to be partially penetrant at the permissive temperature, resulting in the inability of any early endosomes in these cells to attain pH less than or equal to 5.3. In vitro studies of endosomes isolated from mutant cells suggested that the acidification defect is most likely in the proton pump itself. In one mutant, this defect resulted in increased sensitivity of the electrogenic H+ pump to fluctuations in the endosomal membrane potential.

A possible role for Na+,K+-ATPase in regulating ATP-dependent endosome acidification

Endosomes maintain a slightly acidic internal pH, which is directly responsible for their ability to ensure proper sorting of incoming receptors and ligands during endocytosis. At least two distinct subpopulations of endosomes can be distinguished, designated "early" and "late" on the basis of their kinetics of labeling with endocytic tracers. The subpopulations differ not only in their functions (rapid receptor recycling and transport to lysosomes, respectively) but also in their capacities for acidification in intact cells and in vitro. To investigate the possible basis for pH regulation in endosomes, we have studied the transport properties and ion permeabilities of early and late endosomes isolated from Chinese hamster ovary cells. Using endosomes selectively labeled with pH-sensitive endocytic tracers, we found that ATP-dependent acidification is electrogenic, being accompanied by the generation of an interior-positive membrane potential which opposes further acidification. While membrane potential and, consequently, acidification was controlled by the influx of permeant anions and efflux of protons and alkali cations, acidification was further modulated in Na+ and K+-containing buffers by the ouabain- and vanadate-sensitive Na+,K+-ATPase, which appears to be a functional component of the endosomal membrane. The data suggest that electrogenic Na+ transport due to Na+,K+-ATPase activity contributes to the interior-positive membrane potential, thereby reducing ATP-dependent H+ transport. Importantly, inhibition of acidification by Na+,K+-ATPase activity was found only in early endosomes, consistent with their limited acidification capacity relative to late endosomes and lysosomes.