Multimodality treatment of a multifocal osteoblastoma-like tumor of the lower extremity

Osteoblastoma-like tumor is a rare condition with limited information on its orthopedic management in the current medical literature. The tumor histologically resembles an osteoblastoma, although the radiographic features are similar to those observed in primary vascular lesions. The treatment in the previously reported cases involved aggressive procedures including amputation, en bloc resection, and chemotherapy because of the uncertainty regarding the biological behavior of the tumor. We present a case of this entity that was successfully treated by a combination therapy including intralesional curettage with adjuvant cryotherapy, in situ and intravenous administration of bisphosphonates and radioablation.

Tibial tubercle fragmentation: a clue to simultaneous patellar ligament avulsion in pediatric tibial tubercle fractures

Simultaneous avulsions of the tibial tubercle and patellar ligament have been reported, but are rare. We present an 11-year-old boy who was initially diagnosed with a Type IIIA tibial tubercle avulsion fracture after falling off of his bicycle. Intraoperatively, following exposure and fixation of the tibial tubercle fragment, knee range of motion under live fluoroscopy revealed a stationary patella with no tension in the patellar ligament. The incision was extended and a distal avulsion of the patellar ligament from the tibial tubercle was identified, with a small flap of tibial tubercle periosteum remaining attached. Transosseous suture fixation of the avulsed periosteal flap was achieved with 2 No. 5 ethibond sutures placed through connecting drill holes. Postoperatively, the patient was placed in a long leg cast with the knee in extension for 6 weeks. The injury to healed and the patient returned to full activities, although he required 2 courses of physical therapy and 4.5 months to regain full range of motion. Preoperative diagnosis of simultaneous tibial tubercle fracture and patellar ligament avulsion can be difficult. Palpation of the patellar ligament for gaps may not be possible due to a large knee effusion. Most patients do not tolerate quadriceps testing on examination and do not have patella alta on radiographs. In retrospect, a clue to this diagnosis in our patient was the preoperative radiographic finding of multiple calcified fragments below the patella. The calcified fragments likely represent the avulsed tibial tubercle periosteum attached to the distal patellar ligament. In addition, the large tibial tubercle fragment is separated and rotated superiorly, a finding that was also noted in two other similar case reports.

Case report: treatment of open femoral shaft fracture in a severely burned patient

OBJECTIVE

To present a case report of a patient with an open fracture and severe burns and review the literature.

METHODS

The patient was treated with intubation, intravenous antibiotics, and debridement and intramedullary nailing for the femur fracture. He later underwent multiple burn excision procedures with allograft and autograft skin coverage. The wound over the fracture was treated with dressing changes. The fracture was treated with nail exchange and bone grafting for atrophic nonunion.

RESULTS

The patient was returned to full weightbearing and good function with a fully healed femur.

CONCLUSIONS

Treatment of open fractures in burn patients should be tailored to the specific needs of the individual; they should be reduced and stabilized via internal fixation at the earliest opportunity and should be managed by minimizing wound colonization through successive debridement, wound care, and consideration of flap coverage.

Rates of perioperative complications associated with laminectomies in patients with achondroplasia

BACKGROUND

Lumbar decompressive surgery can be complicated by dural tears, infection, nerve root injury, deep venous thrombosis, and epidural hematoma. However, perioperative complications of multilevel laminectomies in patients with achondroplasia rarely are reported. Our objective was to determine the perioperative complication rates associated with laminectomies in patients with achondroplasia.

METHODS

We reviewed the medical records of the initial laminectomies for all ninety-eight patients with achondroplasia at our institution, which included twenty-eight patients who had had previous spine surgeries at other institutions, and determined the rates of complications in the following categories: neurologic, pulmonary, cardiovascular, and gastrointestinal complications; intraoperative dural tears; infections at the incision site; and mortality.

RESULTS

Sixty (61%) of ninety-eight patients had at least one perioperative complication. By category, these included intraoperative dural tears, which occurred in 37% (thirty-six patients); neurologic complications, in 23% (twenty-three patients); infections at the incision site, in 9% (nine patients); deep venous thrombosis, in 3% (three patients); pulmonary complications, in 3% (three patients); and gastrointestinal complications, in 3% (three patients). The only death was caused by a pulmonary embolism.

CONCLUSIONS

Perioperative complications are common in patients with achondroplasia undergoing multilevel laminectomies, and the perioperative care team should be aware of these complications when caring for these patients.

Laminectomies and achondroplasia: does body mass index influence surgical outcomes?

Obesity is a widespread and potentially serious health problem in individuals with achondroplasia. In addition to obesity, such individuals commonly experience lumbar spinal stenosis. Although laminectomies have long been the method of choice for thorough lumbar decompression, to the best of our knowledge, the relationship between body mass index (BMI) and surgical outcomes after laminectomy in patients with achondroplasia has not been investigated in a large patient population. Through a retrospective medical record review of the initial laminectomies of all individuals with achondroplasia at our institution for whom adequate records were available, we evaluated the influence of BMI on surgical outcomes after laminectomy via four criteria: (1) change in Rankin score; (2) change in walking distance; (3) intra-operative and post-operative complications; and (4) need for subsequent revision laminectomies. The 49 individuals (mean BMI: 31.5 kg/m(2) at the time of laminectomy) were stratified into the standard BMI categories: normal (<25 kg/m(2)), overweight (25-29.9 kg/m(2)), obese Class I (30-34.9 kg/m(2)), and a combined obese Class II (35-39.9 kg/m(2)) and obese Class III (>40 kg/m(2)). Our analysis indicated that there was no statistical difference between these groups in terms of the four criteria. When the study group was categorized into non-obese (normal weight and overweight) and obese (obese Classes I and II/III) groups, there was also no statistically significant improvement difference in terms the same four criteria. Our data suggest that obesity does not pose additional risks to laminectomy in individuals with achondroplasia.

Tip of the trade: a method of splinting for surgeons

Mallet fingers are difficult to treat, especially in surgeons, who need to sterilize their hands continuously and who have constant strains placed on their fingers. We successfully treated a nondominant, fifth-digit, nonbony mallet finger in a surgical resident with a splint method composed of a bent, semitubular, small-fragment plate and Steri-strips (3-M, St. Paul, MN). This splinting method allowed the resident to continue performing surgeries while the injury healed.

Band 3 is a target protein of spectrin's E2/E3 activity: implication for sickle cell disease and normal red blood cell aging

We have demonstrated that a 125 kDa red blood cell (RBC) membrane protein, being a target of spectrin's E2/E3 activity, is ubiquitinated band 3. This demonstration was based on copurification of this biotinylated-ubiquitinated protein with band 3, immunoprecipitation with band 3 antibody and analysis of proteins associated with strepavidin sepharose by micro liquid chromatography coupled to tandem mass spectrometry (microLC/MS/MS). Further, we demonstrated the presence of ubiquitinated band 3 in vivo by Western blotting of purified band 3 with a monoclonal antibody (FK2) against ubiquitin. The implications of these results for sickle cell disease and RBC aging are discussed.

Ankyrin is a target of spectrin's E2/E3 ubiquitin-conjugating/ligating activity

Ubiquitin is a small protein of 8.6 kDa molecular weight. When polyubiquitin is attached to target proteins, they are tagged for destruction by cytoplasmic organelles called proteasomes. We now know that ubiquitination of target proteins also regulates functions as diverse as the sorting of proteins to different intracellular destinations, cell signaling, cell division, gene transcription, and protein-protein interactions. The ubiquitination of target proteins requires a cascade of enzymes: E1 ubiquitin activating enzyme, E2 ubiquitin conjugating enzyme and E3 ubiquitin ligating enzyme. Recently we have demonstrated that the red blood cell (RBC) membrane skeletal protein, spectrin, has E2/E3 enzymatic activities in its alpha-subunit, that can transfer ubiquitin to itself. We have now created a cell free assay using biotinylated ubiquitin that allows detection of target proteins by streptavidin peroxidase. This approach coupled with immunoprecipitation, purification and micro liquid chromatography coupled to tandem mass spectrometry has identified ankyrin as a target of spectrin's E2/E3 activity. Western blotting, with ubiquitin antibody, of purified ankyrin and its well characterized functional domains, has demonstrated that both the spectrin and band 3 binding domains are ubiquitinated in vivo.

Watch out for the K-wire: painful experiences in two cases

According to reviews in the literature, only a few case reports have mentioned the unusual migration of K-wires during orthopaedic surgery since 1991. This report emphasises the potential migration of the K-wire during plastic surgery in order to avoid the possible catastrophic complications.

Role of individual monomers of a dimeric initiator protein in the initiation and termination of plasmid rolling circle replication

Plasmids of the pT181 family encode initiator proteins that act as dimers during plasmid rolling circle (RC) replication. These initiator proteins bind to the origin of replication through a sequence-specific interaction and generate a nick at the origin that acts as the primer for RC replication. Previous studies have demonstrated that the initiator proteins contain separate DNA binding and nicking-closing domains, both of which are required for plasmid replication. The tyrosine residue at position 191 of the initiator RepC protein of pT181 is known to be involved in nicking at the origin. We have generated heterodimers of RepC that consist of different combinations of wild type, DNA binding, and nicking mutant monomers to identify the role of each of the two monomers in RC replication. One monomer with DNA binding activity was sufficient for the targeting of the initiator to the origin, and the presence of Tyr-191 in one monomer was sufficient for the initiation of replication. On the other hand, a dimer consisting of one monomer defective in DNA binding and the other defective in origin nicking failed to initiate replication. Our results demonstrate that the monomer that promotes sequence-specific binding to the origin must also nick the DNA to initiate replication. Interestingly, whereas Tyr-191 of the initiator was required for nicking at the origin to initiate replication, it was dispensable for termination, suggesting that alternate amino acids in the initiator may promote termination but not initiation.

Interleukin-4 mediates cell growth inhibition through activation of Stat1

Interleukin-4 (IL-4) activates Stat6 (signal transducer and activator of transcription 6) and plays multiple roles in regulation of the immune system. IL-4 also triggers phosphorylation of insulin receptor substrate (IRS), leading to stimulation of cell growth. Moreover, IL-4 inhibits proliferation of a variety of cells, but the molecular mechanism of its growth inhibitory effect is not understood. In this study, we demonstrated that IL-4 inhibited cell growth of colon carcinoma cell lines (HT29 and WiDr) but promoted cell growth of Burkitt's lymphoma cell lines (BL30 and BL41) in a dose-dependent manner. The growth inhibition was not dependent on Stat6 activation, because Stat6 was activated at similar levels in all cell lines in response to IL-4. Strikingly, IL-4 activated Stat1 in colon carcinoma cell lines but not in Burkitt's lymphoma cell lines. Therefore, these results suggest that IL-4 induced Stat1 activation, resulting in growth inhibition of colon carcinoma cell lines. Importantly, we present evidence that Stat1 is necessary for IL-4-mediated growth inhibition using Stat1-deficient and Stat1-reconstituted cells. The growth inhibitory effect of IL-4 was diminished in Stat1-deficient cells, whereas it was restored in Stat1-reconstituted cells. In addition, the expression of dominant-negative Stat1 in HT29 cells led to the loss of growth inhibition in response to IL-4. Taken together, our data suggest that IL-4 activates Stat1, leading to cell growth inhibition in colon cancer cells. Thus, this study demonstrates, for the first time, a molecular mechanism by which IL-4 inhibits cell growth.

Restoration of partially edentulous patients using customized implant abutments

The ideal placement of implants is not always possible in partially edentulous patients. The diverse and unique implant positions that occur in clinical practice may be difficult or impossible to restore through the use of conventional abutments. Customized abutments permit the fabrication of aesthetic restorations that correct deficiencies in implant angulation, alignment, and position. These abutments also enhance the soft tissue emergence profile of the restorations and allow the prosthetic margins to be properly positioned in all dimensions. Additional benefits include ease of treatment delivery and comparative expense.

Determination of benzodiazepines in clinical serum samples: comparative evaluation of REMEDi system, aca analyzer, and conventional HPLC performance

Emergency toxicology or drug screening in clinical settings requires rapid qualitative and quantitative analysis with acceptable levels of sensitivity and specificity. The aim of this study was to comparatively evaluate the performance of the multi-column HPLC-based REMEDi drug profiling system (Bio-Rad), the aca analyzer (Du Pont), and the bench standard conventional HPLC method in the identification of 12 clinically important benzodiazepines. In this study, the presence of benzodiazepines in 133 patients' serum samples were qualitatively and comparatively analyzed by these three procedures. Among these methods, 120 of 133 samples were identified as benzodiazepine-positive by conventional HPLC (90%); 127 by aca analyzer (95%); and 84 by REMEDi (63%). Detection sensitivity of REMEDi for most of the benzodiazepines was found satisfactory when concentrations were greater than 1.0 microg/mL. When benzodiazepine concentrations were in the ranges of 0.3-1.0 microg/mL, detection sensitivity became varied among the benzodiazepine family of drugs by REMEDi method. REMEDi procedure should not be considered as the method of choice for detection of benzodiazepines if expected concentration levels are below 0.3 microg/mL, with the exception of bromazepam. Conventional HPLC displayed the highest sensitivity and specificity for the detection of benzodiazepines. In our studies, 36 REMEDi-negative samples were positive by HPLC, although in 16 of the 36 REMEDi negative samples (13.3%), the presence of benzodiazepines was detected but only listed as candidates without positive identification of the individual compounds by REMEDi. In our series, however, there were no false positives by the REMEDi method whereas aca procedure showed 13 false positive results (9%) and 6 cases of false negative (4%). Our data indicate that the REMEDi procedure can be used on serum samples for rapid qualitative screening of clinically important high levels of benzodiazepines with high specificity. However, due to the relatively low sensitivity of REMEDi in samples with low benzodiazepine levels and relatively low specificity by aca, all samples should be further confirmed by conventional HPLC procedure.

Burkholderia pseudomallei infection in the Singapore Armed Forces from 1987 to 1994--an epidemiological review

Between 1987 and 1994, twenty-three cases of Burkholderia pseudomallei infection (melioidosis) were diagnosed in persons serving in the Singapore Armed Forces. There were four deaths resulting from complications of the infection. Unlike the situation in the general population, where the affected are mainly the elderly with underlying illness, the majority of cases in the Singapore Armed Forces were otherwise fit and healthy young servicemen. Serological surveys have shown the prevalence of the infection in Singapore to be 0.2% in the military as well as civilian population. As physical contact with soil is an unavoidable part of military training, military personnel continue to be at risk of exposure to this soil-related disease.

Characterization of primary lesions caused by the plastome mutator of Oenothera

Oenothera plants homozygous for a recessive allele at the plastome mutator (pm) locus show non-Mendelian mutation frequencies that are 1000-fold higher than spontaneous levels. Characterization of RFLP sites in a collection of mutants indicates that insertion-deletion hot spots in the pm lines are defined by tandem direct repeats, implicating replication slippage or misalignment during recombination. Several sites known to contain very short direct repeats were examined, and all were found to have been targeted in one or more plants of the mutant collection. To determine if replication slippage was occurring, two oligo-A stretches in non-coding DNA were examined, and 3 of 12 plants were found to have an additional adenine in a 13-base track. To search for other mutations that would not be visible as restriction fragment length polymorphisms, PCR-amplification products of the psbB gene were digested with a restriction endonuclease, denatured, and examined for single-strand conformational polymorphisms. Among 21 mutants, one 4-bp insertion and one point mutation were identified in psbB. The discovery that the plastome mutator can cause base substitutions as well as repeat-mediated insertions and deletions points to a likely defect in a component of the cpDNA replication machinery.

Inhibition of vesicular stomatitis virus RNA synthesis by protein hyperphosphorylation

Vesicular stomatitis virus (VSV) RNA synthesis requires the template nucleocapsid, the polymerase (L) protein, and the cofactor phosphorylated (P/NS) protein. To determine whether the degree of phosphorylation regulated VSV RNA synthesis, infected Chinese hamster ovary cells were treated with okadaic acid (OKA), a serine/threonine phosphatase inhibitor. OKA reduced viral penetration and uncoating but had little or no effect on primary transcription or viral protein synthesis. However, approximately 80% of total viral RNA synthesis was inhibited when 2 microM or more OKA was added to infected cells after viral uncoating had taken place. Analysis of proteins and RNA species in infected cells labeled with 32P showed that OKA led to hyperphosphorylation of two viral phosphoproteins, the P/NS protein and matrix protein (M), resulting in inhibition of full-length RNA synthesis and subsequent secondary transcription. Pulse-chase experiments demonstrated that the hyperphosphorylated P/NS species was converted rapidly from the less phosphorylated form. Hyperphosphorylated P/NS as well as the less phosphorylated form, but not M, were found to be associated with nucleocapsids isolated from cytoplasmic extracts. These results suggest that phosphorylation played an important role in the regulation between viral transcription and viral RNA replication as well as the turning off of RNA replication. Thus, phosphatase inhibitors promise to be a valuable tool for dissecting the regulatory mechanisms involving phosphorylated viral proteins.

Detection of specific antibody to mycobacterial antigen 60 in tuberculous pleural effusion

BACKGROUND

With the development of the enzyme-linked immunosorbent assay (ELISA) method, serodiagnosis of tuberculosis has been studied by many investigators. Only a few studies have been performed in pleural fluid. This study was designed to evaluate the IgG antibody levels to mycobacterial antigen 60 (Ag60) in pleural fluid, and evaluate its role in the diagnosis of tuberculous pleurisy.

METHODS

Eighteen patients with tuberculous pleural effusions and 18 patients with malignant pleural effusions were studied. The levels of IgG antibodies to Ag60 in pleural fluids were measured by ELISA method.

RESULTS

The mean titers of IgG against Ag60 in pleural fluids of tuberculous patients (508.3 +/- 382.7 EU) were significantly higher than those of the mean value of the malignant group (131.2 +/- 83.2 EU). In the TB pleurisy group, patients with positive M. tuberculosis cultures from pleural fluids had significantly higher titers than those with negative cultures (796.5 +/- 394.7 vs 277.8 +/- 150.2 EU); patients with impaired immune function had significantly lower titers than those without (138.4 +/- 28.9 vs 650.6 +/- 358.1 EU). Using 250 EU as a cutoff value for a positive test, the sensitivity was 72.2% and the specificity, 94.4%.

CONCLUSIONS

ELISA method using Ag60 is a rapid test with an acceptable sensitivity and excellent specificity for differentiation between tuberculous and malignant pleural effusion.

Anergy in immature B lymphocytes. Differential responses to receptor-mediated stimulation and T helper cells

We have compared the responses of purified neonatal and adult B lymphocytes to stimulation by anti-Ig antibodies, which are functional analogues of Ag, and by Th cells. Neonatal B cells are markedly deficient in proliferative responses to anti-Ig antibodies + IL-4 or to anti-Ig conjugated to dextran, both of which induce strong proliferation of adult B cells in the absence of T lymphocytes. Anti-Ig antibodies actually inhibit the functional responses of neonatal B cells, even to polyclonal stimuli such as LPS. However, Th cells induce both proliferation and Ig secretion by neonatal B cells in the presence of Ag that bind to B cell Ig and are subsequently presented by the B cells. Thus, in neonatal B lymphocytes, cross-linking of membrane Ig in the absence of Th cells has a net inhibitory effect, and this inhibition is overcome by T cell help. These results also suggest that unresponsiveness or tolerance to thymus-independent Ag is induced in the B cells themselves, but tolerance to thymus-dependent proteins resides primarily in the T cell compartment.

Anergy in immature B lymphocytes. Differential responses to receptor-mediated stimulation and T helper cells

We have compared the responses of purified neonatal and adult B lymphocytes to stimulation by anti-Ig antibodies, which are functional analogues of Ag, and by Th cells. Neonatal B cells are markedly deficient in proliferative responses to anti-Ig antibodies + IL-4 or to anti-Ig conjugated to dextran, both of which induce strong proliferation of adult B cells in the absence of T lymphocytes. Anti-Ig antibodies actually inhibit the functional responses of neonatal B cells, even to polyclonal stimuli such as LPS. However, Th cells induce both proliferation and Ig secretion by neonatal B cells in the presence of Ag that bind to B cell Ig and are subsequently presented by the B cells. Thus, in neonatal B lymphocytes, cross-linking of membrane Ig in the absence of Th cells has a net inhibitory effect, and this inhibition is overcome by T cell help. These results also suggest that unresponsiveness or tolerance to thymus-independent Ag is induced in the B cells themselves, but tolerance to thymus-dependent proteins resides primarily in the T cell compartment.

Activation of functionally distinct subsets of CD4+ T lymphocytes

The studies summarized in this review have established that cloned lines of CD4+ T cells that produce distinct cytokines differ markedly in their responses to different forms of antigenic stimulation. Furthermore, we are beginning to develop experimental systems for better defining the signals that stimulate the differentiation of resting T cells into functionally distinct subsets. From these studies it is possible to construct the following hypothetical model for the differentiation of mature CD4+ T cells. Resting cells produce IL2 as the principal growth factor, IFN gamma, and little or no IL4. Antigenic stimulation in the presence of IL4 (which may be produced by non-T cells) leads to the preferential expansion of IL4-producing cells. These cells secrete their cytokines maximally when stimulated with antigens presented by B cells, which are also the principal targets of these cytokines. Continued expansion of IL4-producing T cells may require antigen exposures that also stimulate the production of IL1 by macrophages. In the absence of IL4 and IL1 (and in the presence of costimulators that are not yet defined) the T cells that are preferentially expanded belong to the IL2-producing subset. In addition, each subset may produce cytokines that stimulate the expansion of that subset and inhibit the other (Fiorentino et al., 1989). It is apparent that a number of assays and reagents need to be developed if these results are to be extended to physiologic immune responses. First, it is important to identify surface molecules that may serve as phenotypic markers for functionally distinct subsets of CD4+ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneity of helper/inducer T lymphocytes. III. Responses of IL-2- and IL-4-producing (Th1 and Th2) clones to antigens presented by different accessory cells

Murine CD4+ T cell clones have been classified into at least two subsets, Th1 and Th2, on the basis of their distinct lymphokine secretion profiles and functions. In the present study, we compared the functional responses of Th1 and Th2 clones to Ag presentation by splenic B cells and peritoneal macrophages. Th2 clones secreted IL-4 in response to Ag presented by resting B cells, but their optimal proliferation required the addition of IL-1 or a source of IL-1. The degree of IL-1 dependence varied among the four Th2 clones examined. In contrast, Th1 clones secreted IL-2 and proliferated in response to Ag presented by both B cells and macrophages, without any requirement for exogenous IL-1. Furthermore, the proliferation of Th2 clones in response to Ag presented by splenocytes or macrophages was inhibited by an IL-1R antagonist. These results indicate that IL-1 is an important costimulator for the expansion of the Th2 subset of CD4+ T cells. The different requirements for the proliferation of Th1 and Th2 cells may be responsible for the preferential expansion of one or the other subset under different conditions of immunization.

In vitro processing of proopiocortin by membrane-associated and soluble converting enzyme activities from rat intermediate lobe secretory granules

Secretory granules (SGs) from rat intermediate lobes (IL) were isolated in a highly purified form by differential centrifugation, followed by sucrose density gradient centrifugation. The purified IL-SGs were lysed by freezing and thawing. The granule lysate was then centrifuged to generate membrane and soluble fractions. Proopiocortin -converting enzyme (PCE) activity was assayed by incubation of [3H]arginine- or [3H] phenylalanine-labeled toad proopiocortin with the total granule lysate, the membrane, or the soluble fraction at pH 5.0. The processed products were identified by immunoprecipitation with ACTH and beta-endorphin antisera, followed by acid-urea-gel electrophoresis. The PCE activity in rat IL-SG lysate cleaved proopiocortin to 21,000 mol wt ACTH, 21,000 mol wt ACTH/lipotropin (LPH), 13,000 mol wt ACTH, beta LPH, beta-endorphin-like peptides, and alpha MSH-like peptides, similar to those synthesized by the toad intermediate lobe in situ. Treatment of the PCE cleavage products with carboxypeptidase B resulted in the liberation of free arginine. This observation together with the nature of the products formed suggest that the PCE activity cleaved at pairs of basic residues of proopiocortin , yielding one or more products that terminated with an arginine or an arginine-lysine. PCE activity was found in membrane and soluble granule fractions, and both activities were inhibited by leupeptin, p-chloromercuribenzoate, dithiodipyridine, and pepstatin A, but not by chloroquine or N-alpha-p-tosyl-L-lysine-chloromethylketone HCl. Diisopropyl fluorophosphate and other thiol protease reagents (p-chloromercuriphenyl sulfonic acid, iodoacetic acid, and HgCl2) had a small inhibitory effect. The products formed by PCE activities in the membrane and soluble fractions were similar to those cleaved by the total granule lysate. The membrane fraction primarily cleaved proopiocortin between ACTH and beta LPH to form 21,000 (21 K) mol wt ACTH and beta-LPH, similar to the first processing step in the IL in situ. The soluble fraction, however, showed a greater tendency to cleave proopiocortin between the 16 K N-terminal glycopeptide and ACTH, to yield twice as much 21 K ACTH/LPH product as the membrane fraction. The membrane-associated PCE activity was found to be easily solubilized by extraction with high salt (1 M NaCl), suggesting that it is not an integral granule membrane protein.

Characterization of proopiocortin converting activity in rat anterior pituitary secretory granules

Lysates from purified secretory granules of rat anterior pituitary glands were incubated with [3H]phenylalanine or [3H]arginine-labeled toad proopiocortin. The processed products formed were identified by immunoprecipitation with ACTH and beta-endorphin antisera, and by comigration with known markers on acid-urea polyacrylamide gels. Proopiocortin was cleaved by the secretory granule lysate primarily to 21,000 mol wt ACTH, 13,000 mol wt ACTH, 16,000 mol wt NH2-terminal glycopeptide, beta-lipotropin, a beta-endorphin-like peptide, and beta-endorphin. Characterization of the anterior pituitary proopicortin-converting activity shows that it: (1) cleaves specifically at the peptide bond on the carboxy side of the lysine-arginine residues of proopiocortin, (2) has a pH optimum in the acidic range, (3) is present in membrane and soluble fractions of the granule lysate, and (4) is inhibited by leupeptin, pepstatin A, and 2,2' dithiodipyridine, but not by p-chloromercuribenzoate, diisopropyl fluorophosphate, N alpha-p-tosyl-L-lysine chloromethyl ketone hydrochloride, chloroquine, L-1-tosylamide-2-phenylethyl-chloromethyl ketone, or EDTA.

Proopiocortin-converting enzyme activity in bovine neurosecretory granules

Neurosecretory granules (NSGs) from neural lobes of bovine pituitary glands were isolated in a highly purified form by metrizamide-sucrose gradient centrifugation. The purified NSGs were lysed and centrifuged, and the supernatants were further fractionated by gel filtration on Sephadex G-75. Proopiocortin-converting enzyme activity was assayed by incubation of [3H]arginine- or [3H]phenylalanine-labeled toad proopiocortin with NSG supernatant fractions. The processed products were identified by immunoprecipitation with ACTH and beta-endorphin antisera, followed by acid-urea gel electrophoresis. The optimum pH for the enzyme-mediated conversion was around pH 5.0. Conversion of toad proopiocortin by NSG converting enzyme activity was inhibited by leupeptin, antipain, p-chloromercuribenzoate, and pepstatin A, but not by diisopropyl fluorophosphate, EDTA, or N-alpha-p-tosyl-L-lysine-chloromethyl ketone HCl. The results suggest that the proopiocortin-converting enzyme activity in bovine neurosecretory granules is due to an acid-thiol protease which may contain secondary hydrophobic binding sites that are involved in substrate recognition.

Pro-opiocortin processing in the pituitary: a model for neuropeptide biosynthesis

The biosynthesis of alpha-MSH, beta-endorphin and ACTH in the pituitary is reviewed. These neuropeptides are synthesized from a common pro-protein, pro-opiomelanocortin. The pro-protein is cleaved intragranularly, at pairs of basic residues in the molecule to yield the respective peptide products. An unique, thiol protease (pro-opiocortin converting enzyme) and a carboxypeptidase B-like enzyme, both localized within pituitary secretory granules and having a pH optimum of 5-6, appear to be involved in the proteolytic processing of pro-opiomelanocortin.

Stability differences between high coagulant (alpha) and noncoagulant (gamma) human thrombins. Denaturation

Human alpha-thrombin, the two (covalently linked)-chain, highly coagulant blood-clotting enzyme was compared with its noncoagulant, yet estero/amidolytically active derivative, gamma-thrombin, a three (noncovalently associated)-domain enzyme which results from two proteolytic cleavages of the coagulant a form. Studies of their denaturation behavior by Tos-Arg-OMe esterase activity, by intrinsic fluorescence, by fluorescence of active serine-directed dansyl labels, and by monitoring the ESR of a fluorosulfonylphenyl spin-labeled inhibitor clearly demonstrated the reduced stability of the noncovalently associated gamma-thrombin form. At pH 6.5, 0.75 M NaCl, gamma-thrombin unfolds in approximately 2. 1 M urea while the more stable a form denatures at approximately 4 M urea. By monitoring active serine probes (spin label or fluorescent labels), these transitions were slightly lower, 1.0 +/- 0.1 and 2.8 +/- 0.2 M urea for spin-labeled gamma- and alpha-thrombins, respectively. Similar behavior was found for the same spin-labeled derivatives in guanidine HCl with unfolding transitions of 0.4 M and 1.0 M for spin-labeled gamma- and alpha-thrombin, respectively. These differences in structural stabilization serve as a good physical diagnostic for the two thrombin species.

Refolding of a three (noncovalently linked)-domain enzyme. Human gamma-thrombin

Human gamma-thrombin is a three (noncovalently linked)-domain enzyme which contains the known serine protease catalytic triad, Asp-His-Ser, one on each of the three noncovalent domains (Asp 99 on the A-B3 chain). While protein-folding dogma does not necessarily predict that the denatured form of this enzyme could refold to the correct conformation, a monitor of the esterase activity (Tos-Arg-OMe) shows complete recovery of native catalytically active conformation. When compared with the covalently intact alpha form which refolds from urea in less than 2 min with complete return of both clotting and esterase activity, gamma-thrombin requires up to 90 min to regain full esterase activity. The gamma-thrombin reactivation data best fit a single first order rate constant, k = 0.03 +/- 0.005 min-1. It was suggested that the gamma-thrombin renaturation process might represent first the rapid refolding, then subsequent reassociation and reisomerization of the three noncovalent domains to yield a lower energy, fully active, conformation. This study represents the only example known of the refolding (reconstitution) of a three (noncovalent)-domain protein.

Cobalt iontophoresis of sensory nerves in the rat lung

By iontophoretically introducing, first, cobalt and, subsequently, sulfide ions into the vagus nerve, it is possible to trace sensory nerves to their endings in the rat lung. Nerve fibers and terminals are found predominantly in the adventitia of the airways and blood vessels. Some nerves are found in the submucosa of the bronchi and bronchioles. Some are found in the cardiac muscle on the periphery of pulmonary veins, and a few nerves are seen to end among smooth muslces of the blood vessels and the airways. At least three types of nerve endings can be identified at the light microscopic level: (1) free nerve endings; (2) brush-like endings; (3) knob-like terminals.