Intensity-dependent scattering rings in high order above-threshold ionization.
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Journal Article↗
Biomedical subjects
B Walker
Publications and source records attributed to B Walker.
Peptide glyoxals: a novel class of inhibitor for serine and cysteine proteinases.
A series of novel synthetic dipeptides, containing a C-terminal glyoxal grouping (-COCHO), have been tested as inhibitors against typical members of the serine- and cysteine-proteinase families. For example, the sequences benzyloxycarbonyl (Cbz)-Pro-Phe-CHO (I) and Cbz-Phe-Ala-CHO (II), which fulfil the known primary and secondary specificity requirements of chymotrypsin and cathepsin B respectively, have been found to be potent reversible inhibitors of their respective target proteinase. Thus I was found to inhibit chymotrypsin with a Ki of approximately 0.8 microM, whereas II exhibits a Ki of approximately 80 nm against cathepsin B. These Ki values are some 10-fold and 3-fold lower than those reported for the corresponding peptide-aldehyde inhibitors of chymotrypsin and cathepsin B upon which the peptidyl-glyoxals were fashioned. Unexpectedly, the sequence Cbz-Pro-Ala-CHO, which was designed to inhibit elastase-like proteinases, exhibited no inhibitory activity towards porcine pancreatic elastase, even when used at concentrations as high as 200 microM.
Animals↗
Functional complementation of staphylococcal alpha-hemolysin fragments. Overlaps, nicks, and gaps in the glycine-rich loop.
The final steps in assembly of the lytic pore formed by staphylococcal alpha-hemolysin (alpha HL) involve the formation of a nonlytic oligomeric pore precursor, followed by the formation of a transmembrane channel. In this study, truncation mutants of alpha HL encompassing the NH2-terminal or COOH-terminal half of the polypeptide chain and all, part, or none of the central glycine-rich loop were obtained by in vitro, coupled transcription and translation of mutant plasmid DNAs. These polypeptides were unable to oligomerize upon or cause lysis of rabbit erythrocytes (rRBCs). Twenty-one pairs of the same truncation mutants constituting discontinuous alpha HL chains with overlaps, nicks, and gaps in the central loop were obtained by cotranslation. When incubated with rRBCs, many of the pairs were able to form hetero-oligomers with wild-type alpha-hemolysin (s-alpha HL) and most of these formed homo-oligomers in the absence of s-alpha HL. However, only members of a subset of these pairs were able to lyse the cells. The lytic combinations contained overlaps, nicks, or gaps, but only two pairs, with nicks between amino acid residues 128 and 129 and between 131 and 132 had hemolytic activities approaching that of the wild-type polypeptide. Active combinations could also be obtained by separately translating NH2- and COOH-terminal truncation mutants and then combining them. These findings suggest that the integrity of the central loop is of little significance for oligomer formation but that it is more important for the final step in pore assembly or alternatively for determining the correct structure of the conductive channel. Our findings disagree with previous reports of NH2- and COOH-terminal fragments with hemolytic activity and of the prevention of hemolysis by proteolytic cleavage in the central loop. This discord is attributed to experimental and interpretative ambiguities in the earlier protein chemistry. For example, we show that loss of hemolytic activity after treatment with trypsin is not due to cleavage after Lys-131, as previously proposed, but to the removal of a small NH2-terminal peptide through cleavage after Lys-8.
Amino Acid Sequence↗
Characterization of the cysteine proteinases of the common liver fluke Fasciola hepatica using novel, active-site directed affinity labels.
The excreted/secreted proteinases of adult and juvenile Fasciola hepatica maintained in vitro were found to hydrolyse the fluorogenic substrates Cbz-Phe-Arg- and Cbz-Arg-Arg-NHMec. This activity was demonstrated to have a classical cysteine proteinase inhibitor profile, with turn-over of both substrates being blocked by pre-incubation with E64 and peptidyl diazomethanes. The Cbz-Arg-Arg-NHMec hydrolysing activity of the mature fluke exhibited an alkaline stability not characteristic of its mammalian lysosomal counterparts. Further, the biotinylated affinity reagents biotin-Phe-Ala-CHN2 and biotin-Phe-Cys(SBzyl)-CHN2 were used to label and characterize these cysteine proteinases in terms of apparent molecular weight and subsite specificity. Adult fluke media were found to contain four species of molecular weights 66, 58, 50 and 25-26 kDa; juvenile media contained three species of molecular weights 66, 54 and 25-26 kDa. The major 25-26 kDa cysteine proteinase common to both stages was shown to have a subsite specificity similar to that of mammalian cathepsin B.
Affinity Labels↗
1H-nuclear magnetic resonance studies of human synovial fluid in arthritic disease states as an aid to confirming metabolic activity in the synovial cavity.
1. A 1H-n.m.r. method was used to measure concentrations of valine, alanine, lactate, acetate, hyaluronan and lipids in synovial fluid obtained, during the normal course of examination from the knee joints of patients attending rheumatology and orthopaedic clinics. Fluid was available from 16 patients with osteoarthritis, 18 patients with rheumatoid arthritis, four patients with meniscal tear and one patient each with systemic lupus erythematosis, mono-arthritis, synovitis and loose bodies. Four normal specimens were obtained for comparison. 2. Valine, alanine and acetate levels all showed a normal Gaussian distribution, reflecting the distributions within the serum of the sample population. 3. Lactate concentrations divided into two distinct patterns. At concentrations below 2.5 mmol/l the lactate levels showed a Gaussian distribution, reflecting the distribution in normal serum. The normal synovial fluid specimens belong to this distribution. Above 2.5-3.0 mmol/l, lactate levels were asymmetric in distribution with a long tail at higher concentrations. These high levels of lactate can be explained by the generation of lactate through anaerobic metabolism within the synovial cavity. This metabolic process is triggered by a general inflammatory condition such as in rheumatoid arthritis. 4. The distribution of n.m.r.-observable lipid concentrations in rheumatoid arthritis and osteoarthritis each shows a normal distribution and the mean concentration is significantly higher in rheumatoid arthritis. 5. An increased n.m.r.-observable hyaluronan concentration is associated with an inflammatory situation. 6. It is concluded that raised levels of lactate and n.m.r.-observable hyaluronan and lipids are useful markers to aid the clinical distinction between rheumatoid arthritis and osteoarthritis.(ABSTRACT TRUNCATED AT 250 WORDS)
Acetates↗
[Hermaphroditism verus: clinical aspects, diagnosis and therapy in adulthood].
A 20-year old woman, who underwent an intersex operation during infancy, was presented for evaluation of the gonads because of suspected true hermaphroditism. The phenotype was female with regular menstruations. Examination revealed an ovarian tumour of 8 cm on the left side and a normal right ovary. During the operation, the tumour was revealed as an endometriosis cyst, which could be excised whilst preserving the ovarian tissue. The right gonad was an ovotestis. The testicular part was removed because of a 4% risk of malignancy. The different combinations of ovary/testis and ovotestis are described. Diagnosis and therapy of true hermaphroditism should be performed as early as possible to obtain an adequate gonadal function and an undisturbed psychosexual development.
Adult↗
Double ionization in the perturbative and tunneling regimes.
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Journal Article↗
Infection in the transplanted and native lung after single lung transplantation.
OBJECTIVE: To analyze a single-center experience with infectious complications of single lung transplantation (SLT) with special emphasis on risk factors for infection in the transplanted and native lung. DESIGN: Consecutive case series. SETTING: University teaching hospital. PATIENTS: Fifteen consecutive SLT recipients (mean age, 43 years; 9 men and 6 women). Mean follow-up was 337 days. RESULTS: Fifteen patients had 24 infectious episodes (1.6 per patient) of which 83 percent were life-threatening, 79 percent involved the lung, airway, or pleural space, and 79 percent occurred in the first 4 months after transplantation. Despite this high infectious morbidity, there were no infectious deaths. The most important infections were bacterial pneumonia (n = 10), cytomegalovirus (CMV) pneumonia (n = 5), and bronchial anastomotic infections (n = 3). Significant risk factors for bacterial pneumonia were a diagnosis of primary or secondary pulmonary hypertension (p < 0.05) and the presence of airway complications of stenosis or dehiscence (p < 0.05). No risk factors for overall lung infections were identified. The native lung was involved in 6 of 16 lung infections and was the exclusive site of infection in 4 cases. Underlying disease in the native lung may have predisposed to infection at that site by a mechanism of inadequate blood flow or impaired ventilation. Three bronchial anastomotic infections (Pseudomonas, Candida, Aspergillus) occurred, all with dehiscence of the anastomosis. These were highly morbid but resolved with antibiotics, stent placement, and surgical retention in two of the three cases. The five episodes of CMV pneumonia caused mild (four patients) or moderate (one patient) dysfunction and responded to antiviral agents without relapse. CONCLUSION: The frequency, complexity, and morbidity of infections after SLT were great, but most infections were manageable and good outcomes were achieved. A pretransplant diagnosis of pulmonary hypertension or posttransplant occurrence of bronchial stenosis or dehiscence were associated with a higher rate of bacterial pneumonia. The underlying disease in the native lung may predispose to infection at that site.
Adolescent↗
Vitamin D Deficiency in the Morbidly Obese.
Although vitamin D deficiency has been well-documented following gastric bypass surgery, there are few studies of vitamin D status in the non-operative morbidly obese patient. We examined 25-hydroxyvitamin D (25-OHD) levels in 60 morbidly obese pre-operative females; 62% of them had 25-OHD levels below normal range (16-74 ng/ml) which were not associated with reductions in serum calcium or phosphorus, liver or kidney dysfunction, and were not significantly correlated to patients' age. However, 25-OHD levels were significantly (p < 0.0001) and negatively correlated to body mass (r = -0.49). These data suggest that low vitamin D may be associated with obesity per se. Hypovitaminosis D, when it is found in post-bariatric surgery patients, may not be caused by the surgery since it may have been present to some degree pre-operatively.
Journal Article↗
Cortisol and hypertension: what was not so apparent about "apparent mineralocorticoid excess".
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11-beta-Hydroxysteroid Dehydrogenases↗
Bacterial growth in blood for transfusion.
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Bacteremia↗
Assembly of the oligomeric membrane pore formed by Staphylococcal alpha-hemolysin examined by truncation mutagenesis.
The alpha-hemolysin (alpha HL) from Staphylococcus aureus causes the lysis of susceptible cells such as rabbit erythrocytes (rRBCs). Lysis is associated with the formation of a hexameric pore in the plasma membrane. Here we show that truncation mutants of alpha HL missing 2 to 22 N-terminal amino acids form oligomers on the surfaces of rRBCs but fail to lyse the cells. By contrast, mutants missing 3 or 5 amino acids at the C terminus are very inefficient at oligomerization but do lyse rRBCs, albeit extremely slowly. The C-terminal truncation mutants, retarded as monomers on the cell surface, undergo a conformational change in which the protease-sensitive loop located near the midpoint of the polypeptide chain becomes occluded. Judged by this criterion, polypeptides truncated at the N terminus, frozen as nonlytic oligomers, are in a similar conformation. A second proteolytic site near the N terminus of the polypeptide becomes inaccessible in the lytic pore formed by the wild-type polypeptide, supporting the idea that a second conformational change occurs upon pore formation. These findings suggest a pathway for assembly of the lytic pore in which alpha HL first binds to target cells as a monomer, which is converted to a nonlytic oligomeric intermediate before formation of the pore. In keeping with this model, an N-terminal truncation mutant blocks the slow lysis induced by a C-terminal truncation mutant, presumably by diverting the weakly lytic subunits into inactive oligomers.
Amino Acid Sequence↗
Functional expression of the alpha-hemolysin of Staphylococcus aureus in intact Escherichia coli and in cell lysates. Deletion of five C-terminal amino acids selectively impairs hemolytic activity.
The alpha-hemolysin gene from Staphylococcus aureus, excluding the 5' region encoding the hydrophobic leader sequence, was amplified from genomic DNA. The identity of the disputed C terminus has been confirmed and revisions made to the internal sequence. The hemolysin is expressed at high levels in Escherichia coli and has been purified to homogeneity from this source. In addition, active [35S-Met]alpha-hemolysin of high specific radioactivity can be generated in an E. coli transcription-translation system. By criteria based on protein chemistry, and biological and electrophysiological assays, the recombinant polypeptide is closely similar to the staphylococcal polypeptide ruling out the possibility of functionally important posttranslational modifications in S. aureus. Convenient new assays utilizing the 35S-labeled polypeptide to measure erythrocyte binding, oligomer formation in detergent and on target cells, and hemolysis have been developed. They have been used to demonstrate that a deletion mutant of alpha-hemolysin, in which five C-terminal amino acids are absent, is severely compromised in its ability both to oligomerize and to lyse rabbit erythrocytes. The mutant polypeptide nevertheless binds tightly to erythrocytes as a monomer, strengthening the idea that oligomerization is required for cell lysis.
Animals↗
The synthesis, kinetic characterization and application of a novel biotinylated affinity label for cathepsin B.
In this study we report on the synthesis, kinetic characterization and application of a novel biotinylated and active-site-directed inactivator of cathepsin B. Thus the peptidyldiazomethane biotinyl-Phe-Ala-diazomethane has been synthesized by a combination of solid-phase and solution methodologies and has been shown to be a very efficient inactivator of bovine and human cathepsin B. The respective apparent second-order rate constants (k0bs./[I]) for the inactivation of the human and bovine enzymes by this reagent, namely approximately 5.4 x 10(4) M-1.min-1 and approximately 7.8 x 10(4) M-1.min-1, compare very favourably with those values determined for the urethane-protected analogue benzyloxycarbonyl-Phe-Ala-chloromethane first described by Green & Shaw [(1981) J. Biol. Chem. 256, 1923-1928], thus demonstrating that the presence of the biotin moiety at the P3 position is compatible with inhibitor effectiveness. The utilization of this reagent for the detection of cathepsin B in electrophoretic gels, using Western blotting and in combination with a streptavidin/alkaline phosphatase detection system, is also demonstrated. Given that the peptidyldiazomethanes exhibit a pronounced reactivity towards cysteine proteinases, we feel that the present label may well constitute the archetypal example of a wide range of reagents for the selective labelling of this class of proteinase, even in a complex biological milieu containing additional classes of proteinases.
Affinity Labels↗
The synthesis, kinetic characterization and application of biotinylated aminoacylchloromethanes for the detection of chymotrypsin and trypsin-like serine proteinases.
The synthesis of two biotinylated affinity labels for chymotrypsin and trypsin-like serine proteinases is described, along with their kinetic characterization and application to the detection of these proteinases after PAGE and Western blotting. Thus the chloromethane analogues biotinylphenylalanylchloromethane (Bio-Phe-CH2Cl; reagent 1) and biotinylarginylchloromethane (Bio-Arg-CH2Cl, reagent 2), have been shown to be potent active-site-directed inactivators of chymotrypsin and trypsin respectively. The apparent overall second-order rate constants (kobs./[I]) for the inactivation of chymotrypsin and trypsin by reagent 1 (approximately 4.9 x 10(3) M-1.min-1) and reagent 2 (approximately 1.0 x 10(5) M-1.min-1) respectively are comparable with those obtained by other workers with simple urethane-protected analogues and demonstrates that the presence of the bulky biotinyl moiety is compatible with inhibitor effectiveness. Samples of chymotrypsin and trypsin that have been inactivated by reagents 1 and 2 respectively and which have been subjected to SDS/PAGE and Western blotting can be revealed with a streptavidin/alkaline phosphatase label. We can presently detect down to 20 ng of inactivated proteinase by using this system. The utility of the arginine derivative for the detection of the plasma trypsin-like proteinases plasmin and thrombin has also been demonstrated, thus holding out the possibility that this reagent may find general application as an active-site-directed label for this class of proteinase.
Affinity Labels↗
The application of a novel biotinylated affinity label for the detection of a cathepsin B-like precursor produced by breast-tumour cells in culture.
In this report we demonstrate how the recently developed biotinylated affinity label biotinyl-Phe-Ala-diazomethane (Bio-Phe-Ala-CHN2) [Cullen, McGinty, Walker, Nelson, Halliday, Bailie & Kay (1990) Biochem. Soc. Trans. 18, 315-316; Walker, Cullen, Kay, Halliday, McGinty & Nelson (1992) Biochem. J. 283, 449-453] can be used for the detection of a precursor form of a cathepsin B-like enzyme produced by breast-tumour cells in culture. Thus the cell lines MDA-MB-436, ZR-75-1 and T47-D produce a soluble protein that can be allowed to react with the biotinylated affinity label to yield an SDS-resistant complex; this can be revealed with a streptavidin/alkaline phosphatase label after PAGE and Western blotting. This protein (molecular mass 47 kDa) can also be detected by immunoblotting using sheep anti-(cathepsin B) antibodies in conjunction with a donkey anti-sheep IgG label. None of the cell lines studied produced any mature cathepsin B-like activity, as gauged by the lack of turnover of the fluorogenic substrate benzyloxycarbonyl-Arg-Arg-4-methylcoumarin-7-ylamide (Cbz-Arg-Arg-NH-Mec). However, treatment of medium samples with pepsin resulted in the generation of such activity. When the pepsin-catalysed activation step was analysed by SDS/PAGE, the protein of 47 kDa was completely converted into two species of very similar molecular masses of 30.5 kDa and 29 kDa. Both these proteins can incorporate the biotinylated probe and, in common with the 47 kD species, they can be detected with the streptavidin/alkaline phosphatase label and immunoblotting. We propose that the 47 kD form is the pepsin-activable proform of these lower-molecular-mass species. The release of the proform from the oestrogen-receptor (ER)-positive breast-tumour cell lines ZR-75-1 and T47-D is stimulated 5-10-fold when these cells are grown in medium containing epidermal growth factor (EGF) at a concentration of 10 ng/ml. In contrast, there is no modulation in the amount of proform released by the ER-negative cell line MDA-MB-436, over a range of EGF concentrations from 0 to 100 ng/ml.
Affinity Labels↗
Catalytic subunits of Aplysia neuronal cAMP-dependent protein kinase with two different N termini.
Previously, two forms of cAMP-dependent protein kinase catalytic subunit generated by mutually exclusive use of two internal exon cassettes (A1 and A2) were demonstrated in Aplysia neurons. Here, it is shown that there also exist catalytic subunits with alternative N termini derived from two exons, N1 and N2, expressed in combination with either of the internal cassettes. Processed transcripts including N1 or N2 sequences are of about equal abundance in the nervous system, arise through alternative promoter use, and encode catalytically active polypeptides. The N2 amino acid sequence is 21 residues longer than the N1 sequence and is homologous to the nonmyristoylated N terminus of the TPK1 gene product, a yeast catalytic subunit homolog. These data support the view that cAMP-dependent protein kinase activity in Aplysia neurons is produced by a complex array of regulatory and catalytic subunits that generate multiple holoenzymes with a spectrum of properties.
Amino Acid Sequence↗