Dynamics of the flexible loop of triosephosphate isomerase: the loop motion is not ligand gated

Using solid-state deuterium NMR, we have measured the motion of the flexible loop of triosephosphate isomerase (TIM) with and without substrate and transition-state analogs. The measurements were carried out on a catalytically competent mutant of TIM W90Y W157F containing a single tryptophan (W168) in the flexible loop; W168 is the only strictly conserved tryptophan in the currently available TIM sequences. The solid-state NMR samples were prepared by precipitation using polyethylene glycol, and kinetic analysis of the PEG-precipitated TIM gave values for kcat, Km, and KI similar to those measured in solution for the substrate and substrate and transition-state analogs. Deuterium NMR spectra of samples prepared with tryptophan labeled at the indole positions with and without any substrate or analogs indicate that the loop jumps between two conformations at a rate of 3 x 10(4) s-1 (from the predominant to the less populated form) with a population ratio of 10:1. Surprisingly, spectra of TIM ligated with a substrate analog, glycerol 3-phosphate (G3P), or with a tight-binding transition-state analog, phosphoglycolate (PGA), show that the loop moves with a rate similar to the rate in the empty enzyme and also has a similar population ratio for the two conformers. This observation indicates that loop closure is not ligand gated but is a natural motion of the protein. Furthermore, the measured rate is approximately matched to the turnover time. We did not observe a signal for TIM labeled with alpha-deuteriotryptophan, although it was prepared in a fashion analogous to the ring-labeled sample and had a specific activity and protein concentration comparable to the latter. For this deuterium concentration, we would expect to observe the NMR signal unless the deuterium relaxation were very slow. The hypothesis that the spin-lattice relaxation of the alpha-deuteron is very slow would be consistent with the observed dynamics of the ring-deuterated TIM.

ENDOR studies of the primary donor cation radical in mutant reaction centers of Rhodobacter sphaeroides with altered hydrogen-bond interactions

The electronic structure of the cation radical of the primary electron donor was investigated in genetically modified reaction centers of Rhodobacter sphaeroides. The site-directed mutations were designed to add or remove hydrogen bonds between the conjugated carbonyl groups of the primary donor, a bacteriochlorophyll dimer, and histidine residues of the protein and were introduced at the symmetry-related sites L168 His-->Phe, HF(L168), and M197 Phe-->His, FH(M197), near the 2-acetyl groups of the dimer and at sites M160 Leu-->His, LH(M160), and L131 Leu-->His, LH(L131), in the vicinity of the 9-keto carbonyls of the dimer. The single mutants and a complete set of double mutants were studied using EPR, ENDOR, and TRIPLE resonance spectroscopy. The changes in the hydrogen bond situation of the primary donor were accompanied by changes in the dimer oxidation midpoint potential, ranging from 410 to 710 mV in the investigated mutants [Lin, X., Murchison, H. A., Nagarajan, V., Parson, W. W., Williams, J. C. & Allen, J. P. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269]. It was found that the addition or removal of a hydrogen bond causes large shifts of the spin density between the two halves of the dimer. Measurements on double mutants showed that the unpaired electron can be gradually shifted from a localization on the L-half of the dimer to a localization on the M-half, depending on the hydrogen bond situation. As a control, the effects of the different hydrogen bonds on P.+ in the mutant HL(M202), which contains a BChlL-BPheM heterodimer as the primary donor with localized spin on the BChl aL [Bylina, E. J., & Youvan, D. C. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7226-7230; Schenck, C. C., Gaul, D., Steffen M., Boxer S. G., McDowell L., Kirmaier C., & Holten D. (1990) in Reaction Centers of Photosynthetic Bacteria (Michel-Beyerle M. E., Ed.) pp 229-238, Springer, Berlin] were studied. In this mutant only small local changes of the spin densities (< or = 10%) in the vicinity of the hydrogen bonds were observed. The effects of the introduced hydrogen bonds on the spin density distribution of the dimer in the mutants are discussed in terms of different orbital energies of the two BChl a moieties which are directly influenced by hydrogen bond formation. The observed changes of the spin density distribution for the double mutants are additive with respect to the single mutations.(ABSTRACT TRUNCATED AT 400 WORDS)

Relationship between the oxidation potential of the bacteriochlorophyll dimer and electron transfer in photosynthetic reaction centers

The primary electron donor in the photosynthetic reaction center from purple bacteria is a bacteriochlorophyll dimer containing four conjugated carbonyl groups that may form hydrogen bonds with amino acid residues. Spectroscopic analyses of a set of mutant reaction centers confirm that hydrogen bonds can be formed between each of these carbonyl groups and histidine residues in the reaction center subunits. The addition of each hydrogen bond is correlated with an increase in the oxidation potential of the dimer, resulting in a 355-mV range in the midpoint potential. The resulting changes in the free-energy differences for several reactions involving the dimer are related to the electron transfer rates using the Marcus theory. These reactions include electron transfer from cytochrome c2 to the oxidized dimer, charge recombination from the primary electron acceptor quinone, and the initial forward electron transfer.

Coxiella burnetii antibody prevalences among human populations in north-east Africa determined by enzyme immunoassay

Retrospective serosurveys were conducted to determine the prevalence of antibody to phase-I Coxiella burnetii among humans in various locations of north-east Africa. Sera were tested by the enzyme immunoassay (EIA). Initially the EIA was compared with the standard indirect fluorescent antibody (IFA) method for the detection of antibody to C. burnetii. Results indicated that the EIA was slightly less sensitive (88%), but highly specific (94%) and less subjective than the IFA technique. EIA was subsequently adopted for estimating prevalences in the studied human populations. Data obtained by EIA indicated that the prevalence of C. burnetii antibody among adult Egyptian blood donors was 20% (n = 358) in the Suez Canal area, 16% (n = 501) in the Nile Valley and 10% (n = 427) in the Nile Delta. Among adult patients with acute, undifferentiated fever in Egypt, the prevalence was 28% (n = 50) of acute sera, with seroconversion in 12% of convalescent sera. Antibody to C. burnetii was detected by EIA in the sera of 25% (n = 71) of cattle workers in Egypt, 10% (n = 100) of housewives in Sudan, and 37% (n = 104) of adults in north-west Somalia. Following a fever outbreak affecting all ages in northern Sudan, IgG antibody to C. burnetii was present in 54% of the febrile persons (n = 185) and in 53% of afebrile persons (n = 186). IgM antibody to C. burnetii was demonstrated in 29% of the febrile persons and 15% of the afebrile persons. These results implicate C. burnetii as a possibly important and under-reported cause of human disease and undiagnosed fevers in north-east Africa.

Correlation between multiple hydrogen bonding and alteration of the oxidation potential of the bacteriochlorophyll dimer of reaction centers from Rhodobacter sphaeroides

The electronic absorption and vibrational Raman spectra of mutant reaction centers from Rhodobacter sphaeroides bearing multiple site-specific mutations near the primary electron donor (P), a bacteriochlorophyll dimer, are reported. These mutations bear double and triple combinations of single-point mutations that alter the H-bonding interactions between histidine residues and the C2- and C9-conjugated carbonyl groups of the primary donor [Mattioli, T.A., Williams, J.C., Allen, J.P., & Robert, B. (1994) Biochemistry 33, 1636-1643] and change the donor redox midpoint potential from 410 to 765 mV compared to 505 mV for wild type [Lin, X., Murchison, H.A., Nagarajan, V., Parson, W.W., Williams, J.C., & Allen, J.P. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269]. Near-infrared Fourier transform Raman spectroscopy was used to determine the changes in H-bonding interactions of the primary donor in these multiple mutants. The Fourier transform Raman spectra of the mutants exhibit the predicted changes in hydrogen bond interactions of the P carbonyl groups with the protein, and they are consistent with the designed mutations. Moreover, the Raman data verify that the H-bonds formed or broken in the multiple mutants are similar in strength to those observed in the corresponding single mutants. A correlation was observed between the change in P/P.+ redox midpoint potential and the total change in H-bonding interaction energy (from -207 to 364 meV relative to wild type) as gauged by the estimated enthalpy of each H-bond formed or broken on the four conjugated carbonyls of the primary donor. Only minor changes were observed in the optical spectra of the mutant reaction centers, indicating that the addition of H-bonds from histidines has little effect in destabilizing the first electronic excited state of the dimer relative to the ground state. However a blue shift in the dimer absorption band at ca. 890 nm at 20 K was associated with the removal of the H-bond to the C2 acetyl carbonyl group via His L168. A red shift of the oxidized dimer band at ca. 1250 nm was associated with the formation of each H-bond to the C9 keto carbonyl groups.

Comparative efficacy of levamisole, thiabendazole and fenbendazole against cattle gastrointestinal nematodes

Efficacy of two older anthelmintics, levamisole and thiabendazole, was compared with a newer benzimidazole, fenbendazole, against naturally acquired gastrointestinal nematode infections in cattle superimposed with experimental infections of Bunostomum phlebotomum and Dictyocaulus viviparus. Twenty-four crossbred beef heifers of 7-9 months of age and 152 kg in average weight were randomly allocated to four groups of six calves. The cattle grazed on pastures contaminated with larvae of gastrointestinal nematodes and the lungworm for 2 months prior to Day 0. Treatment groups were as follows: Group 1--levamisole, topical at 10 mg kg-1; Group 2--thiabendazole paste at 110 mg kg-1; Group 3--fenbendazole paste at 10 mg kg-1; Group 4--untreated controls. All calves were necropsied for worm recovery between 8 and 10 days after treatment. Fecal egg/larval per gram counts at 18 and 42 h post-treatment indicated greatest reductions in Groups 1 and 2. By 7 days post-treatment, reduction in counts for all treated groups ranged from 99.1 to 100%, except for the 66.7% reduction of B. phlebotomum in Group 2. Seven nematode species were present in a sufficient number of untreated controls for valid efficacy assessment at necropsy. Efficacy of fenbendazole was 100% against all species, including Cooperia spp. L4 and immature (E5) D. viviparus. The overall efficacy of levamisole and thiabendazole was generally high (93.0-100% against Haemonchus placei adults, Cooperia punctata and C. spatulata adult males, Cooperia spp. adult females, Oesophogastomum radiatum, B. phlebotomum, and D. viviparus adults).(ABSTRACT TRUNCATED AT 250 WORDS)

Paraphimosis in elderly men

Paraphimosis occurs when the foreskin of the penis is retracted over the glans and cannot be replaced in its normal position. The tight ring of preputial skin constricts the distal penis causing vascular occlusion, much like a tourniquet. The condition is painful and, if not dealt with quickly, can lead to necrosis of the glans. Simple reduction of the prepuce can be achieved by compressing the edematous fluid out of the glans and repositioning the foreskin. Irreducible paraphimosis is treated by dorsal slit procedure and subsequent circumcision. We present two cases illustrating the treatment techniques and possible complications of paraphimosis in men.

Efficacy of Coxiella burnetii and its chloroform-methanol residue (CMR) fraction against Rift Valley fever virus infection in mice

Strains of Coxiella burnetii phase I and II whole cells (WC-I and WC-II) or whole cell fractions were assessed for their potential to induce long-lasting protection in endotoxin-non-responder C3H/HeJ or CD-1 mice against Rift Valley fever (RVF) virus challenge. Among the whole cell fractions, only the chloroform-methanol residue (CMR), administered as a single dose (100 micrograms per mouse) 24 h before viral challenge, effectively protected 100% of the mice from RVF virus; the CMR of the Ohio strain of C. burnetii was not protective. Most of the RVF virus-infected mice treated with other C. burnetii cell fractions died, although their times to death varied. Lipopolysaccharide (LPS) associated with CMR preparations used in these studies, did not protect against RVF virus challenge. A single dose of 100 micrograms of CMR given 24 h before viral challenge completely eradicated 4-5 logs of RVF virus in the serum, liver, spleen, and central nervous system. Compared to several other immunomodulators, CMR was an equally effective antiviral agent. Efficacy of CMR of both Henzerling and Ohio strains disappeared or was marginal when treatment was initiated 2-3 days before RVF viral challenge, even when a second or a third dose of CMR was administered after challenge. A single dose of liposome-encapsulated CMR to RVF virus-infected mice extended the range of therapeutic efficacy of this biologically active component of C. burnetii to 4 days before infection.

Effect of treatment with an ivermectin sustained-release bolus on productivity of stocker beef calves

Three groups of 30 crossbred beef steers, 8-10 months of age and ranging in weight from 158 to 320 kg, were used to compare effects of treatment with an ivermectin sustained-release bolus or two ivermectin injectable treatments on parasite control and productivity in relation to untreated controls during a 168 day winter-spring grazing period. Each group of 30 consisted of five cattle on each of six separate 1.6 ha pastures. Treatments on Day 0 (12 December) were: Group 1: untreated controls; Group 2: ivermectin injectable at 200 micrograms kg-1 bodyweight, s.c., on Day 0 and Day 56; Group 3: ivermectin sustained-release bolus to deliver ivermectin at 12 mg day-1 over approximately 135 days. All cattle were weighed at 28 day intervals and fecal samples were collected for egg per gram counts (EPG). Geometric mean EPG for Group 3 remained consistently less than 1.0 after Day 0 and were highest (2.4) on Day 168. All group EPG were significantly different (P < 0.01) by Day 56, and EPG of Group 2 had increased to 10.5 following initial treatment and to 42.8 on Day 112. With the exception of a low mean EPG of 6.8 for Group 1 on Day 112, EPG of the group were consistently highest (range 24.9-36.0) to the end of the experiment. Ostertagia ostertagi was predominant, along with smaller proportions of Haemonchus placei and Cooperia spp. Throughout the experiment Group 3 had highest liveweights and gains that were most often different from those of Group 1 at P < 0.01 or greater.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell-mediated and humoral immune responses after vaccination of human volunteers with the live vaccine strain of Francisella tularensis

The specific humoral and cell-mediated immune responses of human volunteers vaccinated with the Francisella tularensis live vaccine strain (LVS) were evaluated. In the search for an optimal antigen to measure the immunogenicity of the vaccine in an enzyme-linked immunosorbent assay, we tested irradiation-killed LVS, an aqueous ether extract of the LVS (EEx), lipopolysaccharide (LPS) from LVS, and a virulent strain (SCHU4). Volunteers were immunized with LVS by scarification. Immunoglobulin G (IgG) responses to LVS and LPS gave the highest background titers when tested with sera from unimmunized volunteers, whereas IgA, IgG, and IgM background titers to EEx and SCHU4 were low. Vaccination caused a significant rise (P < 0.01) in IgA, IgG, and IgM titers to all antigens tested, except for the IgG response to LPS. Eighty percent of vaccinated volunteers developed a positive IgG response to EEx 14 days postvaccination, while 50% were positive to LVS. By day 14 after vaccination, 70% of immunized volunteers exhibited a positive response to EEx in an in vitro peripheral blood lymphocyte proliferation assay. EEx, a specific and sensitive antigen for evaluating immune responses of vaccinated volunteers, may be a superior antigen for the diagnosis of tularemia.

Nutritional therapy for pregnant women with a metabolic disorder

Nutritional therapy is essential for a normal reproductive outcome in phenylketonuric women. In homocystinuria, fetal outcome is good in women whose disorder is responsive to vitamin B6 therapy and is poor in women whose disorder is unresponsive to therapy. Pregnancy in galactosemia is rare because of the almost universal ovarian dysfunction present in female patients with this disorder. Transplantation of the fertilized ovum is a promising possibility for these women. In women with MSUD, there has been only one case of pregnancy reported to date.

Acquired renal cystic disease and renal cell carcinoma in an allograft kidney

Acquired renal cystic disease has been reported in the kidneys of patients with end stage renal disease who have been untreated, treated with dialysis or undergone renal transplantation. The incidence of renal tumor development in patients with acquired renal cystic disease is greater than 5% in those undergoing chronic hemodialysis. Recently, cases of renal cell carcinoma occurring with acquired renal cystic disease of the native kidneys of transplant recipients have been reported. Transplant patients have an increased incidence of malignancy when compared to the general population. Including our case, 19 cases of de novo renal neoplasms developing in renal allografts have been reported. To the best of our knowledge we report the longest interval to presentation of a de novo renal tumor in an allograft kidney (228 months) and the first case of renal cell carcinoma associated with acquired renal cystic disease in an allograft kidney.

Nonpeptidic inhibitors of human leukocyte elastase. 6. Design of a potent, intratracheally active, pyridone-based trifluoromethyl ketone

Further modification of the 3-amino substituent in a trifluoromethyl ketone-based series of 3-amino-6-phenylpyridin-2-ones that had been optimized for oral activity led to analogs that were potent intratracheal inhibitors in a model of HLE-induced lung damage in the hamster. The best 3-amino substituent for intratracheal activity is [4-[N-[(4-chlorophenyl)sulfonyl]-carbamoyl]phenyl]sulfonyl. At a 30 min prechallenge interval, compound 9, which incorporates this substituent, had an ED50 of approximately 2 nmol/animal and, qualitatively, afforded a very similar dose-response relationship to that found with a peptidic trifluoromethyl ketone inhibitor, ICI 200,355.

Laminin and fibronectin content of mouse glomerular and tubular basement membrane

Because the glomerular basement membrane (GBM) is subject to damage in a multitude of renal diseases, a model of basement membrane permeability properties would be useful for learning more about this important barrier. Isolated, perfused tubular basement membrane (TBM) allows measurement of permeability, but it is not known whether TBM is similar enough to GBM for data to be extrapolated from this model to the glomerulus. As a first approach to assessing differences between GBM and TBM, we looked at composition. Renal glomeruli and tubules were isolated from Swiss-Webster mice by sucrose-gradient centrifugation. GBM and TBM were isolated by sonication in 1% deoxycholate and then subjected to a sequential extraction procedure. Analysis of the solubilized basement membranes by electrophoresis revealed a complex mixture of proteins. Immunoblot analysis demonstrated that, among the proteins, laminin and fibronectin were found exclusively in the guanidine and guanidine/dithiotreitol extracts. The total amount of laminin extracted in GBM, 1.8 +/- 0.001 micrograms/mg dry weight (n = 2 groups animals, by inhibitory ELISA), was significantly less than in TBM, 3.4 +/- 0.1 micrograms/mg dry weight (n = 2); however, the total amount of fibronectin extracted did not differ between GBM and TBM, 8.2 +/- 0.8 and 7.7 +/- 1.0 micrograms/mg dry weight (n = 2) respectively. Examination of deoxycholate supernatants was carried out to see if components of GBM or TBM were solubilized during isolation of basement membranes. Immunoblot analysis revealed loss of some laminin and fibronectin occurred during the detergent isolation of GBM and TBM. We conclude that GBM and TBM are qualitatively similar in that they have the same protein components, but differ significantly in content of laminin and probably other macromolecular components.

Metastatic renal cell carcinoma presenting as a skin nodule: case report and review of the literature

Cutaneous metastasis from renal cell carcinoma is unusual. A patient is described who presented with a solitary skin metastasis 6 months after unilateral radical nephrectomy for renal cell carcinoma. In most instances, once cutaneous involvement is manifest the disease is widespread and has a poor prognosis. The skin should be examined during tumor evaluation as part of the physical examination and skin lesions in patients with renal cell carcinoma should be evaluated aggressively to rule out cutaneous metastasis.

Relationship between rate and free energy difference for electron transfer from cytochrome c2 to the reaction center in Rhodobacter sphaeroides

The rate of electron transfer from cytochrome c2 to the bacteriochlorophyll dimer of the reaction center from the photosynthetic bacterium Rhodobacter sphaeroides has been investigated using time-resolved optical spectroscopy. Measurements were performed on a series of mutant reaction centers in which the midpoint potentials of the bacteriochlorophyll dimer vary over a range of 350 mV. Dramatic changes in the characteristic time of electron transfer were observed, with the measured values ranging from 7730 to 80 ns compared to 960 ns for wild type. The binding constants (0.15 to 0.25 microM-1) and the second-order rate constants for the slow component (5.5 x 10(8) to 9.4 x 10(8) M-1 s-1) for the mutants are similar to the corresponding values for wild type (0.35 microM-1 and 11 x 10(8) M-1 s-1), indicating that the binding of the cytochrome to the reaction center is not changed in the mutants. In the mutants with the fastest rates, an additional minor component was resolved that is probably due to formation of a reaction center-cytochrome complex in an unfavorable configuration with a binding constant an order of magnitude weaker than the major component. The altered midpoint potentials in the mutants result in values for the free energy difference for this electron transfer reaction ranging from -65 to -420 meV compared to -160 meV for wild type. The relationship between the rate and free energy difference was well fit by a Marcus equation using a reorganization energy of 500 meV.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific alteration of the oxidation potential of the electron donor in reaction centers from Rhodobacter sphaeroides

The effects of multiple changes in hydrogen bond interactions between the electron donor, a bacteriochlorophyll dimer, and histidine residues in the reaction center from Rhodobacter sphaeroides have been investigated. Site-directed mutations were designed to add or remove hydrogen bonds between the 2-acetyl groups of the dimer and histidine residues at the symmetry-related sites His-L168 and Phe-M197, and between the 9-keto groups and Leu-L131 and Leu-M160. The addition of a hydrogen bond was correlated with an increase in the dimer midpoint potential. Measurements on double and triple mutants showed that changes in the midpoint potential due to alterations at the individual sites were additive. Midpoint potentials ranging from 410 to 765 mV, compared with 505 mV for wild type, were achieved by various combinations of mutations. The optical absorption spectra of the reaction centers showed relatively minor changes in the position of the donor absorption band, indicating that the addition of hydrogen bonds to histidines primarily destabilized the oxidized state of the donor and had little effect on the excited state relative to the ground state. Despite the change in energy of the charge-separated states by up to 260 meV, the mutant reaction centers were still capable of electron transfer to the primary quinone. The increase in midpoint potential was correlated with an increase in the rate of charge recombination from the primary quinone, and a fit of these data using the Marcus equation indicated that the reorganization energy for this reaction is approximately 400 meV higher than the change in free energy in wild type. The mutants were still capable of photosynthetic growth, although at reduced rates relative to the wild type. These results suggest a role for protein-cofactor interactions--in particular, histidine-donor interactions--in establishing the redox potentials needed for electron transfer in biological systems.

Bilateral testicular carcinoma in situ in persistent müllerian duct syndrome: a case report and literature review

Bilateral testicular carcinoma in situ in a 17-year-old patient with persistent müllerian duct syndrome is reported. The pertinent literature is reviewed and the management of both testicular carcinoma in situ and persistent müllerian duct syndrome is discussed.

Neurotransmitter receptor agonists regulate growth hormone gene expression in cultured ovine pituitary cells

The regulation of growth hormone (GH) secretion and GH mRNA content by the dopaminergic agonist, bromocriptine (BRO); the beta-adrenergic agonist; isoproterenol (ISO); the alpha 1-adrenergic agonist, methoxamine (MET); the alpha 2-adrenergic agonist, clonidine (CLON); the serotonergic agonist, quipazine (QUIP); somatostatin (SS) and GH-releasing hormone (GHRH) were studied using cultured ovine anterior pituitary cells. Clonidine and BRO (10(-6) M) inhibited basal and GHRH (10(-10) M)-stimulated GH release. Bromocriptine enhanced GH mRNA content and potentiated the GHRH (10(-8) M)-stimulated content of GH mRNA, while CLON had no effect on GH mRNA. Quipazine had little effect on GH secretion and no effect on GH mRNA content. Methoxamine and ISO (10(-6) M) increased basal secretion of GH and both enhanced GHRH-stimulated GH secretion. Both MET and ISO increased GH mRNA content of cultured ovine pituitary cells. Somatostatin (10(-7) M) inhibited GHRH-stimulated GH secretion and GH mRNA accumulation. These results support the hypothesis that neurotransmitters may regulate or interact to further modulate pituitary hormone release. Moreover, the data indicate that neurotransmitters may not only regulate secretion but also regulate GH mRNA content and thus affect hormone synthesis.

Nonpeptidic inhibitors of human leukocyte elastase. 2. Design, synthesis, and in vitro activity of a series of 3-amino-6-arylopyridin-2-one trifluoromethyl ketones

A series of potent nonpeptidic inhibitors of the enzyme human leukocyte elastase (HLE) is reported. These inhibitors contain a 3-amino-2-pyridone ring as a central template in which the pyridone carbonyl and 3-position NH group are thought to form important hydrogen bonding interactions with the Val-216 residue of HLE. Substitution of the 6-position of the pyridone ring by various alkyl and aryl groups was found to afford increases in the in vitro potency of these inhibitors. A 6-position phenyl group, compound 10f, was found to result in a large increase in binding affinity, which was not obtained when the phenyl group was placed in either the 4- or 5-position of the molecule. Compound 10f was found to have good selectivity for HLE over other proteolytic enzymes, with the exception of bovine pancreatic chymotrypsin (BPC). Substitution of the 6-phenyl group in these molecules was found to decrease binding affinity for BPC without adversely affecting affinity for HLE.

Thermodynamics of hydrogen cyanide and hydrogen fluoride binding to cytochrome c peroxidase and its Asn-82-->Asp mutant

The thermodynamics of binding of fluoride and cyanide to cytochrome c peroxidase (CCP) and its Asn-82-->Asp mutant (D82CCP) in phosphate and acetate buffer at an ionic strength of 0.15 mol.kg-1 from pH 5.0 to 7.1 were investigated by titration calorimetry at 289 and 297 K. The binding reactions are enthalpically driven. The fluoride-binding constants determined from the titration calorimetry results were in agreement with those determined from difference-spectroscopy measurements. For cyanide binding to CCP at 297.9 K, the binding constant decreased from 8.95 (+/- 0.83) x 10(5) M-1 at pH 7.0 to 4.04(+/- 0.23) x 10(5) M-1 at pH 5.0, and the binding enthalpy increased from -57.2 +/- 1.4 kJ.mol-1 at pH 7.0 to -48.6 +/- 1.8 kJ.mol-1 at pH 5.0. For fluoride binding to CCP, the binding constant increased from 8.41(+/- 0.54) x 10(3) M-1 at pH 7.0 to 3.11(+/- 0.09) x 10(5) M-1 at pH 5.0 and the binding enthalpy increased from -71.9 +/- 1.1 kJ.mol-1 at pH 7.0 to -67.0 +/- 1.9 kJ.mol-1 at pH 5.0. The binding enthalpies for D82CCP were about the same as those for CCP. However, the binding constants for cyanide and fluoride to D82CCP were respectively a factor of two less and at least an order of magnitude less than the corresponding binding constants of CCP. Decreased ligand-binding strength in the D82CCP mutant is thus entirely due to entropic effects.

Respiratory distress following cesarean section: cryptic presentation of bladder injury

A case documenting the development of massive urinary ascites with associated pleural effusions and respiratory compromise due to an unrecognized cystotomy at the time of a tertiary low-vertical cesarean section is reported. The diagnosis was supported by elevated levels of serum blood urea nitrogen and creatinine and a peritoneal fluid to plasma creatinine ratio of 3:1. Imaging studies confirmed urinary extravasation into the peritoneum as well as bilateral pleural effusions and ascites. Primary intervention was to improve the patient's respiratory status and then to surgically repair the bladder wound.