Probing hydration contributions to the thermodynamics of ligand binding by proteins. Enthalpy and heat capacity changes of tacrolimus and rapamycin binding to FK506 binding protein in D2O and H2O

The stabilities of native proteins and protein-ligand complexes result from differential interactions among numerous polar and nonpolar atoms within the proteins and ligands and of these atoms with water. Delineation of the various energetic contributions of the stabilities of proteins or protein-ligand complexes in aqueous solution, and an evaluation of their structural basis, requires a direct account of the changes, in the interactions of the protein with the solvent, that accompany the folding or binding reactions. Two largely nonpolar, structurally related macrolide ligands, tacrolimus (also known as FK506) and rapamycin, each bind with high affinity to a common site on a small FK506 binding protein (FKBP-12) and inhibit its peptidylprolyl cis-trans-isomerase activity. In an effort to elucidate the influence of water on the thermodynamics of their binding reactions, we have measured the enthalpies of tacrolimus and rapamycin binding to FKBP-12, in buffered solutions of H2O (at pH 7.0) or D2O (at pD 7.0), by high-precision titration calorimetry in the temperature range 5-30 degrees C. For both tacrolimus and rapamycin binding, a large enthalpic destabilization of binding is observed in D2O relative to H2O, in the temperature range examined. Additionally, large negative constant pressure heat capacity changes are observed for the binding of the ligands in both H2O and D2O. A thermodynamic analysis is presented to identify the structural determinants of the differences in the energetics of binding in light and heavy water. The analysis suggests that a chief contributor to the observed enthalpic destabilization is the differential hydration, of protein and ligand atoms, by light and heavy water.

Transcriptional regulation of an endoglucanase and a cellodextrinase gene in Ruminococcus flavefaciens FD-1

A gene which encodes a 35 kDa protein with both carboxymethylcellulase and xylanase activity was cloned from Ruminococcus flavefaciens FD-1 and the nucleotide sequence determined. The FD-1 gene, celE, and the celA gene, which encodes a cellodextrinase, were used as probes to analyse transcription in R. flavefaciens grown under different conditions. Transcription of both genes was induced when cellulose was added to cells growing in cellobiose. This induction continued after cellulose depletion and after cell division had ceased. Transcription of both genes was also induced by cellotriose, although the effect was not as pronounced as induction by cellulose and was greater for the celA gene than for the celE gene.

In vivo and in vitro expression of octamer binding proteins in human melanoma metastases, brain tissue, and fibroblasts

The pattern of octamer sequence-specific DNA binding proteins expressed in human melanoma was examined in nuclear extracts of seven surgically-isolated tumors, short-term cultures of these tumors, and 25 human melanoma cell lines to determine the in vivo and in vitro distribution of the melanocytic-associated Oct-M1 and Oct-M2 octamer binding activities. In the biopsy tissue and cultured melanoma cells of a metastasis from the cerebellum, two other binding activities (N-Oct-2 and N-Oct-6) in addition to the Oct-M1, Oct-M2 and the generally expressed Oct-1 protein were detected; this profile was consistent with that seen in normal human and mouse brain tissue. Melanoma tissue removed from lymph nodes and cell lines established from them also showed Oct-1, Oct-M1, Oct-M2, and N-Oct-2. N-Oct-2 was distinguished from the comigrating Oct-2A activity by failure to react with Oct-2A-specific antibody. All but one of the 25 melanoma cell lines exhibited Oct-1, Oct-M1, and Oct-M2 and/or N-Oct-2 activity, whereas cultured normal melanocytes expressed only Oct-1 and Oct-M1. In contrast to murine fibroblasts, which express only Oct-1, human fibroblast strains also expressed Oct-2A binding activity, which was confirmed by reactivity with Oct-2A antibody and the presence of Oct-2A mRNA and indicated that Oct-2A has a more general role than that of a lymphoid-specific transcription factor. Overall, the results indicate that expression of neural-specific Oct factors in human melanoma is (1) aberrant compared with normal melanocytes, (2) can be modulated by the surrounding tissue in a brain metastasis, and (3) may be part of the altered program of differentiation accompanying transformation.

Contact sensitization to oxazolone: involvement of both interferon-gamma and interleukin-4 in oxazolone-specific Ig and T-cell responses

The synthesis and role of several lymphokines were examined during contact sensitization to oxazolone (OX). Application of OX to the skin of mice increased the delayed-type hypersensitivity (DTH) response to challenge, serum titres of OX-specific IgG1 and IgG2a, and draining lymph node cell (LNC) numbers. At day 3, LN contained detectable interleukin-4 (IL-4), interferon-gamma (IFN-gamma) and granulocyte-macrophage colony-stimulating factor (GM-CSF) but not IL-2 or IL-3 mRNAs; IL-3 and higher levels of IL-4, IFN-gamma and GM-CSF mRNAs were measured after 24 hr culture with anti-CD3 antibody in OX-primed but not unprimed LNC. As a result of sensitization, LNC secreted IL-3 constitutively and produced elevated levels of IL-2, IL-3, IL-4 and IFN-gamma in response to anti-CD3 antibody; a similar but weaker lymphokine response was recalled by OX-protein conjugate. CD4+ cells were the major source of the anti-CD3-induced lymphokines except IFN-gamma, which was derived mainly from CD8+ cells. Since both IL-4 and IFN-gamma were synthesized by OX-primed LNC in vivo and in vitro, their role was investigated by administering anti-lymphokine antibodies at the time of sensitization. Anti-IL-4 treatment reduced OX-specific serum IgG1 titres without affecting IgG2a titres, whereas anti-IFN-gamma treatment reduced IgG2a but not IgG1 titres. Although neither antibody altered DTH responsiveness, anti-IFN-gamma treatment markedly increased IL-4 production by CD4+ LNC and reduced IFN-gamma production in vitro, particularly by CD4+ cells. We conclude that endogenous IL-4 and IFN-gamma reciprocally influence the isotype of the Ig response to OX and that IFN-gamma also affects the relative levels of IL-4 and IFN-gamma synthesis by CD4+ LNC.

Thyroid abscess complicating subacute thyroiditis: a consequence of steroid therapy?

A patient with subacute thyroiditis developed a thyroid abscess after drainage of a pilonidal abscess. An infective focus in a patient with subacute thyroiditis on steroids should be treated aggressively with adequate antibiotic cover.

Thyroid function tests are rarely abnormal in patients with severe hyperemesis gravidarum

OBJECTIVES

There is considerable controversy in the literature as to the cause of hyperemesis gravidarum. The aim of this project was to measure a range of thyroid hormone levels in a group of hyperemetic pregnant women.

PATIENTS

The study was carried out in 10 first trimester pregnant women with hyperemesis gravidarum. All had been admitted to hospital due to the severity of their symptoms. Fifty age matched, healthy first trimester pregnant women were used as controls.

MEASUREMENTS

Blood samples from the women were analysed for total T3 (TT3), total T4 (TT4), free T4 (FT4), TSH, thyrotrophin receptor antibodies (TRAb), thyroid stimulating antibodies (TSAb) and thyroid microsomal and thyroglobulin antibodies. Human chorionic gonadotrophin (hCG) levels were also measured.

RESULTS

While individual patients were found to have some abnormal thyroid function tests the group as a whole showed no consistent pattern of abnormality and did not differ significantly from a group of healthy first trimester pregnant women. hCG levels were also within the normal range in the hyperemetic patients.

DISCUSSION

None of the women in this study received any antithyroid medication and their symptoms improved as the pregnancy progressed. These results would suggest that there is no underlying thyroid abnormality in patients with hyperemesis gravidarum. It would appear that neither thyroid hormones, nor hCG contribute to the pathogenesis of the condition.

Spin echo nuclear magnetic resonance studies on intact erythrocytes: changes in cellular metabolism as a consequence of carbimazole therapy

OBJECTIVE

Because the exact mechanism of action of carbimazole is uncertain, nuclear magnetic resonance (NMR) spectroscopy was used to investigate cellular changes in erythrocytes from Graves' patients following a course of carbimazole therapy.

DESIGN

NMR spectroscopy was carried out using intact erythrocytes obtained from Graves' patients prior to and at 2 and 12 months after carbimazole treatment. The data were correlated with thyroid hormone and antibody levels.

PATIENTS

Twenty patients (four males; 16 females) with newly diagnosed and previously untreated Graves' disease were enrolled into the study. Assessments were made prior to the commencement of therapy and after 2 and 12 months on treatment. Of the 20 patients assessed at 0 and 2 months only 12 completed the study.

MEASUREMENTS

The oxidation-reduction balance of erythrocyte glutathione was measured directly using 1H spin echo NMR spectroscopy of intact cells. Thyroid hormone and antibody levels were measured using reported methods.

RESULTS

At 2 and 12 months a significant (P < 0.01) oxidation of the erythrocyte glutathione was observed. Of the four thyroid related markers (T3, T4, TRAb and TSH) assessed in this study both T3 (P < 0.001) and TRAb (P < 0.001) were observed to correlate with the NMR observed changes in glutathione. However, in-vitro experiments indicated that carbimazole does not affect red cell glutathione directly.

CONCLUSIONS

A model is presented which uses the hydrated iodium cation (I+), the natural product of T4 conversion to T3, as a chemical oxidant which can produce the observed clinical alteration in intracellular glutathione in ex-vivo erythrocytes. It is suggested that a major factor in the action of carbimazole in Graves' disease may be to stimulate the function of the deiodinase enzymes.

Heat capacity changes and hydrophobic interactions in the binding of FK506 and rapamycin to the FK506 binding protein

Differential interactions among nonpolar moieties at protein/ligand interfaces, and of these nonpolar groups with water, collectively termed hydrophobic interactions, are widely believed to make important energetic contributions to the stability of protein/ligand complexes. Quantitative estimates of hydrophobic interactions, and an evaluation of their structural basis, are essential for obtaining structure-based predictions of the free energies of binding for the purpose of drug design. Two largely nonpolar, immunosuppressive agents, FK506 and rapamycin, each bind with high affinity to a common hydrophobic pocket on a small peptidylproline cis-trans isomerase known as FK506 binding protein (FKBP-12) and inhibit its activity. In an effort to elucidate the structural features of these ligands responsible for the observed energetics, we have undertaken an investigation of the thermodynamics of binding of FK506 and rapamycin to FKBP-12. Enthalpies of binding have been determined by high-precision titration calorimetry over a range of temperature, allowing estimates of heat capacity changes. By analyzing the distribution of changes in solvent-accessible surface area upon binding of FK506 to FKBP-12 from crystallographic data, it is found that 99% of the net surface buried upon binding involves nonpolar groups. This leads to a heat capacity change of FK506 binding, normalized to the amount of nonpolar surface, of -0.40 +/- 0.02 cal.K-1.mol-1.A-2 (1 cal = 4.18 J), a value similar to that obtained for the aqueous dissolution of hydrophobic substances. Our observations are discussed in view of the general nature of hydrophobic interaction processes.

Thermodynamics of ribonuclease T1 denaturation

Differential scanning calorimetry has been used to investigate the thermodynamics of denaturation of ribonuclease T1 as a function of pH over the pH range 2-10, and as a function of NaCl and MgCl2 concentration. At pH 7 in 30 mM PIPES buffer, the thermodynamic parameters are as follows: melting temperature, T1/2 = 48.9 +/- 0.1 degrees C; enthalpy change, delta H = 95.5 +/- 0.9 kcal mol-1; heat capacity change, delta Cp = 1.59 kcal mol-1 K-1; free energy change at 25 degrees C, delta G degrees (25 degrees C) = 5.6 kcal mol-1. Both T1/2 = 56.5 degrees C and delta H = 106.1 kcal mol-1 are maximal near pH 5. The conformational stability of ribonuclease T1 is increased by 3.0 kcal/mol in the presence of 0.6 M NaCl or 0.3 M MgCl2. This stabilization results mainly from the preferential binding of cations to the folded conformation of the protein. The estimates of the conformational stability of ribonuclease T1 from differential scanning calorimetry are shown to be in remarkably good agreement with estimates derived from an analysis of urea denaturation curves.

Solution structure of FK506 bound to FKBP-12

The complex of the immunosuppressant FK506 bound to FKBP-12 has been studied in solution using 1H and inverse-detected 13C NMR methods. The resonances of bound, 13C-labelled FK506 were assigned and a set of 66 intraligand NOE distance restraints were used to calculate the structure of the bound ligand by distance geometry and restrained molecular dynamics methods. The structure of bound FK506 in solution closely resembles that seen in the X-ray structure [17], except for the allyl region. The differences reflect the influence of intermolecular crystal contacts and have implications for interpretation of the interaction of the FK506/FKBP complex with its putative biological receptor.

Errors in young children's decisions about traffic gaps: experiments with roadside simulations

Young children's vulnerability as pedestrians has often been attributed to deficiencies in their decision making about vehicle approach times. Some studies have found a preponderance of risky decisions below the age of eight years. In contrast, studies using a closer simulation of road crossing, known as the pretend road, have found a preponderance of overcautious decisions in young children: traffic gaps of adequate size were frequently rejected (missed opportunities). However, the pretend road has potentially distorting characteristics which may account for this divergent pattern of findings. The experiments reported below show that new simulations that eradicate distortions nevertheless validate the pattern of results produced with the pretend road. Differences between adults and young children were pronounced for missed opportunities, but not for risky decisions. Subsidiary analyses suggest that the risky decisions of the youngest children may have arisen through lapses in attention, rather than deficits in timing. These findings run contrary to the view that attributes young children's pedestrian vulnerability to perceptuo-motor deficiency.

The Sulawesi Crested Black Macaque (Macaca nigra) menstrual cycle: changes in perineal tumescence and serum estradiol, progesterone, follicle-stimulating hormone, and luteinizing hormone levels

Events in the normal menstrual cycle of the endangered Sulawesi Crested Black Macaque (Macaca nigra) were characterized. Daily blood samples were obtained during 10 menstrual cycles from five M. nigra demonstrating regular cycles. The amount of perineal tumescence was scored daily. Serum levels of estradiol and progesterone were determined by RIA, serum LH levels were determined by the mouse Leydig cell bioassay, and serum FSH levels were determined by the rat granulosa cell aromatase bioassay. Cycle length was 39.8 +/- 1.0 days (mean +/- SEM) with an LH surge occurring 25 +/- 1.5 days from the onset of menses. After menses, both LH and estradiol were initially depressed, with estradiol first exceeding 50 pg/ml 8 days before the LH surge. In five cycles, peak estradiol levels (340 +/- 44 pg/ml) occurred on the day of the LH surge (637 +/- 58 ng/ml) and in the other five cycles, on the day before the LH surge. There was a broad increase of FSH in midcycle without a well-defined surge corresponding to the LH surge. Progesterone began increasing on the day of the LH surge and reached peak levels (6.8 +/- 0.96 ng/ml) 8 days later. Maximal perineal tumescence was generally associated with the time of the LH surge, but variation between animals made it impossible to predict accurately the day of the LH surge by perineal tumescence scores alone.

Investigation of the between-gel and within-gel variation in fragment size determinations found when using single locus DNA probes

Measurement variation in the sizing of DNA fragments has been assessed, examining within-gel and between-gel variability. Also, measurement variation detected between two different laboratories, using both manual and automated measurement techniques, has been investigated and discussed.

Structural rearrangements of the chloroplast genome provide an important phylogenetic link in ferns

The chloroplast genome of most land plants is highly conserved. In contrast, physical and gene mapping studies have revealed a highly rearranged chloroplast genome in species representing four families of ferns. In all four, there has been a rare duplication of the psbA gene and the order of the psbA, 16S, and 23S rRNA genes has been inverted. Our analysis shows that the described rearrangement results from a minimum of two inversions within the inverted repeat. This chloroplast DNA structure provides unambiguous evidence that phylogenetically links families of ferns once thought to belong to different major evolutionary lineages.

Immunological changes in normal pregnancy

During pregnancy the mother must tolerate intra-uterine allogenic fetal tissue. Failure of this tolerance may cause spontaneous abortion. The immunological changes occurring in normal pregnancy are poorly understood. The aim of this study was to investigate the immunological changes occurring in pregnancy. Thirty women in the first trimester; 10 in the second and 10 in the third trimester of pregnancy were studied and compared to age matched non-pregnant controls. In normal pregnancy there was an increase in the total white cell count with no change in the lymphocyte count. There was a fall in total T cell numbers and activated T cell numbers, with no change in helper/inducer or suppressor/cytotoxic T cell numbers. [3H]Thymidine uptake in response to three different mitogens was increased. This implies an increase in potential for the cells to respond to mitogens. There was no change in interleukin-2 receptor levels, suggesting that despite this increased potential there was no general activation of the immune system. A rise in IgM and IgG was found after mitogen stimulation of peripheral blood lymphocytes, suggesting an increase in potential antibody production. These results demonstrate that lymphocytes from pregnant women have an increased potential rather than an increased activity.

An analysis of the extracellular xylanases and cellulases of Butyrivibrio fibrisolvens H17c

The extracellular xylanase and cellulase components of Butyrivibrio fibrisolvens H17c were investigated. Two major peaks of enzyme activity were eluted by hydroxylapatite chromatography and designated complex A (CA), having cellulase activity, and complex B (CB) having predominantly xylanase activity but with some activity on carboxymethyl cellulose (CMC). CB was further purified on a DE-52 column and subjected to gel filtration. The xylanase and CMCase activities eluted in a single peak with an apparent molecular mass greater than thyroglobulin (Mr 669,000). CMC xymograms of polyacrylamide gels electrophoresed under non-denaturing conditions indicated the presence of five bands with CMCase activity from CA and eight from CB. Xylan xymograms under the same conditions indicated the presence of four bands of activity in CB. Under mild denaturing conditions the xylanase activity in CB was found in 11 bands with molecular mass ranging from 45 to 180 and the CMCase activity in three bands with molecular mass ranging from 45 kDa to 60 kDa. This indicates that CB exists as a multi-subunit protein aggregate of xylanases, some of which also have cellulase activity.

Children's perception of safety and danger on the road

This study investigates the ability of children between 5 and 11 years to select safe places to cross the street. The children were presented with situations which were either extremely safe or manifestly dangerous and were asked to correctly identify these. In other cases, they were asked to choose for themselves routes across the road which they thought would be safe. The tasks were presented in various ways: by means of a table-top simulation on which traffic scenarios had been contrived; by means of photographs of road situations; and by taking the children to real-world sites in the streets near their schools. All the experiments showed a similar pattern of results. Five- and 7-year-olds exhibited very poor skill in identifying dangerous road-crossing sites. Their judgments relied exclusively on the visible presence of cars in the vicinity. Other factors such as blind summits, obscuring obstacles or complex junctions were never recognized as threatening situations. They also showed an unwillingness to make detours when planning their own routes, even where the direct route was manifestly dangerous. Nine-year-olds showed a higher level of ability and 11-year-olds showed quite good skill in these judgements. No sex differences were apparent. These results suggest that young children up to about 9 years must often be at considerable risk as they do not have the ability to recognize a location as dangerous, even if they know the mechanics of the Green Cross Code. The implications for road safety education are discussed.

Children's perception of safety and danger on the road

This study investigates the ability of children between 5 and 11 years to select safe places to cross the street. The children were presented with situations which were either extremely safe or manifestly dangerous and were asked to correctly identify these. In other cases, they were asked to choose for themselves routes across the road which they thought would be safe. The tasks were presented in various ways: by means of a table-top simulation on which traffic scenarios had been contrived; by means of photographs of road situations; and by taking the children to real-world sites in the streets near their schools. All the experiments showed a similar pattern of results. Five- and 7-year-olds exhibited very poor skill in identifying dangerous road-crossing sites. Their judgments relied exclusively on the visible presence of cars in the vicinity. Other factors such as blind summits, obscuring obstacles or complex junctions were never recognized as threatening situations. They also showed an unwillingness to make detours when planning their own routes, even where the direct route was manifestly dangerous. Nine-year-olds showed a higher level of ability and 11-year-olds showed quite good skill in these judgements. No sex differences were apparent. These results suggest that young children up to about 9 years must often be at considerable risk as they do not have the ability to recognize a location as dangerous, even if they know the mechanics of the Green Cross Code. The implications for road safety education are discussed.

Changes in immunologic parameters in normal pregnancy and spontaneous abortion

To study the immunologic characteristics of miscarriage, 40 nonpregnant control subjects, 40 primigravid women in the first trimester of pregnancy, and 18 patients admitted with a spontaneous abortion were investigated. The total white blood cell count was raised significantly in normal pregnancy and spontaneous abortion (p less than 0.0005). The lymphocyte count was unchanged. The total T-cell number fell significantly in normal pregnancy and abortion (p less than 0.01). No change was seen in the cytotoxic suppressor or helper/inducer T-cell numbers. The number of activated T cells fell significantly in both groups of patients (p less than 0.0005). The response to mitogens was greatly increased in both normal patients and those with miscarriage. A marked rise in interleukin-2 receptor levels was noted in patients with spontaneous abortion (p less than 0.005). The changes in white blood cell count, total T-cell number, activated T-cell number, and mitogen activity were thought to be a direct result of pregnancy. The rise in interleukin-2 receptor levels was seen only in the miscarriage group. Although it is not known if these changes are cause or effect, it would appear that immunologic abnormalities are associated with spontaneous abortion.

Heterogeneity in lymphokine profiles of CD4+ and CD8+ T cells and clones activated in vivo and in vitro

Analysis of lymphokine mRNA expression and protein secretion by about 100 short-term alloreactive T-cell clones revealed marked heterogeneity in the combinations of lymphokines synthesized. This finding argues against a simple model in which T cells express either an unrestricted (Th0) or a restricted (Th1 or Th2) lymphokine profile. Lymphokine titers appeared to be normally distributed, with the percentage of positive clones for any one product determined by the threshold of detection. Accordingly, the observation that CD4+ clones on average produced higher titers of most lymphokines than CD8+ clones indicated that apparent differences between the lymphokine profiles of these two subsets were quantitative rather than qualitative. Patterns of lymphokine gene expression detected in whole tissues or by analysis of single cells and clones were markedly influenced by in vivo priming. Relative levels of expression of IL-4, IFN-gamma and GM-CSF in lymphoid tissues differed in mice undergoing a GvHR or following contact sensitization with OX or immunization with KLH in adjuvant. Consistent with the finding that IL-4 was the major lymphokine mRNA detected in lymph nodes of KLH-primed mice, most short-term KLH-specific clones derived from such mice also expressed IL-4. A similar approach to the detection of lymphokine-secreting T-cell precursors activated late in L. major infection showed that most clones from the L. major-resistant strain, C57BL/6, secreted IFN-gamma without IL-4 whereas most clones from the susceptible strain, BALB/c, secreted IL-4 without IFN-gamma. Differences were also noted in anti-CD3-induced IL-3 production at the single-cell level between CD8+ cells activated in the GvHR or against a tumor allograft. Con A-induced, filler cell-dependent cloning of CD4+ T cells from unprimed mice gave rise both to IFN-gamma-producing and to IL-4-producing clones. A requirement for an undefined, filler cell-dependent signal for development of IL-4-secreting clones was suggested by the finding that clones of normal CD4+ and CD8+ T cells activated in an anti-CD3-induced, filler cell-free system exclusively produced IFN-gamma and IL-3 without detectable IL-4 or IL-6. With a view to developing a single-cell approach to the analysis of lymphokine profiles of in vivo-activated T cells, sensitive assays for IL-3 and other lymphokines were used to measure secreting cells activated in the GvHR or against a tumor allograft.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical analysis in intact erythrocytes using 1H spin echo NMR

A new method of clinical analysis based on 1H spin echo NMR spectroscopy is presented. It is capable of providing information on six metabolites within viable erythrocytes, directly and without any preparative procedures prior to analysis except for cell separation and washing. Erythrocytes from patients with rheumatoid arthritis and Graves' disease are compared with cells obtained from healthy volunteers. The NMR detectable species in the cytosol of the cells are glutathione, ergothioneine, choline, creatine, glycine, lactate and to a lesser extent alanine and valine. Significant differences are observed between the ergothioneine pools in the rheumatoid group (P less than 0.01) compared to the control group. The glutathione: di-glutathione ratio can be assessed from the ratio, g2 to g4, taken from different signals in the glutathione molecule. The total concentration of glutathione present is easily assessed qualitatively but is more difficult to quantitate.

Cloning, sequencing and expression of a gene encoding a 73 kDa xylanase enzyme from the rumen anaerobe Butyrivibrio fibrisolvens H17c

The cloning, expression and nucleotide sequence of a 3 kb DNA segment on pLS206 containing a xylanase gene (xynB) from Butyrivibrio fibrisolvens H17c was investigated. The open reading frame (ORF) of 1905 bp encoded a xylanase of 635 amino acid residues (Mr 73156). At least 850 bp at the 3' end of the gene could be deleted without loss of xylanase activity. The deduced amino acid sequence was confirmed by purifying the enzyme and subjecting it to N-terminal amino acid sequence analysis. In Escherichia coli C600 (pLS206) cells the xylanase was localized in the cytoplasm. Its optimum pH for activity was between pH 5.4 and 6, and optimum temperature 55 degrees C. The primary structure of the xylanase showed a significant level of identity with a cellobiohydrolase/endoglucanase of Caldocellum saccharolyticum, as well as with the xylanases of the alkaliphilic Bacillus sp. strain C-125, B. fibrisolvens strain 49, and Pseudomonas fluorescens subsp. cellulosa.

Angiotensin II as a potential method of targeting cytotoxic-loaded microspheres in patients with colorectal liver metastases

Regional chemotherapy is commonly used to treat patients with colorectal liver metastases. However, improvement in survival has still not been demonstrated. Cytotoxic loaded albumin microspheres for arterial administration have been described as a means of improving the the therapeutic index, but their distribution depends upon the prevailing pattern of arterial blood-flow at the time of injection. In this study, the ability of the vasoactive drug angiotensin II to target arterially injected microspheres to colorectal liver metastases is assessed in nine patients using scintigraphic planar and tomographic imaging. The median tumour: normal ratio in nine patients with colorectal liver metastases was 3.4:1 before the administration of angiotensin II. The corresponding ratio after administration of angiotensin II was 7.3:1. The median improvement factor was 1.8 (P less than 0.05). The data suggest that worthwhile tumour targeting can be achieved with angiotensin II in patients with colorectal liver metastases.

Solution structure of the major binding protein for the immunosuppressant FK506

The major FK506 binding protein (FKBP, relative molecular mass approximately 11,800; Mr 11.8K) and cyclophilin (Mr approximately 17K) belong to a class of proteins termed immunophilins. Although unrelated at the amino-acid sequence level, they both possess peptidyl-prolyl cis-trans isomerase activities which are inhibited by immunosuppressants that block signal transduction pathways leading to T-lymphocyte activation. FK506 and rapamycin strongly inhibit the peptidyl-prolyl cis-trans isomerase activity of FKBP, whereas cyclosporin A inhibits that of cyclophilin. The significance of this enzyme activity and the role of the immunophilins in immunoregulation is unknown. To understand better the function of the immunophilins and their interaction with inhibitors, we are investigating the solution structures of FKBP and FKBP-inhibitor complexes by multidimensional NMR methods. Here we report the solution conformation of FKBP, as generated by NMR, distance geometry and molecular dynamics methods. The regular secondary structure of FKBP is composed mainly of beta sheet (approximately 35%) with little helical structure (less than 10%). The hydrophobic core of the molecule, containing the buried side chains of six of the protein's nine aromatic amino acids, is enclosed by a five-stranded antiparallel beta sheet on one side, a loop and a short helix at residues 51-56 and 57-65, and an aperiodic loop at residues 81-95. Examination of the structure suggests a possible site of interaction with FK506.

Examination of phenylalanine microenvironments in proteins by second-derivative absorption spectroscopy

We have employed near ultraviolet derivative absorption spectroscopy to study the microenvironments of phenylalanine residues in proteins. The use of second-derivative uv spectra in the 250- to 270-nm range effectively suppresses spectral contributions from tryptophan and tyrosine residues. Fitting a polynomial to the numerically calculated second-derivative spectrum allows precise determination of the position of the negative derivative peak near 258 nm. This position is shown to be correlated with the polarity of the microenvironments of phenylalanine residues. This approach allows monitoring of changes in the state of phenylalanine side chains during folding/unfolding of the proteins. In addition, this method permits perturbation of protein samples with ethylene glycol to be used to establish the relative degree of solvent exposure of protein phenylalanine.

The effect of lithium therapy on parameters thought to be involved in the development of autoimmune thyroid disease

This study has considered the effects of primary affective disorders and lithium therapy on a number of factors thought to be important in the development of autoimmune thyroid disease. These factors were examined in (a) controls with no history of any such disorders; (b) patients with primary affective disorders treated with drugs other than lithium and (c) patients with primary affective disorders treated with lithium alone. Eight of 40 patients who were receiving lithium therapy were found to be positive for thyroid microsomal and/or thyroglobulin antibodies, compared to only 3/40 patients who were receiving some other form of treatment for their depression. Peripheral blood mononuclear cells from patients receiving lithium were found to have significantly reduced numbers of suppressor/cytotoxic T cells (P less than 0.05). In addition, suppressor T cells from these patients showed a significantly reduced response to stimulation with concanavalin A (P less than 0.01). These effects were greatest in patients found to be antibody positive. Increased B cell activity, as measured by increased IgG and IgM release following mitogen stimulation, was seen in patients receiving lithium and in those patients receiving other forms of treatment for their depression. This would suggest that the increase is a feature of primary affective disorders and is not due specifically to lithium treatment. It would appear from this study that lithium therapy induces antibody formation in susceptible individuals and this may ultimately lead to the development of thyroid disease.

In vivo and in vitro studies into the immunological changes following iodine 131 therapy for Graves' disease

Radio-iodine therapy for Graves' disease is followed by immunological changes in addition to effects on thyroid hormone production. The present study examined these changes and the mechanisms responsible for them. Of the 15 patients enrolled in the study, 10 became hypothyroid in the first year after iodine 131 therapy. Patients who became hypothyroid had a tendency to show a rise in serum thyrotropin receptor antibody levels (30 +/- 14 to 40 +/- 9 units; NS) and a significant rise in immunoglobulin production (324 +/- 153 to 740 +/- 200 ng/ml; P less than 0.0005) from mitogen-stimulated peripheral blood lymphocytes (a measure of B-cell activity) 2 months after iodine 131 therapy. The increases were not seen in the patients who remained euthyroid at 1 year. In vitro studies suggested that the rise in B-cell activity is due to a fall in suppressor T cell numbers, a change shown to occur following iodine 131 therapy in previous studies. Our results indicate that immunological changes do arise after iodine 131 therapy for Graves' disease but appear to be confined to patients who subsequently became hypothyroid. It is not possible from this study to determine whether the immunological changes appear as a consequence of thyroidal destruction leading to hypothyroidism or whether they contribute directly to it.

Arteriovenous shunting in patients with colorectal liver metastases

The outlook for patients with colorectal liver metastases is poor. Microspheres have been combined with cytotoxics and administered via the hepatic artery in an attempt to improve tumour drug exposure within the liver. However, it has been suggested that arteriovenous connections might occur in association with intrahepatic tumours causing loss of regional advantage, and that the administration of microspheres further exacerbates arteriovenous shunting. In seven patients with colorectal liver metastases, base-line shunting was measured using a tracer quantity of radio-labelled albumin microspheres. The shunted fraction of a 'therapeutic quantity' of microspheres was subsequently measured in the same group of patients using albumin microspheres carrying a different radio-label. Base-line shunt for 0.5 x 10(6) microspheres was found to be 2.2 +/- 1.8% (mean +/- s.d.); the percentage shunt of a therapeutic quantity (40-80 x 10(6)) of microspheres was 3.0 +/- 0.8%. We conclude that arteriovenous shunting in patients with colorectal liver metastases is minimal, and is not significantly increased by the administration of therapeutic quantity of microspheres during regional chemotherapy.

The incidence of clinical thyroid dysfunction in an unselected group of pregnant and post partum women

This study has examined the incidence of thyroid dysfunction during pregnancy and up to six months post partum in 65 women attending an antenatal clinic in the West of Scotland. Five were found to be positive for thyroid antibodies at presentation and in these the antibody titre fluctuated during pregnancy and in the post partum period. One patient developed thyroglobulin antibodies post partum. Mean total T3 and total T4 levels rose during pregnancy but had normalised by six weeks post partum. The changes in FT4 and TBG levels observed during pregnancy did not normalise until after six weeks post partum. Only one patient developed any biochemical evidence of thyrotoxicosis post partum and this was not found to be associated with the presence of thyroid antibodies. No patient showed any evidence of hypothyroidism.

The effect of pre-operative potassium iodide therapy on antibody production

Previous studies have suggested that iodide may increase the incidence of thyroid disease and anti-thyroid antibodies in predisposed individuals. This study has considered the effects of pre-operative potassium iodide (60 mg twice daily, for 10 days) on the immune system of patients with Graves' disease. The treatment regimen used maintained all patients in a clinically and biochemically euthyroid state prior to surgery. Potassium iodide significantly increased serum thyrotropin receptor antibody levels and B cell activity as determined by increased immunoglobulin production from mitogen stimulated peripheral blood lymphocytes. These effects were not observed in the two control groups of Graves' disease patients. Our in vivo findings would support previous in vitro work showing that potassium iodide does act on the immune system and this may be the mechanism by which iodide induces thyroid dysfunction in predisposed individuals.

Cloning, sequencing and analysis of expression of a Butyrivibrio fibrisolvens gene encoding a beta-glucosidase

The cloning, expression and nucleotide sequence of a 3.74 kb DNA segment on pLS215 containing a beta-glucosidase gene (bglA) from Butyrivibrio fibrisolvens H17c was investigated. The B. fibrisolvens bglA open reading frame (ORF) of 2490 bp encoded a beta-glucosidase of 830 amino acid residues with a calculated Mr of 91,800. In Escherichia coli C600(pLS215) cells the beta-glucosidase was localized in the cytoplasm and these cells produced an additional protein with an apparent Mr of approximately 94,000. The bglA gene was expressed from its own regulatory region in E. coli and a single mRNA initiation point was identified upstream of the bglA ORF and adjacent to a promoter consensus sequence. The primary structure of the beta-glucosidase showed greater than 40% similarity with a domain of 237 amino acids present in the beta-glucosidases of Kluyveromyces fragilis and Clostridium thermocellum. The B. fibrisolvens beta-glucosidase hydrolysed cellobiose to a limited extent, cellotriose to cellobiose and glucose, and cellotetraose and cellopentaose to predominantly glucose.

Nucleotide sequence of the celA gene encoding a cellodextrinase of Ruminococcus flavefaciens FD-1

The nucleotide sequence of a 3.6 kb DNA fragment containing a cellodextrinase gene (celA) from Ruminococcus flavefaciens FD-1 was determined. The gene was expressed from its own regulatory region in Escherichia coli and a putative consensus promoter sequence was identified upstream of a ribosome binding site and a TTG start codon. The complete amino acid sequence of the CelA enzyme (352 residues) was deduced and showed no significant homology to cellulases from other organisms. Two lysozyme-type active sites were found in the amino-terminal third of the enzyme. In E. coli the cloned Cel A protein was translocated into the periplasm. The lack of a typical signal sequence, and the results of transposon phoA mutagenesis experiments indicated that CelA is secreted by a mechanism other than a leader peptide.

The effects of antithyroid drugs on intercellular mediators

The antithyroid drugs methimazole and propylthiouracil have been shown to affect the function of monocytes and B and T lymphocytes in vitro. The aim of this study was to investigate the mechanism responsible for signalling between these various cell types. Propranolol, a drug known to have no effect on the immune system, was also included as a control against which the effects of the other drugs could be monitored. Peripheral blood lymphocytes from control subjects were stimulated with phytohemagglutinin in the presence or absence of antithyroid drugs. Propranolol was found significantly to inhibit beta 2 microglobulin production. In addition it was also found to be a very weak scavenger of free oxygen radicals. Methimazole significantly increased interleukin 2 levels (p less than 0.01), but had no significant effect on either gamma-interferon or beta 2 microglobulin production. Propylthiouracil also increased interleukin 2 levels (p less than 0.001) and significantly decreased beta 2 microglobulin production (p less than 0.01). Both drugs were found to be scavengers of free O2 radicals. It would appear that IL-2 is involved in intercellular signalling and this process may involve free radicals.

A dynamic quaternary structure of bovine alpha-crystallin as indicated from intermolecular exchange of subunits

The structural bovine eye lens protein alpha-crystallin was dissociated in 7 M urea and its four subunits, A1, A2, B1, and B2, were separated by means of ion-exchange chromatography. Homopolymeric reaggregates of these subunits were prepared by removal of the denaturant via dialysis. It was found that subunits were exchanged upon incubation of mixtures of two homopolymers under native conditions. New hybrid species were formed within 24 h as demonstrated by isoelectric focusing. Moreover, native alpha-crystallin molecules also exchanged subunits when incubated with homopolymeric aggregates of B2 subunits. Subunit exchange between native alpha-crystallin molecules is postulated, and a "dynamic quaternary structure" is presented that allows the polydisperse protein to adapt to changes in cytoplasmic conditions upon aging of the lens tissue.

Ophthalmopathy in early thyrotoxicosis--relationship to thyroid receptor antibodies and effects of treatment

A prospective study of 25 newly diagnosed thyrotoxic patients was undertaken to determine the incidence and severity of ophthalmopathy in the early stages of the disease. A quantitative analysis of the ocular muscle changes was made using B scan ultrasonography, and the effects of treatment for the thyroid disease on the course of the eye changes was assessed. Although the majority (75%) of patients showed only mild clinical signs of ophthalmopathy (Werner Class 3 or less), 92% had ultrasonographic evidence of ocular muscle enlargement. Clinical involvement of the extraocular muscles was seen in 12% of the cases. There was an inverse correlation between the serum level of thyroid stimulating hormone receptor antibody (TR Ab) and the size of the extraocular muscles. Recovery of the euthyroid state with treatment was accompanied by a decrease in orbital infiltration in some cases, both clinically (reduced amplitude of intraocular pressure rise on elevation of the globe) and by ultrasonography, but the improvement was not statistically significant.

Inhibition of alpha-crystallin aggregation by gamma-crystallin

The transparency of the mammalian lens is primarily maintained by short range order among the major proteins of the lens fiber cells, the crystallins. Although these proteins are highly conserved at the amino acid sequence level, it has proven difficult to establish that they possess other than structural functions. We find that when non-lens proteins are added to concentrated solutions of alpha-crystallin, aggregation is induced, presumably through excluded volume effects. In contrast, the monomeric gamma-crystallins and the low molecular weight form of beta-crystallin (beta L) cause a decrease in the size of alpha-crystallin. When the naturally aggregated form of alpha-crystallin is examined, gamma- and beta L-crystallin, as well as a reducing agent, also cause partial dissociation as detected by dynamic light scattering and size exclusion chromatography, while no effect is seen with non-crystallin proteins. Furthermore, the chemical cross-linking of alpha-crystallin is inhibited by gamma- and beta L-crystallin but not by other proteins. The ability of gamma-crystallin to inhibit the association of alpha-crystallin is primarily localized to the gamma-II form which contains a high degree of exposed thiols. Only small amounts of gamma- and beta L-crystallin, however, can be cross-linked to alpha-crystallin in mixtures of the three proteins even at very high protein concentrations. These results suggest that one possible role for the lower molecular weight crystallins may be to minimize through a reductive effect the intrinsic tendency of alpha-crystallin to aggregate, an association reaction implicated in the loss of lens transparency.

pH dependence of the urea and guanidine hydrochloride denaturation of ribonuclease A and ribonuclease T1

To investigate the pH dependence of the conformational stability of ribonucleases A and T1, urea and guanidine hydrochloride denaturation curves have been determined over the pH range 2-10. The maximum conformational stability of both proteins is about 9 kcal/mol and occurs near pH 4.5 for ribonuclease T1 and between pH 7 and 9 for ribonuclease A. The pH dependence suggests that electrostatic interactions among the charged groups make a relatively small contribution to the conformational stability of these proteins. The dependence of delta G on urea concentration increases from about 1200 cal mol-1 M-1 at high pH to about 2400 cal mol-1 M-1 at low pH for ribonuclease A. This suggests that the unfolded conformations of RNase A become more accessible to urea as the net charge on the molecule increases. For RNase T1, the dependence of delta G on urea concentration is minimal near pH 6 and increases at both higher and lower pH. An analysis of information of this type for several proteins in terms of a model developed by Tanford [Tanford, C. (1964) J. Am. Chem. Soc. 86, 2050-2059] suggests that the unfolded states of proteins in urea and GdnHCl solutions may differ significantly in the extent of their interaction with denaturants. Thus, the conformations assumed by unfolded proteins may depend to at least some extent on the amino acid sequence of the protein.

An evaluation of human chorionic gonadotrophin (HCG) therapy in boys with delayed puberty

Fifty male patients with delayed pubertal development (chronological age 13.3-17.6 years; bone age 9.5-14 years) were treated with human chorionic gonadotrophin (HCG) 1500-2000 units twice weekly for six months to promote pubertal development and accelerate growth. Response was compared with an untreated control group of 28 patients (chronological age 12.5-17.5 years; bone age 7.0-13.0 years). Forty-four of 46 patients in the treatment group achieved genital stage 3 or 4 by the end of therapy; untreated patients either remained unchanged or advanced only one genital stage during this period. Testicular volumes increased from a median 4.5 ml (range 1-12 ml) to 9 ml (range 3.5-15 ml) in the treated patients. In untreated patients testicular volume increased from 6.0 ml (range 2-10 ml) to 9.5 ml (range 4-20 ml) over the same period. In patients initially growing at less than 7.0 cm/year height velocity increased from 3.9 cm/year (range 0-6.6 cm/year) to 12.7 cm/year (range 8.9-16.8 cm/year) during therapy, falling to 6.0 cm/year (range 0-12 cm/year) in the three-month period immediately following treatment. Patients initially growing at greater than 7.0 cm/year showed variable responses to treatment. Prepubertal patients showed the greatest acceleration in annual growth compared with controls. Treated patients with an initial skeletal age less than 12.0 years showed either a final height (when known) which was less than initially predicted or a significant reduction in predicted height following treatment. Skeletal age greater than 12.0 years was not associated with excess osseous maturation. In conclusion, pre-pubertal children growing at less than 7 cm/year show the greatest benefit from HCG therapy, but final height may be prejudiced if initial bone age is less than 12 years.

Thyrotropin receptor antibodies associated with post-operative relapse of thyrotoxicosis in a pregnancy complicated by neonatal thyrotoxicosis

This case describes the clinical, biochemical and immunological features associated with relapse of thyrotoxicosis during pregnancy in a patient who had recently undergone a subtotal thyroidectomy for Graves' disease. The baby, shortly after birth, showed clinical and biochemical features of thyrotoxicosis which responded to carbimazole therapy. Thyrotropin receptor antibodies and thyroid stimulating antibodies were present in the blood of the mother and baby. The clinical course of the neonatal thyrotoxicosis correlated with the TSH receptor antibody levels.

Free radical activity in type 2 diabetes

Free radical activity has been implicated in the development of diabetic vascular complications in Type 1 diabetes. The aim of the present study was to investigate the levels of free radical scavengers, particularly erythrocyte superoxide dismutase, plasma and erythrocyte lysate thiol, and caeruloplasmin in 22 Type 2 diabetic patients clinically free of complications, and 15 comparable non-diabetic control subjects. The concentration (median (range] of both superoxide dismutase (23 (10-39) vs 45 (25-75) mumol l-1; p less than 0.001) and plasma thiol (374 (172-523) vs 460 (386-595) mumol l-1; p less than 0.01) were reduced in the diabetic group. There were no significant differences in the concentration of erythrocyte lysate thiol (199 (114-520) vs 188 (114-328) mumol l-1) or plasma caeruloplasmin (18 (9-31) vs 24 (6-50) mumol l-1) between the groups. This reduction in superoxide dismutase and the imbalance in the redox status of the plasma and lysate thiol demonstrated is consistent with an increase in free radical activity in Type 2 diabetes.

The effect of carbimazole therapy on interleukin 2, interleukin 2 receptors and free radicals

Levels of Interleukin 2 (IL2), IL2 receptors (IL2R) and free radical scavengers were measured in 25 Graves' disease patients prior to and following an 8 week course of Carbimazole therapy in an attempt to understand the mechanism by which the drug acts on the immune system. In untreated Graves' patients IL2R levels were elevated and IL2 levels reduced. Free radical scavengers were also reduced in these patients. Following treatment IL2R levels fell and IL2 levels rose. Levels of the free radical scanvengers also rose. It is not clear whether it is the fall in IL2R levels or the rise in the level of free radical scavengers (implying a reduction in free radical activity) which is responsible for the rise in IL2.

The behaviour of suppressor-inducer T cells following treatment for Graves' disease

The expression of surface markers of T cell subsets in the peripheral blood of 30 Graves' disease patients was investigated pre and post therapy using two colour flow cytometry. Reduced numbers of total, helper/inducer and suppressor/cytotoxic T cells were found in untreated Graves' patients. Numbers of suppressor-inducer T cells which are associated with maintaining the normal immune response, did not differ significantly between untreated Graves' patients and controls. Although 8 weeks' Carbimazole therapy reversed the changes in total, helper/inducer and suppressor/cytotoxic T cells, PTU or 131I therapy did not. While suppressor-inducer T cell numbers were not affected by Carbimazole or PTU therapy, 131I treatment caused a decrease in suppressor-inducer T cell numbers.

A differential scanning calorimetric study of the bovine lens crystallins

Differential scanning calorimetry was performed on the five major lens crystallin fractions [HM-alpha, alpha, beta H, beta L, and (beta s + gamma)] of the bovine lens as well as on more purified forms of alpha- and gamma-crystallins. All were found to be relatively thermally stable although the alpha-crystallin were found to at least partially unfold at an approximately 10 degrees C lower temperature than the beta and gamma fractions. Increasing protein concentration had little effect on gamma-crystallin thermograms but had marked effects on those of the alpha- and beta-crystallins. Increases in the thermal stability with increasing protein concentration for the beta-crystallins can be explained most simply by the known beta L/beta H equilibrium, but, in the case of the alpha-crystallins, excluded volume effects may be an important factor. In both cases, the increased stability at high concentrations could be of physiological relevance. As well as the expected endothermic unfolding transitions, all of the lens crystallins revealed exothermic peaks that correlate with protein precipitation. Interestingly, this phenomenon occurs only after extensive structural alteration in the case of the alpha-crystallins but is present very early in the initial stages of structural perturbation of the beta- and gamma-crystallins.

The prognostic value of TSH receptor binding and thyroid stimulating antibodies following antithyroid drug treatment of Graves' disease

Following a course of medical therapy for Graves' disease approximately 50% of patients relapse. Previous studies have tried to identify these patients by measuring antibodies to the TSH receptor using a range of assay methods. Such studies have produced widely discrepant results. The aim of the present study was to compare the accuracy with which TSH receptor binding antibodies and thyroid-stimulating antibodies could identify cases of relapse and remission. Fifty-six newly diagnosed and previously untreated Graves' disease patients were recruited into the study. At presentation 4 were negative for TSH receptor antibody and 5 negative for TS-ab. The remaining 47 were positive for TSH receptor antibody and TS-ab although correlation of the degree of abnormality between methods was poor (r = 0.13 NS). After 12 months carbimazole treatment 28 patients relapsed during the following year and 19 remained in remission. TSH receptor antibody levels obtained at the end of a 12-month course of treatment correctly identified 93% who relapsed and 95% who remained in remission. TS-ab levels could only correctly identify 68% who relapsed and 53% who remained in remission. These results have shown that the accuracy with which patients likely to relapse can be identified depends on the assay method chosen which may account for some of the discrepancies found in previously published studies.