Population Pharmacokinetics of Selumetinib and Its Metabolite N-desmethyl-selumetinib in Adult Patients With Advanced Solid Tumors and Children With Low-Grade Gliomas

Selumetinib (AZD6244, ARRY‐142886), a mitogen activated protein kinases (MEK1 and 2) inhibitor, has been granted orphan drug designation for differentiated thyroid cancer. The primary aim of this analysis was to characterize the population pharmacokinetics of selumetinib and its active metabolite N‐desmethyl‐selumetinib in patients with cancer. Concentration–time data from adult and pediatric clinical trials were pooled to develop a population pharmacokinetic model using a sequential approach where selumetinib and N‐desmethyl‐selumetinib data were modeled separately. A sequential zero‐ and first‐order absorption with lag time with a two‐compartment model for selumetinib and a two‐compartment model for N‐desmethyl‐selumetinib best described the concentration–time data. Intrapatient variability in absorption was higher than interpatient variability. The apparent drug clearance (CL/F) from the central compartment was 13.5 L/hr (RSE 4.9%). Significant covariates for CL/F were age, alanine aminotransferase, and body surface area. This study confirms that flat dosing is appropriate in adults, whereas body‐surface area based dosing should be used in pediatric patients.

Genotyping spring viraemia of carp virus and other piscine vesiculo-like viruses using reverse hybridisation

A simple nylon membrane-based DNA macroarray was developed to genotype spring viraemia of carp virus (SVCV) and related viruses. Twenty-six viruses were genotyped using the array, and the results were confirmed by phylogenetic analysis of a 426 bp partial glycoprotein gene sequence. The array was not only capable of discriminating between the 4 main genogroups of cyprinid vesiculo-type viruses described previously, but also accurately sub-type the SVC viruses assigned to Genogroup I. The assay offers a practical solution for diagnostic laboratories that currently lack a sequencing capability to confirm the nature of PCR products generated in suspected SVCV cases.

Efficacy of an internet-based behavioral weight loss program for overweight adolescent African-American girls

OBJECTIVE

This randomized controlled trial tested the efficacy of an internet-based lifestyle behavior modification program for weight management in African-American girls.

DESIGN

African-American girls were randomly assigned to an interactive behavioral internet program or an internet health education program, the control condition. The behavioral intervention included internet counseling and was highly interactive. The control intervention was a passive (non-interactive) educational program. Parents were also participants in the study. Participants in both treatment groups met in face-to-face sessions on four occasions over the first 12 weeks of a 6-month intervention.

SUBJECTS

The study enrolled 57 African-American adolescent girls (ages 11 to 15 years) who were overweight or obese and had at least one biological parent who was obese [body mass index (BMI) >30 kg/m2]. Of the 57 participants, 50 (88%) completed the 6-month trial.

MEASUREMENTS

Outcome data, including BMI, body weight, body composition, dietary intake, and weight loss behaviors were collected at baseline and 6-months later. A computer server tracked utilization of the websites. Participation in the program was measured by number of "hits" on the website.

RESULTS

Compared to the control condition, adolescents in the behavioral treatment lost more body fat (group difference =1.6% body fat) and parents lost significantly more body weight (group difference =2.1 kg). Utilization of the behavioral website by adolescents and parents was associated with positive outcome. Dietary fat intake was lowered for adolescents and parents in the behavioral treatment group.

CONCLUSION

An internet-based behavioral intervention was superior to internet-based health education and yielded decreased body fat for adolescent girls and decreased body weight for parents.

Structure of a bovine thrombin-hirudin51-65 complex determined by a combination of molecular replacement and graphics. Incorporation of known structural information in molecular replacement

Crystals of the bovine thrombin-hirudins(51-65) complex have space group P6(1)22 with cell constants a = 116.4, and c = 200.6 A and two thrombin molecules in the asymmetric unit. Only one thrombin molecule could be located by generalized molecular replacement; the second was fit visually as a rigid body to an improved electron-density difference map. The structure was refined to R = 0.192 with two B values per residue (main chain and side chain) at 3.2 A. The polar interactions of the peptides with the exosite of thrombin show differences consistent with the known flexibility in the interactions of the C-terminal peptide of hirudin with thrombin. The hirudin peptide in complex 2 has a higher temperature factor as compared with peptide 1 which may be correlated partly with a larger number of short-range electrostatic interactions between peptide 1 and thrombin and partly with the fact that thrombin 2 is epsilon-thrombin which is cleaved at Thr149A near the peptide binding site. Later, using this structure as a test case, it was shown that the position for the second thrombin could also be determined by a novel modification of the molecular-replacement method in which the contribution of the known molecule is subtracted from the structure factors. This approach is facile and applicable to any crystal containing two or more macromolecules in the asymmetric unit in which some but not all of the molecules can be determined by molecular replacement.

Crystallization of hemoglobins II and III of the symbiont-harboring clam Lucina pectinata

Diffraction data to 2.7 A resolution were measured on crystals of the homotetramers of components II and III of the cytoplasmic hemoglobin of the symbiont-harboring clam Lucina pectinata. Even though the crystallization conditions are different and the sequence homology of the two hemoglobins is only 63%, the crystals are isomorphous to each other and to the heterotetramer Hb II/III, implying that the residues primarily involved in the intermolecular interactions and responsible for crystal cohesion may be invariant.

Comparison of extraction of a β-blocker from plasma onto a molecularly imprinted polymer with liquid–liquid extraction and solid phase extraction methods

An optimised solid phase extraction (SPE) method developed for the extraction of a structural analogue of the beta-blocking drug propranolol from plasma utilising a molecularly imprinted polymer (MIP) has been compared with methods based on conventional liquid-liquid extraction (LLE), and SPE using C18-bonded and immobilised phenyl boronic acid (PBA). All four methods could be used for the extraction of the analyte with acceptable accuracy and precision. The MIP-based method, unlike the other methods required a protein precipitation step prior to extraction to eliminate the effects of co-extracted protein. The best performance was seen with the LLE method followed by SPE on the C18 phase. The MIP-based method represented no advantage over the comparator methods for this analyte. Indeed the performance of the MIP-based method was marginally worse as leaching of low level template impurities prevented detection of the target analyte at low concentrations (5 ngmL(-1)). This relatively poorer performance was evident as worse accuracy at low concentrations with a consequent higher limit of quantification than the conventional methods.

Digital photography: a new method for estimating food intake in cafeteria settings

OBJECTIVE

The primary objective of this study was to test the comparability of digital photography and visual estimation procedures for estimating food intake.

RESEARCH METHODS AND PROCEDURES

The study sample included 71 breakfast meals and 59 lunch meals eaten in a university cafeteria during a single day. A total of 66 different foods were employed as test foods that could be selected by the students. Food selections and plate waste, as estimated by digital photography and visual estimation, were compared. For digital photography, three observers independently estimated portion sizes of each food item based upon digital photographs. One observer estimated portion sizes in the cafeteria setting, using visual estimation, a method that has been validated in other studies.

RESULTS

To test the accuracy of the two procedures for measuring food intake, the estimates of food weights derived from both procedures were compared using Bland-Altman regression. In comparison to visual estimation, the digital photography method yielded comparable estimates of food selections, plate waste, and total food intake for seven of nine comparisons. The two methods of estimating food portions yielded comparable results for most (78%) types of foods. The two methods also yielded similar variability.

DISCUSSION

These findings suggest that the digital photography method is an alternative to the traditional method of estimating food intake via direct observation.

Isolation of a rhabdovirus during outbreaks of disease in cyprinid fish species at fishery sites in England

A virus was isolated during disease outbreaks in bream Abramis brama, tench Tinca tinca, roach Rutilis rutilis and crucian carp Carassius carassius populations at 6 fishery sites in England in 1999. Mortalities at the sites were primarily among recently introduced fish and the predominant fish species affected was bream. The bream stocked at 5 of the 6 English fishery sites were found to have originated from the River Bann, Northern Ireland. Most fish presented few consistent external signs of disease but some exhibited clinical signs similar to those of spring viraemia of carp (SVC), with extensive skin haemorrhages, ulceration on the flanks and internal signs including ascites and petechial haemorrhages. The most prominent histopathological changes were hepatocellular necrosis, interstitial nephritis and splenitis. The virus induced a cytopathic effect in tissue cultures (Epithelioma papulosum cyprini [EPC] cells) at 20 degrees C and produced moderate signals in an enzyme immunoassay (EIA) for the detection of SVC virus. The virus showed a close serological relationship to pike fry rhabdovirus in both EIA and serum neutralisation assays and to a rhabdovirus isolated during a disease outbreak in a bream population in the River Bann in 1998. A high degree of sequence similarity (> or = 99.5% nucleotide identity) was observed between the English isolates and those from the River Bann. Experimental infection of juvenile bream, tench and carp with EPC cell-grown rhabdovirus by bath and intraperitoneal injection resulted in a 40% mortality of bream in the injection group only. The virus was re-isolated from pooled kidney, liver and spleen tissue samples from moribund bream. The field observations together with the experimental results indicate that this rhabdovirus is of low virulence but may have the potential to cause significant mortality in fishes under stress.

The effect of erythromycin on the pharmacokinetics of rosuvastatin

RATIONALE OBJECTIVE

To examine in vivo the effect of erythromycin on the pharmacokinetics of rosuvastatin [an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase]. Erythromycin is a potent inhibitor of CYP3A4 that markedly increases circulating levels of some other HMG-CoA reductase inhibitors.

METHODS

In this randomised, double-blind, two-way cross-over, placebo-controlled trial 14 healthy volunteers were given 500 mg erythromycin or placebo four times daily for 7 days. A single dose of 80 mg rosuvastatin was co-administered on day 4 of dosing. Plasma concentrations of rosuvastatin and active and total HMG-CoA reductase inhibitors were measured up to 96 h after dosing.

RESULTS

Eleven volunteers had data available from both dosing periods. There was no increase in rosuvastatin plasma exposure following co-administration with erythromycin compared to placebo. In fact, following co-administration with erythromycin, rosuvastatin geometric least square mean AUC((0-t)) and C(max) were 20% and 31%, respectively, lower than with placebo. Individual treatment ratios for AUC((0-t)) ranged from 0.48 to 1.17, and for C(max) ranged from 0.33 to 2.19. Essentially all of the circulating active HMG-CoA reductase inhibitors and most (>94%) of the total inhibitors were accounted for by rosuvastatin. Erythromycin did not affect the proportion of circulating active or total inhibitors accounted for by circulating rosuvastatin.

CONCLUSIONS

Erythromycin did not produce any increase in rosuvastatin plasma exposure. This indicates that CYP3A4 metabolism is not an important clearance mechanism for rosuvastatin, a result consistent with previous findings. The small decreases in rosuvastatin AUC((0-t)) and C(max) that occurred as a consequence of short-term treatment with erythromycin are unlikely to have relevance to long-term treatment with rosuvastatin.

Pharmacokinetics and pharmacodynamics of rosuvastatin in subjects with hepatic impairment

OBJECTIVE

To assess the effect of chronic hepatic impairment on rosuvastatin disposition, pharmacodynamic activity and tolerability.

METHODS

This was an open-label, non-randomised, parallel-group trial. Six subjects were enrolled in each of three hepatic-function strata: Child-Pugh class A (CP-A, mild impairment), Child-Pugh class B (CP-B, moderate impairment) and normal hepatic function; the latter two strata were age, weight, race, sex and smoking history matched. All subjects were given rosuvastatin 10 mg for 14 days.

RESULTS

In subjects with CP-A, and in four of six subjects with CP-B, rosuvastatin steady-state AUC(0-24) and C(max) were similar to subjects with normal hepatic function (geometric mean values 60.7 ng h/ml and 6.02 ng/ml, respectively). Two of six subjects with CP-B who had the highest CP scores (i.e. the highest degrees of hepatic impairment) had the highest AUC(0-24) (128 ng h/ml and 242 ng h/ml) and C(max) (23.4 ng/ml and 96.7 ng/ml) values. Low-density lipoprotein cholesterol (LDL-C) was decreased in all strata, but the response was more variable in the CP-B group. Rosuvastatin was well tolerated, and the safety profile was similar in subjects with hepatic impairment and normal hepatic function.

CONCLUSION

In most subjects with mild-to-moderate hepatic impairment, the steady-state pharmacokinetics of rosuvastatin were similar to subjects with normal hepatic function (more extensive hepatic impairment may increase systemic exposure to rosuvastatin), and most had LDL-C reductions similar to subjects with normal hepatic function.

The effect of fluconazole on the pharmacokinetics of rosuvastatin

OBJECTIVE

To examine the effect of fluconazole, a potent inhibitor of CYP2C9 and CYP2C19, on the pharmacokinetics of rosuvastatin in healthy volunteers. Significantly increased plasma concentrations of fluvastatin have been observed following co-administration with fluconazole.

METHODS

This was a randomised, double-blind, two-way crossover, placebo-controlled trial. Healthy male volunteers ( n=14) were given fluconazole 200 mg or matching placebo once daily for 11 days; rosuvastatin 80 mg was co-administered on day 8 of dosing. Plasma concentrations of rosuvastatin, N-desmethyl rosuvastatin, and active and total 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors were measured up to 96 h post-dose.

RESULTS

Following co-administration with fluconazole, rosuvastatin geometric least-square mean area under the plasma concentration-time curve (AUC(0-t)) and peak plasma concentration (C(max)) were increased by 14% and 9%, respectively, compared with placebo (90% confidence intervals for the treatment ratios: 0.967 to 1.341 and 0.874 to 1.355, respectively). Individual treatment ratios for AUC(0-t) ranged from 0.59 to 2.23, and for C(max) ranged from 0.52 to 2.28. The limited data available for the N-desmethyl metabolite show that geometric mean C(max) was decreased by approximately 25% compared with placebo. Rosuvastatin accounted for essentially all of the circulating active HMG-CoA reductase inhibitors and most (>90%) of the total inhibitors. Fluconazole did not affect the proportion of circulating active or total inhibitors accounted for by circulating rosuvastatin.

CONCLUSIONS

Fluconazole produced only small increases in rosuvastatin AUC(0-t) and C(max), which were not considered to be of clinical relevance. The results support previous in-vitro findings that CYP2C9 and CYP2C19 metabolism is not an important clearance mechanism for rosuvastatin.

Adolescent premarital sexual activity, cohabitation, and attitudes toward marriage

Societal trends indicate ambivalent attitudes about marriage. Specifically, there is greater acceptance of divorce and nontraditional living arrangements such as cohabitation, as well as acceptance and prevalence of premarital sex, than in the past. The authors examine adolescent attitudes toward marriage and their association with premarital sexual activity and cohabitation. Recommendations for helping adolescents understand the realities of marriage and family life are shared.

Quantification of rosuvastatin in human plasma by automated solid-phase extraction using tandem mass spectrometric detection

An assay employing automated solid-phase extraction (SPE) followed by high-performance liquid chromatography with positive ion TurboIonspray tandem mass spectrometry (LC-MS-MS) was developed and validated for the quantification of rosuvastatin (Crestor) in human plasma. Rosuvastatin is a hydroxy-methyl glutaryl coenzyme A reductase inhibitor currently under development by AstraZeneca. The standard curve range in human plasma was 0.1-30 ng/ml with a lower limit of quantification (LLOQ) verified at 0.1 ng/ml. Inaccuracy was less than 8% and imprecision less than +/-15% at all concentration levels. There was no interference from endogenous substances. The analyte was stable in human plasma following three freeze/thaw cycles and for up to 6 months following storage at both -20 and -70 degrees C. The assay was successfully applied to the analysis of rosuvastatin in human plasma samples derived from clinical trials, allowing the pharmacokinetics of the compound to be determined.

Locomotion towards a goal alters the synchronous firing of neurons recorded simultaneously in the subiculum and nucleus accumbens of rats

Rats were implanted with recording electrodes aimed at the subiculum and nucleus accumbens. They were subsequently placed in a cylindrical environment, where they searched for locations where they would receive rewarding medial forebrain bundle stimulation. At times a tone was sounded, indicating that the reward location was in the center of the environment. Animals quickly learned to switch from random running to goal directed locomotion when the tone was on. To quantify the synchronous firing between simultaneously recorded neurons in the subiculum and nucleus accumbens, a gravitational clustering algorithm was employed. Individual neurons were modeled as particles in N dimensional space. Every spike discharge of the neuron augmented the 'gravitational charge' on its model particle. Synchronous firing between two cells caused their corresponding particles to draw together over time, due to the concurrent appearance of gravitational charge. All pair-wise combinations of cells isolated in subiculum and nucleus accumbens were examined using this algorithm. The firing of nine out of 52 subicular-accumbens cell pairings was significantly more synchronous when the tone was on, and the rat was running towards the central goal. This was also seen for 15 out of 22 subicular-subicular cell pairings. Conversely, only two out of 51 accumbens-accumbens pairings displayed significant tone dependent changes in synchronous firing. Thus, synchronous interactions between subiculum and nucleus accumbens occur preferentially when the animal is required to locate a fixed goal in space, i.e., the functional connectivity is altered by the navigational demands of the spatial reward task.

Determination of mevalonic acid in human urine as mevalonic acid lactone by gas chromatography-mass spectrometry

Mevalonic acid in urine is converted to its lactone form by incubation overnight at acidic pH, extracted and analysed by GC-MS. The lower limit of quantitation of 7.5 ng/ml provides adequate sensitivity to measure changes in urinary excretion of MVA following administration of drugs which affect cholesterol synthesis. The assay is linear up to 300 ng/ml and has acceptable precision (<15%) and accuracy (<+/-20%) across the calibration range.

An unexpected selectivity of a propranolol-derived molecular imprint for tamoxifen

During the evaluation of molecular imprinted polymers (MIPs) prepared against the drug tamoxifen a propranolol-derived MIP was used as a positive control. Surprisingly the propranolol-derived MIP showed considerable selectivity towards tamoxifen, and was indeed much more selective than the MIP prepared using tamoxifen as the imprint molecule. The consequences of this unexpected, cross reactivity for the use of MIPs in analytical chemistry is discussed.

Criminal DNA databases: the European situation

In the last 5 years, a number of European countries have successfully introduced national databases holding the DNA profiles from suspected and convicted criminal offenders as well as from biological stain materials from unsolved crime cases. At present, DNA databases are fully or partially in operation in the UK, The Netherlands, Austria, Germany, Finland, Norway, Denmark, Switzerland and Sweden. Furthermore, in the other European countries, specific legislation will be enacted soon, or the introduction of such databases is being discussed to initiate a legislative process. Numerous differences exist regarding the criteria for a criminal offender to be included in the database, the storage periods and the possibility to remove database records, the possibility to keep reference samples from the offenders as long as their respective records are being held, and the role of judges in the process of entering a database record or to perform a database search. Nevertheless, harmonization has been achieved regarding the DNA information stored in national databases, and a European standard set of genetic systems has been recommended which is included either in part or completely in the DNA profiles of offenders and crime stains for all European databases. This facilitates the exchange of information from database records to allow the investigation of crime cases across national borders.

A brief history of the formation of DNA databases in forensic science within Europe

The introduction of DNA analysis to forensic science brought with it a number of choices for analysis, not all of which were compatible. As laboratories throughout Europe were eager to use the new technology different systems became routine in different laboratories and consequently, there was no basis for the exchange of results. A period of co-operation then started in which a nucleus of forensic scientists agreed on an uniform system. This collaboration spread to incorporate most of the established forensic science laboratories in Europe and continued through two major changes in the technology. At each step agreement was reached on which systems to use. From the beginning it was realised that DNA databases would provide the criminal justice systems with an efficient way of crime solving and consequently some local databases were created. It was not until the introduction of the amplification technology linked to the analysis of short tandem repeats that a sufficiently sensitive and robust system was available for the formation of efficient and effective DNA databases. Comprehensive legislation enacted in the UK in 1995 enabled forensic scientists to set up the first national DNA database which would hold both personal DNA profiles together with results obtained from crime scenes. Other countries quickly followed but in some the legislation has severely restricted the amount and type of data which can be retained and, therefore, effectiveness of the databases is limited. The widespread use of commercially produced multiplex kits has produced a situation in which nearly all European laboratories are using compatible systems and there is, therefore, the potential for the introduction of a pan-European DNA database. However, the exchange of results between countries is hampered by the various legislations which currently exist.

Disparate effects of long-term potentiation on evoked potentials and single CA1 neurons in the hippocampus of anesthetized rats

To examine the effects of long-term potentiation (LTP) on individual neurons in the intact brain, anesthetized rats were implanted with a recording stereotrode in the right CA1 layer of the hippocampus and a stimulating electrode in the right and left CA3 layers. The evoked and spontaneous firing of single CA1 neurons was characterized before and after LTP of the contralateral (commissural) Schaffer collaterals and again after LTP of the ipsilateral (associational) Schaffer collaterals. Individual CA1 neurons displayed either increases or decreases in evoked and spontaneous firing after LTP. As many as five discriminated cells were recorded simultaneously, and they typically responded discordantly, so that after LTP, firing in some neurons increased while in others it decreased. The response of individual neurons to in vivo LTP may be modulated by heterogeneous synaptic changes on individual and local groups of cells, and by changes in feed-forward excitation and inhibition provided by local hippocampal circuitry.

Knowledge and attitudes of family physicians about clinical practice guidelines and the care of patients with type 2 diabetes mellitus

This study examined the attitudes of Louisiana family physicians toward clinical practice guidelines in general and specifically how attitudes and familiarity with the American Diabetes Association Clinical Recommendations (ADACR) correlated with knowledge and evidence-based "best practice" in the care of type 2 diabetes. Surveys were mailed to a random sample of 278 eligible physicians from which a 32% response rate was obtained (n = 90). Family physicians' general attitudes towards guidelines were neutral. Attitude correlated significantly with knowledge of the ADACR (P = .03) but not with "best practice". Despite low scores for knowledge, all but one of the ADACR were adhered to by more than 85% of respondents. Physician attitudes do not appear to be barriers to guideline implementation. Results may be used to focus studies of processes and outcomes in guideline implementation.

Effects of reward anticipation, reward presentation, and spatial parameters on the firing of single neurons recorded in the subiculum and nucleus accumbens of freely moving rats

The subiculum is the major output of the hippocampal formation (involved in spatial processing). Subicular afferents innervate the nucleus accumbens, which is thought to integrate limbic reward information with motor output. Rats were chronically implanted with extra-cellular recording electrodes aimed at both structures to investigate the functional relationship between them. Animals were then trained on a spatial task in which they searched for random locations where they would receive rewarding medial forebrain bundle stimulation. At random times a cue tone was sounded, indicating that the reward location was in the center of the environment. Rats quickly learned to run to the center upon hearing the tone in order to receive a reward. Simultaneously recorded groups of up to eight subicular and accumbens neurons were found to display alterations in firing rate after rewarding medial forebrain bundle stimulation. Moreover, neurons in both subiculum and accumbens displayed alterations in firing rate prior to arrival at the center during cued runs, i.e. they anticipated predictable rewards. Subicular and accumbens firing was also correlated with spatial location. However, neurons in accumbens were more likely to respond to task events, and these responses were more varied, than those seen in subiculum. Thus, while convergence of spatial and reward information occurs at the level of single cells in both subiculum and nucleus accumbens, these structures also display functional localization.

A combined electrophysiological and video data acquisition system using a single computer

Numerous experimental paradigms in behavioral electrophysiology and neuroethology require simultaneous recording of neural signals and behavior. A computer fitted with an analog to digital converter and a frame grabber was configured to perform both tasks. The analog to digital converter collected electrophysiological data while the frame grabber recorded video images. Since spike and image information were present in one computer, arbitrary combinations of electrophysiological and behavioral parameters could be used as the basis of an operant conditioning paradigm. The system was used to record subicular cell firing in rats performing a place search task. The computer monitored the output of the analog to digital converter for supra-threshold events. When one was detected, a block of samples (pre- and post-trigger) was stored in memory. The same computer also scanned every video frame to find the rat, and recorded a image of its behavior. The location of the rat was then quickly calculated. If it satisfied the task conditions, a brain reward pathway (medial forebrain bundle) was stimulated. The recording of neural and image data was monitored in real-time by writing spike waveforms and location data directly to video card RAM.

Severe alpha1-antitrypsin deficiency and pregnancy

This case study describes a successful pregnancy in a 27-yr-old patient with severe emphysema, secondary to alpha1-antitrypsin deficiency, genotype PiZZ. Despite significant respiratory compromise, more severe than previously reported, no complications ensued. Maternal pulmonary function did not deteriorate significantly until the 32nd week of pregnancy, with an elective Caesarean section being performed during the 37th week. This experience suggests that even severe maternal airflow obstruction is, in itself, not an absolute contra-indication to pregnancy. Pre-pregnancy multidisciplinary counselling is likely to be helpful in these patients, including frank discussion on the risks of pregnancy, the prospects of successful completion and the mother's future prognosis in relation to caring for the child.

Nurse practitioners and the problem of discounting

Nurse practitioners (NPs) are key primary care providers in health care reform. The purpose of this paper is to discuss discounting, a social problem for NPs discovered in this grounded theory study. Discounting refers to behaviours directed towards NPs that they perceived as degrading. Data collection included open-ended, in-depth interviews on the nature of NP practice with 23 NPs, and 10 key members representing the Florida State Board of Nursing, Florida Nurses Association, American Nurses Association, and National Council of State Boards of Nursing. Excerpts that illuminated discounting were obtained from field notes about organizational documents, state legislative committee hearings, and professional NP association meetings. Data analysis using the grounded theory method revealed that NPs in this study struggled to establish their roles from a position of marginality in a context of conflict and negativity. NPs were subjected to social psychological and social structural discounting. This research serves to raise the consciousness of NPs with the hope that such awareness will facilitate personal and group action to combat discounting in their daily work and at local, state and national levels.

Salts on Europa's surface detected by Galileo's near infrared mapping spectrometer. The NIMS Team

Reflectance spectra in the 1- to 2.5-micrometer wavelength region of the surface of Europa obtained by Galileo's Near Infrared Mapping Spectrometer exhibit distorted water absorption bands that indicate the presence of hydrated minerals. The laboratory spectra of hydrated salt minerals such as magnesium sulfates and sodium carbonates and mixtures of these minerals provide a close match to the Europa spectra. The distorted bands are only observed in the optically darker areas of Europa, including the lineaments, and may represent evaporite deposits formed by water, rich in dissolved salts, reaching the surface from a water-rich layer underlying an ice crust.

Place field dynamics and directionality in a spatial memory task

In previous studies place fields have been shown to be governed by one or more polarizing stimuli such that rotation of the stimuli caused concomitant rotation of the fields. Place fields have also been observed to persist after removal of stimulus cues. In the present study we confirm the previous findings and report two new responses. Hippocampal place fields were observed to decrease or cease place specific firing after the removal of the polarizing cues. Others increased or initiated place specific firing after cue removal. Thus in these instances place field location was dependent on the orientation of the polarizing cues but place field magnitude was governed by their presence or absence. A subset of the place fields recorded in the present study were found to display directionality. Place field directionality was found to be governed by the polarizing cues such that cue rotation produced concomitant rotation in the direction of maximal firing. However directionally specific firing was unaffected by cue removal. These results suggest that place field directionality is initially set up by the polarizing cues but is subsequently independent of them.

New insights into the regulation of the blood clotting cascade derived from the X-ray crystal structure of bovine meizothrombin des F1 in complex with PPACK

BACKGROUND

The conversion of prothrombin to thrombin by factor Xa is the penultimate step in the blood clotting cascade. In vivo, where the conversion occurs primarily on activated platelets in association with factor Va and Ca2+ ions, meizothrombin is the major intermediate of the two step reaction. Meizothrombin rapidly loses the fragment 1 domain (F1) by autolysis to become meizothrombin des F1 (mzTBN-F1). The physiological properties of mzTBN-F1 differ dramatically from those of thrombin due to the presence of prothrombin fragment 2 (F2), which remains covalently attached to the activated thrombin domain in mzTBN-F1.

RESULTS

The crystal structure of mzTBN-F1 has been determined at 3.1 A resolution by molecular replacement, using only the thrombin domain, and refined to R and Rfree values of 0.205 and 0.242, respectively. The protease active site was inhibited with D-Phe-Pro-Arg-chloromethylketone (PPACK) to reduce autolysis. The mobile linker chain connecting the so-called kringle and thrombin domains and the first two N-acetylglucosamine residues attached to the latter were seen in electron-density maps improved with the program SQUASH. Previously these regions had only been modeled.

CONCLUSIONS

The F2 kringle domain in mzTBN-F1 is bound to the electropositive heparin-binding site on thrombin in an orientation that is systematically shifted and has significantly more interdomain contacts compared to a noncovalent complex of free F2 and free thrombin. F2 in mzTBN-F1 forms novel hydrogen bonds to the carbohydrate chain of thrombin and perhaps stabilizes a unique, rigid conformation of the gamma-autolysis loop through non-local effects. The F2 linker chain, which does not interfere with the active site or fibrinogen-recognition site, is arranged so that the two sites cleaved by factor Xa are separated by 36 A. The two mzTBN-F1 molecules in the asymmetric unit share a tight 'dimer' contact in which the active site of one molecule is partially blocked by the F2 kringle domain of its partner. This interaction suggests a new model for prothrombin organization.

Organics and other molecules in the surfaces of Callisto and Ganymede

Five absorption features are reported at wavelengths of 3.4, 3.88, 4. 05, 4.25, and 4.57 micrometers in the surface materials of the Galilean satellites Callisto and Ganymede from analysis of reflectance spectra returned by the Galileo mission near-infrared mapping spectrometer. Candidate materials include CO2, organic materials (such as tholins containing C(triple bond)N and C-H), SO2, and compounds containing an SH-functional group; CO2, SO2, and perhaps cyanogen [(CN)2] may be present within the surface material itself as collections of a few molecules each. The spectra indicate that the primary surface constituents are water ice and hydrated minerals.

Crystal structure of fibrinogen-Aalpha peptide 1-23 (F8Y) bound to bovine thrombin explains why the mutation of Phe-8 to tyrosine strongly inhibits normal cleavage at Arg-16

A peptide containing residues 1-50 of the Aalpha-chain of fibrinogen, expressed as a fusion peptide with beta-galactosidase, is rapidly cleaved by thrombin at Arg-16, similarly to whole fibrinogen. When Phe-8, which is highly conserved, is replaced with tyrosine (F8Y), the cleavage is slowed drastically [Lord, Byrd, Hede, Wei and Colby (1990) J. Biol. Chem. 265, 838-843]. To examine the structural basis for this result, we have determined the crystal structure of bovine thrombin complexed with a synthetic peptide containing residues 1-23 of fibrinogen Aalpha and the F8Y mutation. The crystals are in space group P43212, with unit-cell dimensions of a = 88.3 A (1 A = 0.1 nm), c = 195.5 A and two complexes in the asymmetric unit. The final R factor is 0.183 for 2sigma data from 7.0 to 2.5 A resolution. There is continuous density for the five residues in the P3, P2, P1, P1' and P2' positions of the peptide (Gly-14f to Pro-18f) at the active site of thrombin, and isolated but well-defined density for Tyr-8f at position P9 in the hydrophobic pocket of thrombin. The tyrosine residue is shifted relative to phenylalanine in the native peptide because the phenol side chain is larger and makes a novel, intrapeptide hydrogen bond with Gly-14f. Adjacent peptide residues cannot form the hydrogen bonds that stabilize the secondary structure of the native peptide. Consequently, the 'reaction'geometry at the scissile bond, eight residues from the mutation, is perturbed and the peptide is mostly uncleaved in the crystal structure.

The co-crystal structure of unliganded bovine alpha-thrombin and prethrombin-2: movement of the Tyr-Pro-Pro-Trp segment and active site residues upon ligand binding

Unliganded bovine alpha-thrombin and prethrombin-2 have been co-crystallized, in space group P21212, using either ammonium sulfate or polyethylene glycol 2000 (PEG2K), and their structures determined at 2.2 A and 2.3 A, respectively. Initial phases were determined by molecular replacement and refined using XPLOR to final R factors of 0.187 (Rfree = 0.255) and 0.190 (Rfree = 0.282) for the salt and PEG2K models, respectively. The apo-enzyme form of bovine alpha-thrombin shows dramatic shifts in placement for the Tyr-Pro-Pro-Trp segment, for Glu-192, and for the catalytic residues His-57 and Ser-195, when compared to 4 thrombin complexes representing different states of catalysis, namely (1) the Michaelis complex (residues 7-19 of fibrinogen A alpha with a non-cleavable scissile bond), (2) enzyme-inhibitor complex (D-Phe-Pro-Arg chloromethylketone), (3) enzyme product complex (residues 7-16 of fibrinopeptide A), and (4) the exosite complex (residues 53-64 of hirudin). The structures of bovine and human prethrombin-2 are generally similar to one another (RMS deviation of 0.68 A) but differ significantly in the Arg-15/Ile-16 cleavage region and in the three activation domains, which are disordered in bovine prethrombin-2, analogous to that seen for trypsinogen.

Crystal structure of a class I ubiquitin conjugating enzyme (Ubc7) from Saccharomyces cerevisiae at 2.9 angstroms resolution

Ubiquitin-conjugating enzymes are a family of related proteins that participate in the ubiquitination of proteins. Previous studies on the crystal structures of Saccharomyces cerevisiae Ubc4 and Arabidopsis thaliana Ubc1 indicated that the smallest enzymes (class I), which consist entirely of the conserved core domain, share a common tertiary fold. Here we report the three-dimensional structure of the S. cerevisiae class I enzyme encoded by the UBC7 gene. The crystal structure has been solved using molecular replacement techniques and refined by simulated annealing to an R-factor of 0.183 at 2.93 A resolution. Bond lengths and angles in the molecule have root-mean-square deviations from ideal values of 0.016 A and 2.3 degrees, respectively. Ubc7 is an alpha/beta protein with four alpha-helices and a four-stranded antiparallel beta-sheet. With the exception of two regions where extra residues are present, the tertiary folding of Ubc7 is similar to those of the other two enzymes. The ubiquitin-accepting cysteine is located in a cleft between two loops. One of these loops is nonconserved, as this region of the Ubc7 molecule differs from the other two enzymes by having 13 extra residues. There is also a second single amino acid insertion that alters the orientation of the turn between the first two beta-strands. Analysis of the 13 ubiquitin-conjugating enzyme sequences in S. cerevisiae indicates that there may be two other regions where extra residues could be inserted into the common tertiary fold. Both of these other regions exhibit significant deviations in the superposition of the three structures and, like the two insertion regions in Ubc7, may represent hypervariable regions within a common tertiary fold. As ubiquitin-conjugating enzymes interact with different substrates or other accessory proteins in the ubiquitination pathway, these variable surface regions may confer distinct specificity to individual enzymes.

Negotiating symbolic space: strategies to increase NP status and value

Nurse practitioners (NPs) have an unprecedented opportunity to become key primary health care providers, yet barriers to independent practice still exist. The purpose of this research was to explore and describe the practice of NPs from their perspective. Open-ended, interactive interviews were conducted with 23 NPs. Data analysis using the grounded theory method revealed that NPs attempt to establish their roles from a marginalized position and are often subjected to psychological and structural discounting. To combat discounting, the NPs in this research worked to negotiate the symbolic space required for their acceptance as valued health care providers. They used techniques of cultivating, bargaining, confronting, and disengaging. All of these techniques promote NP role definition by generating and preserving role boundaries, thereby moving NPs toward the symbolic space necessary for them to become part of the national consciousness. This research contributes to clarification of the NP role and the building of a formal theory of advanced nursing practice.

Anaesthetic management of a child undergoing thoracoscopic removal of a lung cyst

The anaesthetic management of a child undergoing video-assisted thoracoscopic resection of a large lung cyst is described. In particular, we discuss the prolonged postoperative stay, which resulted from persistent pneumothorax, and his need for substantial analgesia up to the twelfth postoperative day-which seemed no shorter than might have been expected following a thoracotomy. While other workers have claimed advantages with thoracoscopic operations, in terms of reduced pain and morbidity, compared to traditional thoracotomy, we feel that one should be aware of the potential for severe postoperative pain in these patients.

Bovine thrombin complexed with an uncleavable analog of residues 7-19 of fibrinogen A alpha: geometry of the catalytic triad and interactions of the P1', P2', and P3' substrate residues

The crystal structure of the noncovalent complex of bovine thrombin and a fibrinogen-A alpha tridecapeptide substrate analog, G17 psi, in which the scissile bond amide nitrogen of Gly-17f has been replaced by a methylene carbon, has been determined at 2.3 A resolution with an R factor of 17.1%. The geometry of the active site indicates that the crystal structure is a close model of the true Michaelis complex. The three independently determined thrombin/G17 psi complexes in the crystal asymmetric unit reveal novel interactions for the P2' and P3' residues-Pro-18f and Arg-19f, respectively-on the carboxyl-terminal side of the scissile bond and confirm previously observed interactions of the P1 (Arg-16f) through P10 (Asp-7f) positions on the amino-terminal side. The thrombin S2' binding site for Pro-18f, as observed in all three complexes, differs from that predicted by modeling studies and is notable for including two carbonyl oxygens of the thrombin main chain. Arg-19f occupies two binding sites on thrombin, S3'A and S3'B, which have dramatically different placements for the arginyl side chain and carboxyl terminus.

The role of the dodecamer subunit in the dissociation and reassembly of the hexagonal bilayer structure of Lumbricus terrestris hemoglobin

The dissociation of the approximately 3500-kDa hexagonal bilayer (HBL) hemoglobin (Hb) of Lumbricus terrestris upon exposure to Gdm salts, urea and the heteropolytungstates [SiW11O39]8- (SiW), [NaSb9W21O86]18- (SbW) and [BaAs4W40O140]27- (AsW) at neutral pH was followed by gel filtration, SDS-polyacrylamide gel electrophoresis, and scanning transmission electron microscopy. Elution curves were fitted to sums of exponentially modified gaussians to represent the peaks due to undissociated oxyHb, D (approximately 200 kDa), T+L (approximately 50 kDa), and M (approximately 25 kDa) (T = disulfide-bonded trimer of chains a c, M = chain d, and L = linker chains). OxyHb dissociation decreased in the order Gdm*SCN > Gdm.Cl > urea > Gdm.OAc and AsW > SbW > SiW. Scanning transmission electron microscopy mass mapping of D showed approximately 10-nm particles with masses of approximately 200 kDa, suggesting them to be dodecamers (a+b+c)3d3. OxyHb dissociations in urea and Gdm.Cl and at alkaline pH could be fitted only as sums of 3 exponentials. The time course of D was bell-shaped, indicating it was an intermediate. Dissociations in SiW and upon conversion to metHb showed only two phases. The kinetic heterogeneity may be due to oxyHb structural heterogeneity. Formation of D was spontaneous during HBL reassembly, which was minimal (</= 10%) without Group IIA cations. During reassembly, maximal (approximately 60%) at 10 mM cation, D occurs at constant levels (approximately 15%), implying the dodecamer to be an intermediate.

Mass spectrometric composition and molecular mass of Lumbricus terrestris hemoglobin: a refined model of its quaternary structure

Sedimentation equilibrium measurements and scanning transmission electron microscopy (STEM) mass mapping of the extracellular, hexagonal bilayer hemoglobin (HBL Hb) of the earthworm Lumbricus terrestris provided masses of 3.41 to 3.66 MDa and 3.56 (+/- 0.13) MDa, respectively. The Hb also contains 57.2 (+/- 6.0) moles of tightly bound Ca per mole of protein. The Hb and its subunits obtained by dissociation, in native, dehemed and reduced carbamidomethylated forms, were subjected to electrospray ionization mass spectroscopy (ESI-MS). Maximum entropy deconvolution identified three groups of peaks, at approximately 16 kDa, 24 to 32 kDa and approximately 53 kDa corresponding to the monomer subunit M (globin chain d), four linker subunits and the disulfide-bonded trimer T (globin chains a + b + c). Subunit M consisted of three components, d1 (15, 992.4), d2 (15, 978.0) and d3 (15, 962.1) (+/- 1.0 Da), with relative intensities 1.0:5:0.3, respectively. Subunit T consisted of four major components, T1 (52, 922.6), T2 (52, 760.0), T3 (52, 598.5) and T4 (52, 435.4) (+/- 4.0 Da), with relative intensities 0.6:1.0:0.2:0.7, respectively. ESI-MS of carbamidomethylated T, demonstrated that, unlike chains b (16, 254.4) and c (17, 289.2), chain a exists as a series of four, hexose-connected, glycosylated isoforms, a1 to a4 (19, 389.9, 19, 227.4, 19, 065.3 and 18, 902.9) (+/- 1.0 Da). The mass differences between the deglycosylated chain a (17, 524.0) and a1 to a4 correspond to glycan side-chains (GlcNAc)2 (Man)n (n = 6 to 9). Four groups of peaks were observed in the 24 to 32 kDa region. Linkers L1a (27, 540.8) and L1b (27, 702.4) (+/- 2.0 Da) are isoforms of L1 (25, 837.5 in N-deglycosylated Hb) with glycan side-chains (GlcNAc)2 (Man)n (n = 8,9). Linkers L2 (32, 104.3 (+/- 5.0) Da) and L3 (24, 912.9 (+/- 2.0) Da) occur as single species. Linkers L4a to L4c (24, 019.0, 24, 102.3 and 24, 169.9) (+/- 2.0 Da) with relative intensities 1.0:0.8:0.8, have not been identified previously. From ESI-MS relative intensities, L1:L2:L3:L4 = 0.6:0.4:1.0:0.5 and globin linker = 0.78:0.22. HPLC of Lumbricus Hb provided a globin linker = 0.73:0.27 (+/- 0.02) and a heme content of 2.52 (+/- 0.14) wt%. A model is proposed for the HBL structure, wherein 12 213.4 kDa dodecamers (144 globin chains, 2561 kDa) decorate a hexagonal framework of 36 linker chains (12L1 + 6L2 + 12L3 + 6L4) to provide a total mass of 3.531 MDa, each dodecamer being in contact with three linker subunits.

Molecular symmetry of the dodecamer subunit of Lumbricus terrestris hemoglobin

The principal functional subunit of the approximately 3500 kDa extracellular Lumbricus terrestris hemoglobin is a 213 kDa dodecamer of four chemically distinct globin chains, consisting of a non-covalent complex of three trimer submits (disulfide-bonded chains a, b and c) and three monomer subunits (chain d). X-ray diffraction of crystals of the dodecamer grown at neutral pH, were found to be monoclinic, with the unit cell dimensions: a = 112.3 A, b = 190.0 A, c = 69.6 A, beta = 102.0 degrees with h + k + l = 2n + 1 absent, characteristic of space group I121. In addition, these crystals exhibit a pseudo trigonal P321 symmetry with unit cell dimensions a = 190.5 A, b = 190.5 A, c = 69.5 A, gamma = 120.0 degrees. Assuming that the assymetric unit contains an entire dodecamer, a model of the latter was constructed that satisfies the symmetry of the trigonal pseudo cell and is consistent with the symmetry of the I121 crystallographic cell. The resulting model has strong implications concerning the hexagonal bilayer structure of the native hemoglobin.

1.6 Å structure of semisynthetic ribonuclease crystallized from aqueous ethanol. Comparison with crystals from salt solutions and with ribonuclease A from aqueous alcohol solutions

The non-covalent combination of residues 1-118 of RNase A with a synthetic 14-residue peptide containing residues 111-124 of the molecule forms a highly active semisynthetic enzyme, RNase 1-118:111-124. With this enzyme, the roles played by the six C-terminal residues in generating the catalytic efficiency and substrate specificity of RNase can be studied using chemically synthesized analogs. The structure of RNase 1-118:111-124 from 43% aqueous ethanol has been determined using molecular-replacement methods and refined to a crystallographic R-factor of 0.166 for all observed reflections in the range 7.0-1.6 A (Protein Data Bank file ISSC). The structure is compared with the 2.0 A structure of RNase A from 43% aqueous 2-methyl-2-propanol and with the 1.8 A structure of the semisynthetic enzyme obtained from crystals grown in concentrated salt solution. The structure of RNase 1-118:111-124 from aqueous ethanol is virtually identical to that of RNase A from aqueous 2-methyl-2-propanol. Half of the crystallographically bound water molecules are not coincident, however. The structure is somewhat less similar to that of RNase 1-118:111-124 from salt solutions, with a major difference being the positioning of active-site residue His119.

The safety, tolerability and efficacy of transdermal nicotine (Nicotinell TTS) in initially hospitalised patients

AIM

We studied a transdermal nicotine system with minimal behavioural intervention in hospitalised patients to assess patient acceptability, safety and efficacy.

METHOD

In an open noncomparative study, 80 smoking patients (42 men and 38 women) were enrolled. They received 24-hour nicotine patches and simple support for 12 weeks and were followed for up to 26 weeks. Smoking was assessed by interview, expired air carbon monoxide and blood cotinine.

RESULTS

Side effects included itch and local erythema (4), insomnia (7), abnormal taste (3). Two subjects withdrew from the study because of side effects. At 12 weeks 17 were nonsmokers. At 26 weeks 19 of 80 were nonsmokers and a further 14 had reduced their intake significantly.

CONCLUSIONS

The nicotine skin patch proved to be safe and well tolerated. Efficacy was comparable to controlled trials of transdermal nicotine patches.

Preliminary X-ray diffraction analysis of crystals of the PII protein from Escherichia coli

PII protein, which carries metabolic signals regulating the transcription and activity of glutamine synthetase in nitrogen assimilation in Escherichia coli, has been crystallized in space group P2(1) with a = 47.8 A, b = 62.9 A, c = 52.8 A and beta = 100.3 degrees and space group P2(1)2(1)2(1) with a = 52.2 A. b = 64.9 A and c = 100.1 A. Both the monoclinic crystals, which diffract beyond 3.0 A, and the orthorhombic crystals, which diffract beyond 2.5 A, probably have three molecules of 12,400 Da each in the crystallographic asymmetric unit.

Crystallization and preliminary X-ray diffraction analysis of the ArsC protein from the Escherichia coli arsenical resistance plasmid, R773

Diffraction data to 3.0 A resolution were collected on crystals of ArsC protein from the conjugative resistance factor R773 which mediates arsenical resistance in the Gram negative bacterium Escherichia coli. The crystal system is tetragonal, a = 116.2 A, c = 145.0 A and the space group is either P4(1)2(1)2 or P4(3)2(1)2. The most probable range for the contents of the asymmetric unit is four to eight ArsC molecules (M(r) = 15,811).

Teaching airway management on anaesthetised patients

In order to assess the availability of appropriate resources for a programme of in-theatre teaching of airway skills using anaesthetised patients, two surveys of airway management on anaesthetised patients with identification of those suitable for teaching airway care; and a questionnaire to senior anaesthetists assessing attitudes to such teaching were performed. The results demonstrated that, of all patients undergoing general anaesthesia 45% were intubated and of these 29% were regarded as suitable for teaching intubation. The introduction of the Laryngeal Mask Airway (LMA) into clinical practice has reduced the number of patients having their airways maintained by either bag and mask or tracheal intubation, with implications for learning those skills. In our survey 16% had a Laryngeal Mask Airway (LMA) placed for airway securement and of these 29% would have been intubated had the LMA not been available. Finally, amongst anaesthetists in our survey there is a wide variety of attitudes to teaching airway skills using anaesthetised patients.

The occupancy of two distinct conformations by active-site histidine-119 in crystals of ribonuclease is modulated by pH

Structures of a semisynthetic RNase have been obtained to a resolution of 2.0 A at pH values of 5.2, 6.5, 7.5, and 8.8, respectively. The principle structural transformation occurring over this pH range is the conversion of the side chain of active site residue His-119 from one conformation (chi 1 = -43 degrees to -57 degrees) at low pH to another (chi 1 = +159 degrees to +168 degrees) at higher pH values. On the basis of this observation, a model is proposed that reconciles the disparate pK values for His-119 in the enzyme-substrate complex that have been deduced from kinetic studies and from proton NMR measurements in the presence of pseudosubstrates.

Structural investigation of catalytically modified F120L and F120Y semisynthetic ribonucleases

The structures of two catalytically modified semisynthetic RNases obtained by replacing phenylalanine 120 with leucine and tyrosine have been determined and refined at a resolution of 2.0 A (R = 0.161 and 0.184, respectively). These structures have been compared with the refined 1.8-A structure (R = 0.204) of the fully active phenylalanine-containing enzyme (Martin PD, Doscher MS, Edwards BFP, 1987, J Biol Chem 262:15930-15938) and with the catalytically defective D121A (2.0 A, R = 0.172) and D121N (2.0 A, R = 0.186) analogs (deMel VSJ, Martin PD, Doscher MS, Edwards BFP, 1992, J Biol Chem 267:247-256). The movement away from the active site of the loop containing residues 65-72 is seen in all three catalytically defective analogs--F120L, D121A, and D121N--but not in the fully active (or hyperactive) F120Y. The insertion of the phenolic hydroxyl of Tyr 120 into a hydrogen-bonding network involving the hydroxyl group of Ser 123 and a water molecule in F120Y is the likely basis for the hyperactivity toward uridine 2',3'-cyclic phosphate previously found for this analog (Hodges RS, Merrifield RB, 1974, Int J Pept Protein Res 6:397-405) as well as the threefold increase in KM for cytidine 2',3'-cyclic phosphate found for this analog by ourselves.

Prozone phenomenon in secondary syphilis. Has its time arrived?

We present three patients with syphilis in which the prozone phenomenon was present--a very high antibody titer, leading to a false-negative test in undiluted specimens. One of our three patients was positive for human immunodeficiency virus (HIV), another was at risk for HIV infection, and had some clinical findings compatible with HIV infection (this patient was seen before HIV serologic tests were available). We propose that HIV infection, by its B-cell dysregulation, may lead to higher nontreponemal serologic titers, raising the possibility that the prozone phenomenon may be more prevalent in HIV-positive individuals with syphilis than in luetic patients who are negative for HIV.

Crystal structure of the complex of human alpha-thrombin and nonhydrolyzable bifunctional inhibitors, hirutonin-2 and hirutonin-6

The crystal structure of the complexes of hirutonin-2 and hirutonin-6 with human alpha-thrombin have been solved and refined to R-factors of 0.169 (2.0 A resolution) and 0.162 (2.1 A), respectively. Hirutonins belong to a family of bifunctional inhibitors bearing a noncleavable moiety mimicking the scissile bond. Hirutonin-2 is an analog of (D)Phe-Pro-Arg-Gly-hirudin49-65; hirutonin-6 has the same N-terminal tripeptide connected to a shortened fibrinogen exosite-binding part by a short, nonpeptidyl linker. The hirutonin-6 molecule is well defined in the electron density with the exception of the C-terminal Leu-h61. The linker follows near the bottom of the canyon connecting the active site with the exosite, forms a short antiparallel beta-sheet-like arrangement with Leu40-Leu41 and makes van der Waals contacts with Glu39-Leu40-Leu41 of thrombin. In the thrombin-hirutonin-2 complex, the N- and C-terminal parts of the inhibitor are well ordered (except the C-terminal Gln-h65) while the central portion of the linker is partially disordered. The glycine analog in the P1' position of hirutonin-2 assumes a conformation similar to that of the canonical form (Bode and Huber (1992) Eur. J. Biochem. 204:433-451) and supports the identification of the S1' site as restricted by His57, Trp60D, Lys60F, and the Cys42-Cys58 disulfide bridge. The carbonyl oxygen of the P1 arginine residue is located in the oxyanion hole formed by the NH groups of Gly193 and Ser195, while the carbonyl carbon is positioned within a short distance, 2.8 A, from the O gamma of Ser195. This resembles the conformation of the substrate-like inhibitors bound to other serine proteases. The N-terminal (D)Phe-Pro-Arg fragment common to both inhibitors binds to thrombin in a fashion very similar to that of other inhibitors having this motif. The binding of the C-terminus of hirutonins to the fibrinogen-binding exosite is similar to that observed in hirudin and hirulog complexes.