Effects of a hemoglobin-based oxygen carrier (HBOC-201) on coagulation testing

Polymerized bovine hemoglobin (HBOC-201) is currently under investigation as an alternative to blood banked human red cells. Due to the dark red, hemolyzed appearance of HBOC-201, we sought to describe the effects of HBOC-201 on coagulation analyzers that perform prothrombin times (PT), activated partial thromboplastin times, fibrinogen, and antithrombin. Pooled normal plasma was combined with HBOC-201 to achieve plasma hemoglobin levels of 1.4, 2.6 3.8, 4.8, and 6.2 g/dL. Results for each test from HBOC-201 prepared plasmas were compared to saline matched controls. Two consecutive absolute result differences of > 10% between saline controls and HBOC-201 samples were used for determining interference on test accuracy by the concentration of HBOC-201. Mechanical detection methods (fibrometer, STA, CS-190) and the MDA-180 were less affected by increasing levels of HBOC-201 than optical detection devices for all test parameters.

A crucial role of macrophages in the immune responses to oral DNA vaccination against hepatitis B virus in a murine model

In the previous study, we had shown that live oral vaccination with Salmonella typhimurium delivering plasmid DNA-HBsAg (oral DNA vaccine) evoked a vigorous T cell response and a weak antibody response with predominant subclass IgG2a in mice, suggesting a significant involvement by professional antigen presenting cells (APC). In the present study, this possibility was further studied by infecting peritoneal macrophages (MPhi) with the oral DNA vaccine. Although, the infected cells could only express low level of the viral antigen, they nevertheless stimulated a vigorous lymphocyte proliferation of splenocytes from immune mice, induced these cells to elaborate interferon-gamma and stimulated development of HBV-specific cytotoxicity against target cells expressing the viral antigen. Infusion of the infected MPhi evoked a vigorous Th 1 and cytotoxic T lymphocyte (CTL) response and a weak IgG2a antibody response in mice, which was essentially the same as response to the oral DNA vaccine. In contrast, recombinant protein vaccine evoked a vigorous IgG1 antibody response and a weak T cell response. While, given intramuscularly, the same plasmid DNA vaccine as that contained in the oral DNA vaccine evoked a vigorous IgG1 antibody response and a moderate T cell response in these animals. It was concluded that professional APC may orchestrate the immune response to live oral DNA vaccine and it was of interest to note that different vaccine formulation and routes of administration evoke distinct immune response to HBV.

Parathyroidectomy promotes wound healing and prolongs survival in patients with calciphylaxis from secondary hyperparathyroidism

BACKGROUND

Calciphylaxis is a rare but life-threatening condition occasionally affecting patients with secondary hyperparathyroidism. Parathyroidectomy has been advocated as the only potentially curative intervention.

METHODS

Between January 1989 and May 2000, 13 patients with pathologic/clinical criteria of calciphylaxis were treated at our institution. Of these 13 patients, 7 were managed with medical therapy alone, and 6 were referred for parathyroidectomy. The medical records were reviewed, and patients/relatives were interviewed.

RESULTS

All patients had cutaneous wounds requiring local debridement predominantly located on the lower extremities or abdominal wall. Six patients underwent subtotal (3.5 gland) parathyroidectomy without morbidity. All 6 had significant reductions in parathyroid hormone levels after surgery (mean decrease, 94% +/- 0%), and all reported resolution of pain and healing of cutaneous wounds. Of the remaining 7 patients who had medical management alone, 5 eventually died of complications related to calciphylaxis. In comparing the 2 groups, patients who underwent parathyroidectomy had a significantly longer median survival than those who did not have surgery (36 vs 3 months, P =.021).

CONCLUSIONS

Calciphylaxis frequently causes gangrene, sepsis, and eventual death. Parathyroidectomy can be performed with minimal morbidity and is associated with resolution of pain, wound healing, and a significantly longer median survival. Therefore, patients with secondary hyperparathyroidism and signs/symptoms of calciphylaxis should be referred promptly for consideration of parathyroidectomy.

Folic acid supplements during pregnancy and risk of miscarriage

BACKGROUND

Although taking supplements that contain 400 microg of folic acid before and during early pregnancy reduces a woman's risk for having a baby with a neural-tube defect (NTD), the effects of such supplements on other pregnancy outcomes remain unclear. We examined whether the use of such supplements affects the occurrence of miscarriage.

METHODS

Participants were women in China who had taken part in a recent folic acid campaign to prevent NTDs and who had registered in this campaign before they became pregnant for the first time. We examined the risk for miscarriage among women who had confirmed pregnancies and who had or had not taken pills containing only 400 microg of folic acid before and during early pregnancy.

RESULTS

The overall rate of miscarriage was 9.1% (2155/23806). The rates of miscarriage among women who had and had not taken folic acid pills before and during the first trimester were 9.0% and 9.3%, respectively (risk ratio 0.97 [95% CI 0.84-1.12]). The distributions of gestational age at pregnancy diagnosis and at miscarriage were similar for both groups of women.

INTERPRETATION

In this population-based study of a cohort of women whose use of folic acid supplements while pregnant had been previously documented and who had been pregnant for the first time, we found no evidence that daily consumption of 400 microg of folic acid before and during early pregnancy influenced their risk for miscarriage.

Intraoperative positioning for circumferential extremity burns

A technique for intra-operative patient positioning is described which allows circumferential access to burned extremities for prepping and surgery. This technique avoids the need for turning the patient during the operative procedure. In our 13 yr experience, there have been no complications attributed to this technique.

Retinoic acid receptor-independent mechanism of apoptosis of melanoma cells by the retinoid CD437 (AHPN)

Retinoic acid (RA) induces differentiation of S91 melanoma cells through activation of RA receptor (RAR)gamma without affecting cell viability. The novel RARgamma-agonist CD437 (AHPN), however, also induces concomitant apoptosis through an unknown mechanism which was investigated here. By utilizing DNA microarray analysis, five apoptosis-associated, CD437-induced transcripts (CITs) were identified. Interestingly, all CITs are also regulated by p53 in a DNA damage response, and consistent with this interpretation, CD437 was found to cause DNA adduct-formation. However, p53 is not required for CD437-dependent regulation of CITs. Among this set of genes, induction of p21(WAF1/CIP1) is likely to be responsible for early S-phase growth-arrest of CD437-treated cells, whereas ei24 is a critical mediator of CD437-induced apoptosis in S91 cells. These data suggest an RAR-independent mechanism in which CD437 causes DNA adduct-formation, resulting in induction of a p53-independent DNA damage response, and subsequent growth-arrest and apoptosis. CD437-mediated DNA adduct-formation may also explain its apoptotic effects in other cell types.

Pharmacodynamics induced by direct electric current for the treatment of 5-fluorouracil resistant tumor: an animal experiment

The repeated use of chemotherapy to treat patients with colorectal carcinoma may be limited by the fact it creates resistance cells. However, we have observed a remarkable decrease in certain types of drug resistance in patients treated with direct electric current. Experimental studies were therefore performed in animals to determine the differences in pharmacodynamics between chemotherapy with and that without electric treatment. Tumors were created in BALB/c mice by intradermal injection of 0.25 ml 4 x 10(6) Colon 26 cells/ml in the abdomen. Seven days later the mice were divided into two groups: controls and those that underwent electric treatment. Direct electric current (1,000 V, 0.2-0.8 microA) was passed between a platinum electrode inserted intradermally and the earth during and for 1 h after a single intravenous injection of 5-fluorouracil (5-FU; 12.5 mg ml(-1) kg(-1)). Peripheral blood samples were collected before and 5, 10, 20, 30, 45, and 60 min after the injection of 5-FU. Concentrations of 5-FU in the sera and tissues were measured by HPLC. The intratumoral concentrations of 5-FU in the electric treatment group were higher than those in the controls (P<0.05, two-factor analysis of variance), but the serum concentrations were not statistically different between the two groups. Pharmacodynamic changes were thus observed as a result of electrostatic treatment during chemotherapy. This elevated 5-FU concentration in the tumor tissue is considered one of the reasons for the effective inhibition of 5-FU resistance in clinical cases.

The combined effect of isolation and Fasciola hepatica infection on the life history traits of Fossaria cubensis

Life history traits of Fossaria cubensis were compared between isolated and paired snails after infection with three miracidia of Fasciola hepatica. Four experimental groups were tested: isolated-unexposed, paired-unexposed, isolated-infected, and paired-infected. A repeated-measures ANOVA showed statistically significant interactions among isolation, infection, and age effects for shell size, number of egg masses per snail, number of eggs per snail, and number of viable eggs per snail. Isolated-unexposed snails exhibited the higher values of these variables and those of survival and finite and intrinsic rates of natural increase. Infection stimulated shell growth during the prepatent period, but differences were present only in paired snails since isolation causes a similar effect. Reproduction, in terms of the number of egg masses per snail and the number of eggs per mass per snail, decreases in the presence of parasitic infection, whereas isolation stimulates it. These effects were observed from early stages of infection.

Newly developed drug delivery system in cancer chemotherapy using direct electric current

To improve the antitumor effect of chemotherapy on a target organ, we experimentally investigated pharmacokinetic alteration of methotrexate (MTX) induced by an electric current in rats to ascertain whether the local concentration of MTX could be enhanced while reducing the concentration in blood. Six male Wistar rats had platinum electrodes introduced into both kidneys. Three rats were subjected to direct current (3.5 V, 50 microA) for 3 hours, while another three control rats received no current. While providing the current to the treated group, all of the rats were intravenously injected with MTX at a dose of 1 mg/kg. The MTX concentration in urine (excreted from each ureter) and serum was measured by fluorescence polarization immunoassay. Cumulative MTX renal excretion rate was significantly higher in the cathode than anode side in the treated group (p < 0.01). Serum MTX concentration at 0 to 5 min was significantly reduced in the treated group (p < 0.03). The first part of the area under the curve (i.e., alpha curve) was markedly increased in the treated group versus controls (p = 0.05). Electric therapy using a slight direct current could gather anionized MTX to the cathode, while reducing MTX concentration in the serum of experimental rats.

PIES, a protein interaction extraction system

We consider the problem of extracting, manipulating, and managing biological pathways, especially protein-protein interaction pathways. We discuss here the Protein Interaction Extraction System (PIES). PIES is contructed on top of three main technologies: Kleisli, BioNLP, and Graphviz. Kleisli is a broad-scale data integration system that we use for downloading Medline abstracts and for general manipulation and management of pathway/interaction databases. BioNLP is a natural language-based information extraction module that we use for analysing Medline abstracts and to extract precise protein-protein and other interaction information. Graphviz is a graphical layout package developed for directed graphs that we use for visualization of the extracted pathways. PIES can be augmented with various means for extracting protein interaction information from sequence databases, for example, by using Kleisli's power to integrate sequence comparison tools to detect gene fusion events in sequence databases.

Redox control of retinoic acid receptor activity: a novel mechanism for retinoic acid resistance in melanoma cells

Retinoic acid (RA) slows growth and induces differentiation of tumor cells through activation of RA receptors (RARs). However, melanoma cell lines display highly variable responsiveness to RA, which is a poorly understood phenomenon. By using Northern and Western blot analyses, we show that RA-resistant A375 and RA-responsive S91 melanoma cells express comparable levels of major components of RAR-signaling pathways. However, A375 cells have substantially higher intracellular reactive oxygen species (ROS) levels than S91 cells. Lowering ROS levels in A375 cells through hypoxic culture conditions restores RAR-dependent trans-activity, which could be further enhanced by addition of the antioxidant N-acetyl-cysteine. Hypoxia also enhances RAR activity in the moderately RA-responsive C32 cells, which have intermediate ROS levels. Conversely, increasing oxidative stress in highly RA-responsive S91 and B16 cells, which have low ROS levels, by treatment with H(2)O(2) impairs RAR activity. Consistent with these observations, RA more potently inhibited the proliferation of hypoxic A375 cells than that of normoxic cells. Oxidative states diminish, whereas reducing conditions enhance, DNA binding of retinoid X receptor/RAR heterodimers in vitro, providing a molecular basis for the observed inverse correlation between RAR activity and ROS levels. The redox state of melanoma cells provides a novel, epigenetic control mechanism of RAR activity and RA resistance.

A comparison of human dental plaque microcosm biofilms grown in an undefined medium and a chemically defined artificial saliva

The growth and pathogenic properties of dental plaque result from interactions between the microbiota and the oral environment and have been studied in laboratory experimental systems ranging from single or a few species (such as in chemostats) to dental plaque microcosms. Microcosm plaque is an in vitro version of natural plaque and has been explored as a microflora model because it is sited a more manipulable and controllable environment. It is obtained as microcosm biofilms in an 'artificial mouth' plaque culture system by culturing the bacteria in natural plaque-enriched saliva (i.e. salivary bacteria where a whole-saliva donor has abstained from oral hygiene for 24 h to increase the plaque bacteria in the saliva). The aim here was to examine whether a new, chemically defined analogue of saliva (defined medium mucin, DMM) could substitute for a previously used, chemically undefined medium (basal medium mucin, BMM) as an analogue of saliva for large-scale biofilm culturing. DMM contains various ions, mucin, amino acids, vitamins and growth factors at concentrations generally similar to those in saliva, whereas BMM contains yeast extract, peptones and mucin. To model the nutrient functions of salivary proteins, amino acids equivalent to 5 g/l casein were also included in DMM. In earlier studies, BMM-grown plaques were similar to natural plaques in structure, composition, growth rate and pH response to substrates. Their doubling-time patterns over a 20-day period were similar, except that the DMM-grown plaques showed biphasic growth patterns that were more pronounced than with BMM. Variation in enzyme profiles between BMM- and DMM-grown plaque, measured using the API-ZYM technique, provided evidence of nutritional effects on plaque composition. It was concluded that realistic growth rates and patterns are generated in microcosm plaque biofilms by supplying both DMM and BMM. However, the use of DMM enables specific modifications to be made to nutrient conditions during large-scale culture in our 'artificial mouth' biofilm system.

Epidermal growth factor (EGF) receptor kinase-independent signaling by EGF

The ErbB family of receptors, which includes the epidermal growth factor receptor (EGFR), ErbB2, ErbB3, and ErbB4, mediate signaling by EGF-like polypeptides. To better understand the role of the EGFR tyrosine kinase, we analyzed signaling by a kinase-inactive EGFR (K721M) in ErbB-devoid 32D cells. K721M alone exhibited no detectable signaling capacity, whereas coexpression of K721M with ErbB2, but not ErbB3 or ErbB4, resulted in EGF-dependent mitogen-activated protein kinase (MAPK) activation. The kinase activity, but not tyrosine phosphorylation, of ErbB2 was required for EGF-induced MAPK activation. The presence of tyrosine phosphorylation sites in K721M was not a requisite for signaling, indicating that transphosphorylation of K721M by ErbB2 was not an essential mechanism of receptor activation. Conversely, the mutated kinase domain of K721M (residues 648-973) and tyrosine phosphorylation of at least one of the receptors were necessary. EGF was found to activate the pro-survival protein kinase Akt in stable cell lines expressing K721M and ErbB2 but, unlike cells expressing wild-type EGFR, was incapable of activating signal transducers and activators of transcription (STAT) or driving cell proliferation. These results demonstrate that EGFR-ErbB2 oligomers are potent activators of MAPK and Akt, and this signaling does not require EGFR kinase activity.

Intercostal Neuromas: A Treatable Cause of Postoperative Breast Surgery Pain

Patients presenting with pain after breast surgery were selected to undergo resection of intercostal neuromas. The patients had localized Tinel's signs at one or more intercostal nerves at the lateral chest wall with radiation in the distribution of the pain. Patients also responded to diagnostic injections of local anesthetic. The patients were felt to have pain not related to breast implants and capsular contracture or intercostobrachial nerve injury. Neuromas were found in all patients meeting these requirements. Surgical resection resulted in complete pain relief. Diagnosis of this entity and consideration of surgical treatment may be underrecognized.

Prolonged, symptomatic hypocalcemia with pamidronate administration and subclinical hypoparathyroidism

A 62-yr-old woman with thyroid carcinoma metastatic to bone, and a history of subclinical hypoparathyroidism was admitted to the hospital in hypocalcemic crisis 5 wk after receiving iv pamidronate. The patient had tetany and laryngospasm. An electrocardiogram showed junctional rhythm with QT segment prolongation. The patient had previously maintained a low-normal serum calcium on 500-750 mg of calcium carbonate and 600 IU of vitamin D daily. One week after pamidronate administration the patient's calcium and vitamin D supplementation were inadvertently discontinued. She continued to take daily intranasal calcitonin. At the time of her hospitalization for hypocalcemia, the patient's serum calcium was 4.3 mg/dL. The patient received aggressive calcium and vitamin D supplementation. However, her serum calcium remained below 6 mg/dL for a 2-wk period, and took another week to return to the normal range. In this article, we discuss the counterregulatory responses necessary to maintain calcium homeostasis following osteoclast inhibition by bisphosphonates. We also review the risk factors for hypocalcemia following bisphosphonate administration. Pamidronate and other bisphosphonates are becoming an integral part of the management of normocalcemic patients with malignant bone disease. Therefore, awareness of risk factors for hypocalcemia and familiarity with avenues available for protection from potentially catastrophic hypocalcemia are both crucial.

Children with persistent conduct problems who dropout of treatment

Dropout of treatment is one of the key issues in outcome in a child and adolescent mental health service. We report two studies focusing on the treatment process and the dropout rate of children with persistent conduct problems presenting to a community mental health service, using a prospective design. The first study included 32 children and used a randomised controlled treatment design comparing a CBT approach with conjoint family therapy and an eclectic approach. The overall dropout rate was 36%. Dropout occurred significantly less frequently in the CBT group. The dropout group was associated with mothers who were younger and less educated, a poorer rating by the clinicians at the last meeting, parental dissatisfaction with the treatment service and perception that the treatment was less organised and having less behavioural tasks. In the second study we used a naturalistic follow-up design. Forty-six children were included. The overall dropout rate was 48%. Again, the children who defaulted were rated by clinicians as less likely to have improved and dropout was also significantly associated with parental perception of a less organised treatment. In both studies dropout usually occurred after assessment and at the early phase of treatment.

Effects of retinoic acid and sodium butyrate on gene expression, histone acetylation and inhibition of proliferation of melanoma cells

Retinoic acid (RA) induces growth-arrest of many tumor cell lines but it is an ineffective therapeutic against melanoma. We investigated whether the histone deacetylase (HDAC)-inhibitor sodium butyrate (BUT) can restore or potentiate the RA-response of RA-resistant human A375, and RA-responsive S91 murine melanoma cells. BUT induced expression of RARbeta and p21(waf1/cip1) mRNA in A375 cells but in S91 cells only p21(waf1/cip1) was induced. RA and BUT synergistically activated transcription of an RA-dependent reporter gene in S91, but not A375 cells. BUT increased histone H4-acetylation in both cell types. RA potentiated BUT-mediated inhibition of S91 cell proliferation, whereas A375 cells remained largely resistant to both compounds. HDAC-inhibitors may enhance the activity of RA on RA-responsive melanoma cells.

Efficacy and cognitive effects of right unilateral electroconvulsive therapy

The efficacy, memory, and cognitive effects of right unilateral (RUL) electroconvulsive therapy (ECT) at 2.5 times threshold in 32 inpatients with moderate to severe major depressive disorder were evaluated at baseline, during the course of treatment, and 1 month after treatment. Neuropsychological assessment included the Randt Memory Test, Personal Memory Test, short-version Wechsler Adult Intelligence Scale-Revised, and Self-Rating Scale of Memory Functions. At the treatment end point, although the Hamilton Depression Rating Scale mean score was decreased by 54.2%. the response rate of 2.5 times threshold RUL ECT using stringent criteria was only 31.2%. Treatment was associated with significant anterograde memory impairment in the short term. Mean total scores of the Randt Memory Test and Personal Memory Test were decreased from baseline by 14.8% and 32.5%, respectively, after six sessions of ECT. These memory deficits were significantly improved by the 1 month follow-up examination. Subjective memory scores increased consistently during treatment, correlating with improvements in mood. No adverse effects on nonmemory cognition were found. Although RUL ECT at 2.5 times threshold is not associated with marked or persistent cognitive disturbances, its efficacy may be insufficient in clinical practice.

Survivin and the inner centromere protein INCENP show similar cell-cycle localization and gene knockout phenotype

BACKGROUND

Survivin is a mammalian protein that carries a motif typical of the inhibitor of apoptosis (IAP)proteins, first identified in baculoviruses. Although baculoviral IAP proteins regulate cell death, the yeast Survivin homolog Bir1 is involved in cell division. To determine the function of Survivin in mammals, we analyzed the pattern of localization of Survivin protein during the cell cycle, and deleted its gene by homologous recombination in mice.

RESULTS

In human cells, Survivin appeared first on centromeres bound to a novel para-polar axis during prophase/metaphase, relocated to the spindle midzone during anaphase/telophase, and disappeared at the end of telophase. In the mouse, Survivin was required for mitosis during development. Null embryos showed disrupted microtubule formation, became polyploid, and failed to survive beyond 4.5days post coitum. This phenotype, and the cell-cycle localization of Survivin, resembled closely those of INCENP. Because the yeast homolog of INCENP, Sli15, regulates the Aurora kinase homolog Ipl1p, and the yeast Survivin homolog Bir1 binds to Ndc10p, a substrate of Ipl1p, yeast Survivin, INCENP and Aurora homologs function in concert during cell division.

CONCLUSIONS

In vertebrates, Survivin and INCENP have related roles in mitosis, coordinating events such as microtubule organization, cleavage-furrow formation and cytokinesis. Like their yeast homologs Bir1 and Sli15, they may also act together with the Aurora kinase.

Attitudes on organ donation among Hawaii physicians

A survey of physicians attending the recent Hawaii Medical Association meeting was conducted in order to assess physician attitudes on organ donation. Physicians were asked 6 questions and demographics were collected. Results indicate that Hawaii physicians generally support organ donation and are aware of some of the current federal legislation regarding donation.

Well-defined sulfobetaine-based statistical copolymers as potential antibioadherent coatings

The potential use of novel poly(sulfobetaine) copolymers as antibioadherent coatings was investigated using Pseudomonas aeruginosa as a model microorganism and human macrophages and 3T3 mouse embryonic fibroblasts. Two well-defined statistical copolymers with narrow molecular weight distributions were prepared by group transfer copolymerization of n-butyl methacrylate (nBuMA) with either 10 or 30 mol % 2-(dimethylamino)ethyl methacrylate (DMAEMA). Sulfobetainized nBuMA-DMAEMA copolymers (poly[sulfobetaine-stat-nBuMA]) were obtained by treating these precursor polymers with 1,3-propanesultone under mild conditions. Both proton NMR spectroscopy and elemental microanalyses indicated that essentially all the DMAEMA residues were derivatized in both copolymers. Poly(methyl methacrylate) (PMMA) discs were coated with the sulfobetainized nBuMA-DMAEMA copolymers and the bioadherent properties of these coated materials were compared with those of PMMA. Statistically significantly fewer (p<.05) bacteria, macrophages, and fibroblasts adhered to the poly(sulfobetaine-stat-nBuMA)-coated PMMA than to the uncoated PMMA. The poly(sulfobetaine-stat-nBuMA) copolymer containing the higher proportion (30 mol %) sulfobetainized DMAEMA residues proved to be the more effective antibioadherent coating. The antibioadherent properties of these coating materials may allow the cost-effective production of dirt-resistant, easy to clean work surfaces, bioinert coatings for medical devices, and antifouling coatings for marine, agricultural, and industrial applications.

Carboxy terminus of human herpesvirus 8 latency-associated nuclear antigen mediates dimerization, transcriptional repression, and targeting to nuclear bodies

Human herpesvirus 8 (HHV-8; also known as Kaposi's sarcoma-associated herpesvirus) is the causative agent of Kaposi's sarcoma and certain B-cell lymphomas. In most infected cells, HHV-8 establishes a latent infection characterized by the expression of latency-associated nuclear antigen (LANA) encoded by open reading frame 73. Although unrelated by sequence, there are functional similarities between LANA and the EBNA-1 protein of Epstein-Barr virus. Both accumulate as subnuclear speckles and are required for maintenance of the viral episome. EBNA-1 also regulates viral gene expression and is required for cell immortalization, suggesting that LANA performs similar functions in the context of HHV-8 infection. Here we show that LANA forms stable dimers, or possibly higher-order multimers, and that this is mediated by a conserved region in the C terminus. By expressing a series of truncations, we show that both the N- and C-terminal regions localize to the nucleus, although only the C terminus accumulates as nuclear speckles characteristic of the intact protein. Lastly, we show that LANA can function as a potent transcriptional repressor when tethered to constitutively active promoters via a heterologous DNA-binding domain. Domains in both the N and C termini mediate repression. This suggests that one function of LANA is to suppress the expression of the viral lytic genes or cellular genes involved in the antiviral response.

Probing the active center gorge of acetylcholinesterase by fluorophores linked to substituted cysteines

To examine the influence of individual side chains in governing rates of ligand entry into the active center gorge of acetylcholinesterase and to characterize the dynamics and immediate environment of these residues, we have conjugated reactive groups with selected charge and fluorescence characteristics to cysteines substituted by mutagenesis at specific positions on the enzyme. Insertion of side chains larger than in the native tyrosine at position 124 near the constriction point of the active site gorge confers steric hindrance to affect maximum catalytic throughput (k(cat)/K(m)) and rates of diffusional entry of trifluoroketones to the active center. Smaller groups appear not to present steric constraints to entry; however, cationic side chains selectively and markedly reduce cation ligand entry through electrostatic repulsion in the gorge. The influence of side chain modification on ligand kinetics has been correlated with spectroscopic characteristics of fluorescent side chains and their capacity to influence the binding of a peptide, fasciculin, which inhibits catalysis peripherally by sealing the mouth of the gorge. Acrylodan conjugated to cysteine was substituted for tyrosine at position 124 within the gorge, for histidine 287 on the surface adjacent to the gorge and for alanine 262 on a mobile loop distal to the gorge. The 124 position reveals the most hydrophobic environment and the largest hypsochromic shift of the emission maximum with fasciculin binding. This finding likely reflects a sandwiching of the acrylodan in the complex with the tip of fasciculin loop II. An intermediate spectral shift is found for the 287 position, consistent with partial occlusion by loops II and III of fasciculin in the complex. Spectroscopic properties of the acrylodan at the 262 position are unaltered by fasciculin addition. Hence, combined spectroscopic and kinetic analyses reveal distinguishing characteristics in various regions of acetylcholinesterase that influence ligand association.