Comprehensive Analysis of Risk Factors for Bronchopulmonary Dysplasia in Preterm Infants in Taiwan: A Four-Year Study

Bronchopulmonary dysplasia (BPD) is a major respiratory condition mainly affecting premature infants. Although its occurrence is global, risk factors may differ regionally. This study, involving 3111 infants with birth weight ≤ 1500 gm or gestational age (GA) < 30 weeks, aimed to identify risk factors for BPD and BPD/mortality in Taiwan using data from the Taiwan Neonatal Network. The BPD criteria were based on the National Institute of Child Health and Human Development standards. Average GA was 27.5 weeks, with 23.7% classified as small for GA (SGA). Multivariate analysis highlighted low GA, low birth weight, and other perinatal factors as significant risk indicators for BPD. For moderate-to-severe BPD, additional risk factors included male gender and SGA, endotracheal intubation (ETT) or cardiopulmonary cerebral resuscitation (CPCR) in initial resuscitation. In the moderate-to-severe BPD/death group, SGA and ETT or CPCR in initial resuscitation remained the only additional risk factors. The study pinpoints male gender, SGA and ETT or CPCR as key risk factors for moderate-to-severe BPD/death in low-birth-weight infants in Taiwan, offering a basis for focused interventions and further research.

Changing patterns of infectious diseases in children during the COVID-19 pandemic

Each infectious disease has had its own epidemic pattern and seasonality for decades. However, public health mitigation measures during the coronavirus disease 2019 (COVID-19) pandemic have resulted in changing epidemic patterns of infectious diseases. Stringent measures resulted in low incidences of various infectious diseases during the outbreak of COVID-19, including influenza, respiratory syncytial virus, pneumococcus, enterovirus, and parainfluenza. Owing to the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and subsequent immunity development, decreasing virulence of SARS-CoV-2, and worldwide immunization against SARS-CoV-2 in children beyond 6 months of age, mitigation measures are lifted country by country. Consequently, the immunity debt to infectious respiratory viruses other than SARS-CoV-2 contributed to the "off-season," "see-saw," and "upsurge" patterns of various infectious diseases in children. Moreover, apart from the persistence of SARS-CoV-2, the coexistence of other circulating viruses or bacterial outbreaks may lead to twindemics or tripledemics during the following years. Therefore, it is necessary to maintain hand hygiene and immunization policies against various pathogens to alleviate the ongoing impact of infectious diseases on children.

Phthalate Exposure Pattern in Breast Milk within a Six-Month Postpartum Time in Southern Taiwan

Di-(2-ethylhexyl) phthalate (DEHP), a common plasticizer, has been detected in breast milk in many countries; however, whether phthalate metabolite concentration and the detection rate in breast milk change postpartum is still unknown. We measured phthalate metabolite concentrations in breast milk in the first 6 months postpartum in women enrolled in the E-Da hospital from January to July 2017. A total of 56 breastfeeding mothers and 66 samples were included in this study. We analyzed the samples’ concentration of eight phthalate metabolites using liquid chromatography mass spectrometry. The concentration of mono-2-ethylhexyl phthalate (MEHP) was significantly higher in the first month, and then decreased over time. The detection rate of ono-isobutyl phthalate (MiBP) and mono-n-butyl phthalate (MBP) was low in the first month and then increased over time. Compared with a previous study published in 2011, the levels of MEHP and MiBP in breast milk were much lower in the present study, suggesting an increased awareness of the health risks of phthalate exposure after a food scandal occurred in Taiwan. This study provides information for evaluating newborns’ exposure to different kinds of phthalate through human milk in the postpartum period.

High correlation between human rhinovirus type C and children with asthma exacerbations in Taiwan

BACKGROUND/PURPOSES

Human rhinovirus type C (HRV-C) has been associated with asthma exacerbation (AE) in children in several countries. However, in Taiwan the association between HRV, especially HRV-C, and AE in children has yet to be elucidated. We sought to investigate the prevalence of respiratory viruses in children with acute lower respiratory tract infection (ALRTI) in Taiwan and the association between different types of HRV and AE in children.

METHODS

This prospective study was conducted from 2011 to 2013, and enrolled children with ALRTI, including an asthma exacerbation group (AE; n = 28) and a Non-asthma group (n = 66). Viruses were detected by culture, reverse transcription-polymerase chain reaction, and molecular sequencing of nasopharyngeal swabs.

RESULTS

The prevalence of identified respiratory viruses was 78.6% in the AE group and 65.2% in the Non-asthma group. The prevalence rates of HRV and HRV-C were significantly higher in the AE group than in the Non-asthma group (67.9% vs. 33.3% in HRV, p = 0.002; and 50% vs. 15.2% in HRV-C, p < 0.001). Among the children with HRV, the prevalence of HRV-C (68.4%) was higher than that of the other types of HRV (31.6%, including HRV-A 26.3%, and HRV-B 5.3%) in the AE group but not in the Non-asthma group (40.9% vs. 59.1%).

CONCLUSIONS

HRV is the most predominant viral infection responsible for pediatric AE in Taiwan, and HRV-C is responsible for more of these exacerbations than HRV-A or HRV-B.

The beneficial effect of air cleanliness with ISO 14644-1 class 7 for surgical intervention in a neonatal intensive care unit: A 10-year experience

Whether critically ill neonates needing a surgical intervention should be transferred to an operating room (OR) or receive the intervention in a neonatal intensive care unit (NICU) is controversial. In this study, we report our experience in performing surgical procedures in a NICU including air cleanliness.This was a retrospective study performed at a metropolitan hospital. The charts of all neonates undergoing surgical procedures in the NICU and OR were retrospectively reviewed from January 2007 to June 2017. Data on baseline characteristics, procedure and duration of surgery, ventilator use, hypothermia, instrument dislocations, surgery-related infections and complications, and outcomes were analyzed.Ninety-two neonates were enrolled in this study, including 44 in the NICU group and 48 in the OR group. The air cleanliness was International Organization for Standardization (ISO) 14644-1 class 7 in the NICU and class 5-6 in the OR. The NICU group had a younger gestational age and lower birth body weight than the OR group. The OR group had a higher incidence of hypothermia than in the NICU group (56.3% vs 9.1%, P < .001). However, there were no significant differences in surgical site related infections or mortality between the 2 groups.This study suggests that performing surgical procedures in a NICU with air cleanliness class 7 is as safe as in an OR, as least in part, when performing patent ductus arteriosus ligation and exploratory laparotomy.

Resveratrol induces sumoylated COX-2-dependent anti-proliferation in human prostate cancer LNCaP cells

Cyclooxygenase (COX)-2 has been implicated in cancer development. However, resveratrol-induced nuclear accumulation of COX-2 enhances p53-dependent anti-proliferation in different types of cancers. Treatment with resveratrol leads to phosphorylation and nuclear translocation of mitogen-activated protein kinase (ERK1/2), and accumulation of nuclear COX-2 to complex with pERK1/2 and p53. The consequence is Ser-15 phosphorylation of p53 (pSer15-p53), and induction of anti-proliferation in cancer cells. We investigated the mechanisms by which resveratrol-inducible COX-2 facilitates p53-dependent anti-proliferation in prostate cancer LNCaP cells. Resveratrol treatment caused nuclear accumulation and complexing of ERK1/2, pSer15-p53 and COX-2 which was activated ERK1/2-dependent. Knockdown of SUMO-1 by shRNA also reduced nuclear accumulation of COX-2. Inhibition of nuclear accumulation by the COX-2 specific inhibitor, NS-398, inhibited co-localization of nuclear COX-2 and SUMO-1. Similar results were observed in the PD98059-treated cells. Finally, inhibition of SUMO-1 expression also reduced resveratrol-induced expression of pro-apoptotic genes but increased the expression of proliferative genes. In summary, these results demonstrate that inducible COX-2 associates with phosphorylated ERK1/2 to induce the phosphorylation of Ser-15 in p53 and then complexes with p53 and SUMO-1 which binds to p53-responsive pro-apoptotic genes to enhance their expression. The inhibition of COX-2 expression and activity significantly blocks the pro-apoptotic effect of resveratrol.

Pseudomonas aeruginosa infective endocarditis in patients who do not use intravenous drugs: Analysis of risk factors and treatment outcomes

BACKGROUND

Infective endocarditis (IE) due to Pseudomonas aeruginosa is rare and accounts for only about 3% of all patients with this disease. Most infections are associated with the use of intravenous drugs. Patients with P. aeruginosa-related IE who do not use intravenous drugs are extremely rare. We carried out a review of the literature to identify the nature and risk factors of this disease.

METHODS

Patients with IE reported between 1993 and 2013 were reviewed by searching the Medline database using the keywords "endocarditis" and "Pseudomonas aeruginosa". All of the patients included met the definition of the modified Duke criteria.

RESULTS

Twenty-seven patients in 22 reports were reviewed. IE associated with health care accounted for 20 patients (74%). The mean age of the patients was 53.4 years and there was a predominance of men (81.5%). Native valve endocarditis was seen in 20 (74.1%) patients. Surgery for infection control was performed in 15 (55.6%) patients and the mortality rate in patients who underwent surgery was 33.3% (five patients). A relapse of IE after adequate treatment was seen in nine (33.3%) patients. The mortality rate in all 27 patients was 28.6% (2/7) for those with community-acquired IE and 40% (8/20) for those with IE associated with health care. Univariate analysis showed a higher mortality rate in patients aged >60 years and in those whose source of endocarditis was related to a prosthetic device.

CONCLUSION

P. aeruginosa endocarditis has substantial morbidity and mortality. It is characterized by easy relapse and is highly associated with prosthetic devices.

Comparisons of etiology and diagnostic tools of lower respiratory tract infections in hospitalized young children in Southern Taiwan in two seasons

BACKGROUND

Lower respiratory tract infections (LRTIs) play an important role in pediatric diseases; however, there are limited data about LRTIs in Southern Taiwan. This study aimed to investigate the clinical and epidemiological data of LRTIs in this area.

METHODS

Children aged under 5 years who were hospitalized at a medical center in Southern Taiwan with acute LRTIs from July 2010 to October 2010 (summer) and from March 2011 to May 2011 (spring) were prospectively enrolled. Nasopharyngeal aspirates were obtained and sent for viral cultures, multiplex polymerase chain reaction (PCR), and traditional quick tests. The clinical features, laboratory data, and imaging findings were recorded and analyzed.

RESULTS

A total of 90 children were enrolled, 70 of whom had detectable pathogens. The positive rate of conventional viral and bacterial cultures was 25.6%, which increased to 77.77% after combining with the two multiplex PCR methods. Adenovirus and enterovirus were the most common viral etiologies identified (26.5% of cases) and Streptococcus pneumoniae was the leading bacterial etiology (46.4%). The seasonal trend of viral infections in Southern Taiwan was different from Northern Taiwan. There were no differences in demographic data, severity of disease, or hospital stay between single and mixed infections. A similar result was found between nonpneumococcal and pneumococcal infections.

CONCLUSION

Viral infections were the main etiologies of LRTIs in young children. Multiplex PCR methods are rapid assays that can increase the diagnostic yield rate. Mixed infections do not seem to affect the severity of disease. Early detection may aid clinicians in appropriate decision-making and treatment.

Definitive assignment of proton selectivity and attoampere unitary current to the M2 ion channel protein of influenza A virus

The viral ion channel protein M2 supports the transit of influenza virus and its glycoproteins through acidic compartments of the cell. M2 conducts endosomal protons into the virion to initiate uncoating and, by equilibrating the pH at trans-Golgi membranes, preserves the native conformation of acid-sensitive viral hemagglutinin. The exceptionally low conductance of the M2 channel thwarted resolution of single channels by electrophysiological techniques. Assays of liposome-reconstituted M2 yielded the average unitary channel current of the M2 tetramer--1.2 aA (1.2 x 10(-18) A) at neutral pH and 2.7 to 4.1 aA at pH 5.7--which activates the channel. Extrapolation to physiological temperature predicts 4.8 and 40 aA, respectively, and a unitary conductance of 0.03 versus 0.4 fS. This minute activity, below previous estimates, appears sufficient for virus reproduction, but low enough to avert abortive cytotoxicity. The unitary permeability of M2 was within the range reported for other proton channels. To address the ion selectivity of M2, we exploited the coupling of ionic influx and efflux in sealed liposomes. Metal ion fluxes were monitored by proton counterflow, employing a pH probe 1,000 times more sensitive than available Na+ or K+ probes. Even low-pH-activated M2 did not conduct Na+ and K+. The proton selectivity of M2 was estimated to be at least 3 x 10(6) (over sodium or potassium ions), in agreement with electrophysiological studies. The stringent proton selectivity of M2 suggests that the cytopathology of influenza virus does not involve direct perturbation of cellular sodium or potassium gradients.

Urinary N-acetyl-beta-glucosaminidase as an indicator of renal dysfunction in electroplating workers

OBJECTIVES

To investigate chromium-induced renal dysfunction in electroplating workers.

METHODS

A cross-sectional study was used to evaluate four biochemical markers of renal function. A total of 178 workers were divided into 3 comparable groups consisting of 34 hard-chrome plating workers, 98 nickel-chrome electroplating workers. and 46 aluminum anode-oxidation workers, who represented the reference group. Ambient and biological monitoring of urinary chromium were performed to measure exposure concentrations.

RESULTS

Overall, urinary chromium concentrations were highest among hard-chrome plating workers (geometric mean 2.44 microg/g creatinine), followed by nickel-chrome electroplating workers (0.31 microg/g creatinine) and aluminum workers (0.09 microg/g creatinine). Airborne chromium concentrations were also highest in the hard-chrome plating area (geometric mean 4.20 microg/m3), followed by the nickel-chrome electroplating area (0.58 microg/m3) and the aluminum area (0.43 microg/m3). A positive correlation was found between urinary chromium and airborne concentrations (r=0.54, P < 0.01). Urinary concentrations of N-acetyl-beta-D-glucosaminidase (NAG) were also highest among hard-chrome plating workers (geometric mean 4.9 IU/g creatinine), followed by nickel-chrome workers (3.4 IU/g creatinine) and aluminum workers (2.9 IU/g creatinine). The prevalence of "elevated" NAG (>7 IU/g creatinine) was significantly highest among hard-chrome plating workers (23.5%), then among nickel-chrome workers (7.1%) and aluminum workers (8.7%). Differences in beta2-microglobulin, total protein, and microalbumin were not significant.

CONCLUSION

The author's evidence indicates that NAG is an early indicator of renal dysfunction in hard-chrome plating workers.

Nasal septum lesions and lung function in workers exposed to chromic acid in electroplating factories

The objective of this study was to compare workers from chromium, nickel-chromium, and zinc electroplating factories with regards to nasal septum lesions and lung function. Also investigated was the relationship between chromium levels in air and urine. A total of 189 workers from 11 electroplating factories (three chromium, six nickel-chromium, two zinc) were chosen from central Taiwan. All subjects were interviewed by constructed-questionnaire, given a nasal examination by a certified otolaryngologist and a lung function test. In the chromium factories 30.8% of the workers showed evidence of nasal septum perforations and 38.5% showed evidence of nasal septum ulcers. A Mantel extension test for trend showed that workers in the chromium factories were 31.7 times more likely to experience nasal ulcers than nickel-chromium and zinc factory workers. Those who worked in the electroplating tank area were 4.2 times more likely to experience ulcers and those with over 9 years' experience were 30.8 times more likely. A comparison of lung function adjusted for age, gender and smoking habit among workers showed that vital capacity (VC), forced vital capacity (FVC), and forced expiratory volume in 1 s (FEV1) were all significantly decreased among chromium factory workers. Because the results showed that the workers' health is being severely damaged by the harmful environment of chromium electroplating factories, the authors wish to suggest improvements in the workplace are vitally needed to ensure the safety of the workers.

Different modes of inhibition by adamantane amine derivatives and natural polyamines of the functionally reconstituted influenza virus M2 proton channel protein

The influenza virus M2 protein, target of the antiviral drugs amantadine and rimantadine, forms a proton channel which functions during virus uncoating and maturation by modifying the pH in virions as well as in trans-Golgi vesicles. We studied the influence of different ionic gradients on the inhibition of the proton translocation activity of isolated, baculovirus-expressed M2 protein reconstituted into liposomes. Two distinct patterns of inhibition were observed. A group of amphiphilic amines including amantadine, cyclooctylamine and rimantadine inhibited M2 effectively in the presence of physiological Na+ concentrations. The 10-fold greater activity of rimantadine over amantadine and the 100-fold stronger effect of cyclooctylamine compared to cyclopentylamine matched the relative activities in influenza virus-infected cells. A completely different inhibitory pattern emerged for the polyamines spermine, spermidine and putrescine. Polyamines have recently been identified as the 'intrinsic' rectifiers of a class of potassium channels and shown to interact with acidic amino acid residues lining and flanking the channel pore. In the presence of a physiological Na+/K+ gradient their minimal inhibitory concentrations for influenza virus M2 protein were 100, 400 and 500 microM, polyamine levels reported to exist in oocytes. In conditions depleted for Na+, polyamines inhibited M2 at concentrations two to three orders of magnitude lower. The data suggest that influenza virus M2 protein possesses a binding site for polyamines, distinct from the amantadine binding site, which is normally masked by Na+ and which could be targeted by selective antiviral inhibitors.

Concentration and size distribution of airborne hexavalent chromium in electroplating factories

Studies have shown that chromium from electroplating factories can cause respiratory problems to workers after prolonged exposure. Since Taiwan has a relatively high number of electroplating factories and minimal data regarding chromium's effect on workers, the authors undertook this study focusing on the size distribution of airborne hexavalent chromium and its concentration levels within the factory. Both area and personal sampling were conducted using a particle fractionating sampler. Samples were analyzed using visible spectrophotometry. A comparison of three types of factories-chromium, nickel-chromium, and zinc-showed that the highest concentrations were found in chromium electroplating factories near the electroplating tank. Hexavalent chromium particles obtained from area sampling had mass median diameters between 1.67-6.38 microns and 0.75-4.73 microns for personal sampling. Particles of this high concentration and small size can enter and cause considerable damage to the respiratory tract.

Determination of carbohydrates by high-performance capillary electrophoresis with indirect absorbance detection

High-performance capillary electrophoresis (HPCE) methods with indirect absorbance detection (IAD) have been developed for the determination of carbohydrates, e.g. glucose, fructose, rhamnose, ribose, maltose, lactose, sucrose and gluconic acid. The suitability and performance of six background electrolytes (BGEs), i.e., 1-naphthylacetic acid (NAA), 2-naphthalenesulfonic acid, 1,3-dihydroxynaphthalene, phenylacetic acid, p-cresol and sorbic acid, for the IAD method were investigated. The effects of the concentration of the BGE, pH and temperature on the CE separation of these analytes were evaluated. NAA was found to be best suited as the carrier buffer and background absorbance provider for the detection at 222 nm. The optimal CE performance was found when employing 2 mM NAA, pH 12.2, at 25 degrees C. In comparison with the previous method that used sorbate as the BGE, the present method utilizing NAA shows a 3-6 fold increase in the separation efficiency and a 2-5 fold improvement in the detection limit. The calculated number of theoretical plates is in the range of 1.0-3.0 x 10(5). The precision of the present method for most sugar analytes, measured by the coefficient of variation (C.V.), typically, is less than 1% for the migration time and better than 3% for the peak height and peak area (n = 6). The detection limit is about 0.1 mM for all analytes, except for ribose for which it is about 0.2 mM. This new method is fast, accurate and can be readily applied to real biological samples for quantitative determination of selected carbohydrates.

Capillary electrophoretic analysis of cyclodextrins and determination of formation constants for inclusion complexes

Capillary zone electrophoresis (CZE) methods with indirect absorbance detection for analyzing mixtures of alpha-, beta-, and gamma-cyclodextrins (CDs) and their derivatives have been developed. Benzylamine, salicylic, sorbic, or 1-naphthylacetic acid (NAA) was utilized as background electrolyte (BGE) and absorbance provider. Separation of alpha-, beta-, and gamma-CD could be achieved in less than 18 min when the CZE was run in 2 mM NAA or 5 mM sorbate solution (pH 12.2) and detected by indirect absorbance at 222 or 254 nm, respectively. Mixtures of alpha- and beta-CDs, and dimethyl- and trimethyl-derivatives of beta-CD could also be analyzed by CZE, using 50 mM salicylic acid or benzylamine solution (pH 6.0) as BGE with indirect absorbance detection at 230 and 210 nm, respectively. CZE methods for determining the inclusion complex formation constants of various CDs for salicylic acid or benzylamine with either direct or indirect absorbance detection have also been developed. The formation constants of salicylate are in the range from ca. 8 +/- 0.3 mole-1 for the complex with alpha-CD to ca. 99 +/- 2 molarity-1 for the complex with methyl-beta-CD. The detection limits (determined at a signal-to-noise ratio of 3) for the NAA and the salicylate system are ca. 0.1 mM and 1 mM, respectively.

Analysis of the iron-sulfur clusters within the complex I (NADH:ubiquinone oxidoreductase) isolated from potato tuber mitochondria

The mitochondrial complex I (NADH:ubiquinone oxidoreductase) isolated from potato (Solanum tuberosum) has been investigated for the presence of iron-sulfur clusters. EPR spectroscopic analysis detected signals arising from clusters N1, N2, N3 and N4. Quantitation of the content of iron and sulfur within the isolated complex I showed the preparation to contain 22.6 mol acid-labile sulfide and 30.4 mol iron/mol complex I. The iron-sulfur cluster composition of the plant complex I appears to be similar to the well-known composition found in Neurospora crassa.

Evaluation of urinary pseudouridine as a tumor marker in lung cancer

The urinary concentration of pseudouridine, primarily a breakdown product of tRNA, was determined by high-performance liquid chromatography in 33 patients with small cell lung cancer (SCLC), 18 patients with non-small cell lung cancer (NSCLC), 18 patients with benign pulmonary diseases (eg, TB, COPD), and 16 healthy controls. The mean urinary pseudouridine concentration levels of the patients with SCLC, NSCLC, benign pulmonary disease and the healthy controls were 22.7 +/- 11.8, 15.6 +/- 6.0, 13.4 +/- 3.6, 12.1 +/- 3.2 nmol/mumol creatinine (mean +/- SD), respectively. The mean urinary pseudouridine concentration was significantly higher in patients with SCLC than that in patients with NSCLC, benign pulmonary disease and in the healthy controls. There was no significant difference in the urinary pseudouridine levels of patients with NSCLC and healthy controls or patients with benign pulmonary disease. Urinary pseudouridine levels above 18.5 nmol/mumol creatinine (mean value +/- 2SD for healthy controls) were noted in 54.5% of patients with SCLC, including 11 of 17 (64.7%) in extensive stage and seven of 16 (43.8%) in limited stage, and 27.8% of the patients with NSCLC. Of the 12 patients with SCLC who had follow-up urinary samples taken in series during chemotherapy courses, there was considerable urinary pseudouridine level change which paralleled the change in clinical response. Although urinary pseudouridine is not a specific marker for SCLC, it represents the tumor burden and reflects the clinical status. These findings indicate that urinary pseudouridine may be a useful tumor marker in patients with SCLC.

Fluorescent probes for cancer detection

Several new fluorescent dyes, derivatives of pyrene and of coumarin, were synthesized that have excitation and emission wavelength maxima considerably red-shifted as compared to most pyrene and coumarin compounds. These new fluorescent compounds have high extinction coefficients and high quantum yields, and they also are very environmentally sensitive, which makes them good probes of biological systems. Several of these fluorescent compounds are preferentially taken up and retained by leukemic and other cancer tissue cell lines as compared to normals, particularly 1,3-dihydroxy 6,8-pyrenedisodiumsulfonate and 3-(carboxymethylester)-7-julolidinocoumarin. These compounds may have some usefulness in cancer detection.

Calcium regulates troponin-tropomyosin binding in the reconstituted thin filament

Steady-state fluorescence anisotropy technique was used to determine the binding constant of troponin for IAEDANS-labeled tropomyosin under various conditions. In the absence of actin, Ca does not affect the binding between troponin and tropomyosin. The presence of actin greatly strengthens troponin-tropomyosin binding in the absence of Ca. However, Ca weakens troponin-tropomyosin binding by about 2.5-fold in the reconstituted filament. It is suggested that the Ca-regulated binding may serve as a molecular switch for the troponin molecule to get "on" and "off" the actin-myosin interaction site regulating muscle contraction-relaxation cycles.

Studies on the spatial arrangement of muscle thin filament proteins using fluorescence energy transfer

The distance between a pair of fluorophores attached to Cys-36 of beta-tropomyosin and Cys-373 of actin in reconstituted muscle thin filaments was measured by fluorescence energy transfer. Two pairs of donor/acceptor fluorophores, N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulfonic acid/5-iodoacetamidofluorescein and N-(1-pyrene)maleimide/dimethylamino-4-maleimidostilbene, were covalently attached to tropomyosin and actin. The energy transfer efficiencies in various reconstituted systems were determined from decrease in donor lifetime using nanosecond pulse fluorimetry. Based on the 8 to 13% energy transfer efficiency observed for the first donor/acceptor pair labeled on tropomyosin and actin, respectively, and a calculated critical distance of 45 A (assumed kappa 2 = 2/3) the distance between Cys-373 of actin and Cys-36 of beta-tropomyosin was estimated to be 65 A. Fluorescence energy transfer experiments using other donor/acceptor pairs gave similar results. Since Cys-373 of actin is thought to be in the myosin head-binding sites, the minimal distance between tropomyosin and the myosin-binding site on actin is estimated to be about 34.5 A. These results place some constraints on possible spatial arrangements of thin filament proteins.

Excimer fluorescence of pyrene-tropomyosin adducts

Studies of the fluorescence of N-(1-pyrene)maleimide and N-(1-pyrenyl)iodoacetamide adducts of rabbit skeletal muscle tropomyosin revealed the presence of excimer fluorescence characterized by a broad emission band at 480 nm with a shoulder at 505 nm. Monomer fluorescence decay exhibited different lifetimes, viz., about 3, 22 and 87 ns for the pyrenemaleimide adduct; about 2.5, 11 and 51 ns for the aminolyzed maleimide adduct; and 2.5, 15 and 74 ns for the pyrenyliodoacetamide adduct. Almost identical excimer fluorescence lifetimes were found for all adducts; about 9, 35, and 65 ns. Excimer fluorescence was sensitive to changes in ionic strength and pH of the medium while monomer fluorescence did not change. The protein denaturants guanidine hydrochloride and urea caused dissociation of the two tropomyosin subunits and partial disappearance of excimer fluorescence, but not as effectively as the hydrophobic surfactant sodium dodecyl sulfate. The sensitivity of excimer fluorescence to changes in the microenvironment make these pyrene derivatives very useful probes for studying conformational changes and binding interaction of tropomyosin with other contractile proteins. The unique location of the excimer probe at tropomyosin Cys-190 and its characteristic long lifetimes could make it useful in time-resolved anisotropy studies and fluorescence energy-transfer experiments.

Fluorescence spectroscopic studies of pyrene-actin adducts

Reaction kinetic studies of the sulfhydryl-directed fluorescent probes N-(1-pyrene)maleimide (PM) and N-(1-pyrenyl)iodoacetamide with actin from rabbit skeletal muscle showed that there were three accessible sulfhydryl groups in actin. Fluorescence spectral studies showed energy transfer from aromatic amino acid residues to fluorophore reacted at Cys-373, as well as weak excimer fluorescence probably due to doubly labeled molecules at Cys-10 and Cys-373. These results provide further evidence that trytophan and tyrosine residues are located near the probe attached to Cys-373 or Cys-10 and the latter two thiols are in close proximity. In age PM-labeled F-actin, the succinimido ring of PM underwent intramolecular aminolysis, resulting in large emission spectral changes and increased excimer fluorescence. Solvent perturbation studies indicate that the probes were located in a hydrophobic environment; their quantum yield and spectrum properties were very sensitive to changes in the microenvironment. Nanosecond-pulse fluorimetry studies revealed complex fluorescence emission decays with three intrinsic lifetimes in adducts with low molecular weight thiols as well as in labeled proteins. Fluorescence lifetimes were 17, 48 and 111 ns for the pyrenemaleimide adduct of actin, and 3, 14 and 60 ns for the pyrenyliodoacetamide adduct. Supporting evidence is given for the argument that multiple fluorescence lifetimes are an intrinsic property of the pyrene derivatives and are not due to the presence of impurity or heterogeneity in the protein reaction sites. Because of their high sensitivity and long lifetimes, pyrene derivatives are extremely useful.

Circular-dichroic studies on the conformational behaviour of troponin and tropomyosin from bovine cardiac muscle

Bovine cardiac troponin is similar to rabbit skeletal troponin with respect to secondary structure, amino acid composition and molecular weight of the subunits, but differs slightly with respect to biological activity and surface charges of the subunits. Previous circular-dichroic studies of the subunits and recombination of subunits have indicated significant Ca2+-induced delocalized conformational changes. Present studies of the native troponin complex are not in accord with such changes. Furthermore the formation of the troponin-tropomyosin complex in vitro results in no delocalized conformational changes, nor does it sensitize troponin to Ca2+-induced changes. It is suggested that the troponin complex cannot be dissociated into subunits without significant and irreversible conformational perturbation.

Does myosin-substrate interaction in vitro result in a delocalized conformation change?

The effect of substrate on the far UV (185-250 nm) and near UV (250-325 nm) circular dichroism (CD) of myosin and heavy meromyosin (HMM) was studied. The following results were obtained with the addition of ATP (during various conditions of hydrolysis), ADP, and pyrophosphate: (1) no changes were observed in the far UV CD, (2) ATP and ADP perturbed the near UV CD only at spectral regions below 280 nm coinciding with the regions of their optical activity, (3) the optically inactive pyrophosphate caused no change in the near UV CD, and (4) myosin and HMM gave exactly the same results. These results suggest that myosin-substrate interaction in vitro does not result in a delocalized conformational change.