Epidermal growth factor receptor overexpression in resected pancreatic cancer

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Background: The effect of overexpression of epidermal growth factor receptor (EGFR) in pancreatic carcinoma is uncertain. In this study, we examine the association between EGFR overexpression (membrane and cytoplasmic) and histopathologic features and clinical outcomes in patients post resection.

Methods: Seventy three patients underwent curative resection for pancreatic cancer from 4/08 to 4/10. Tumor EGFR expression was determined immunohistochemically using EGFR pharmDxTM kit. Cytoplasmic overexpression was considered positive if EGFR expression was seen in the cytoplasm in ≥10% of cells. Cell membrane staining scores were assigned: 0 (no membrane staining), 1+ (incomplete membrane staining in ≥ 10% of cells, 2+ (complete weak/moderate membrane staining in ≥ 10% of cells) and 3+ (complete heavy staining in ≥ 10% of cells). A score of 2+ and 3+ were considered as membrane overexpression. Comparisons between EGFR overexpression and clinicopathologic features were assessed by chi-square test with p-value < 0.05 as statistically significant. Proportional hazard regression was used to estimate progression free survival and overall survival.

Results: Out of 73 patients, 43 (59%) and 50 (68%) patients had membrane and cytoplasmic EGFR overexpression respectively. AJCC stages were: stage I: 8, stage II: 63, stage III: 1 and stage IV: 1 patient. There was statistically significant correlation between cell membrane EGFR overexpression and lymph node positivity (p=0.04). Membrane EGFR overexpression was not significantly associated with local invasion, margin positivity, vascular invasion, perineural invasion, histologic grade or stage. Cytoplasmic EFGR overexpression was significantly associated with margin positivity (p=0.01) only. The hazard ratios (95% CI) for PFS and OS in patients with membrane EGFR overexpression was 1.37 (0.72-2.60) and 1.27 (0.62-2.61) respectively. The corresponding values for patients with cytoplasmic overexpression were 1.65 (0.80-3.37) and 1.25 (0.58-2.71) respectively.

Conclusions: Membrane EGFR overexpression was associated with lymph node status and cytoplasmic EFGR overexpression with margin positivity. There was no association of EFGR expression and clinical outcomes.

No significant financial relationships to disclose.

Patients' experiences of a diagnosis of Hughes' syndrome

The objectives of the study were to describe the experience of patients immediately prior to a diagnosis of Hughes syndrome (HS) or antiphospholipid syndrome and post-diagnosis. A questionnaire survey was carried out set in the Hughes Syndrome Foundation, St. Thomas' Hospital, London, 2006. Participants were all patients who are members of the Hughes Syndrome Foundation. The main outcome measures were responses to a questionnaire relating to the experiences of people with a diagnosis of HS, such as number of hospitalisations, number of consultants seen, number of miscarriages, etc. A total of 157 patients completed the questionnaire, giving a response rate of 60.4%. Most (85%) were women and mean age was 46 years (SD 12). The median time to diagnosis was 3 years. The median number of consultants seen was 2 (max 19) with a median time in hospital pre-diagnosis of 10 days. The most common initial diagnoses were migraines, multiple sclerosis and systemic lupus erythematosus. Among women, 46% had had a miscarriage. Two thirds of respondents thought a blood test would have led to an earlier diagnosis. Comments from patients indicated a lack of awareness among specialists and general practitioners. The survey demonstrated a long time lag for diagnosis of Hughes syndrome, with increased costs to the NHS and emotional and financial cost to the patient. Greater awareness of this condition would benefit patients and the NHS.

Microarray analysis and organization of circadian gene expression in Drosophila

We have used high-density oligonucleotide arrays to study global circadian gene expression in Drosophila melanogaster. Coupled with an analysis of clock mutant (Clk) flies, a cell line designed to identify direct targets of the CLOCK (CLK) transcription factor and differential display, we uncovered several striking features of circadian gene networks. These include the identification of 134 cycling genes, which contribute to a wide range of diverse processes. Many of these clock or clock-regulated genes are located in gene clusters, which appear subject to transcriptional coregulation. All oscillating gene expression is under clk control, indicating that Drosophila has no clk-independent circadian systems. An even larger number of genes is affected in Clk flies, suggesting that clk affects other genetic networks. As we identified a small number of direct target genes, the data suggest that most of the circadian gene network is indirectly regulated by clk.

Consequence of beta 16 and beta 112 replacements on the kinetics of hemoglobin assembly

The rates of alpha/beta monomer combination of four beta(A) variants (beta 112C --> S, beta 112C --> D, beta 112C --> T, and beta 112C --> V) in the presence and absence of beta 16G --> D (beta(J)) were measured in an attempt to assess the consequences of amino acid substitution at both a surface (beta 16) and an alpha(1)beta(1) interface (beta 112) residue on oxyhemoglobin assembly. Rates of alpha/beta monomer combination determined spectrally in 0.1 M Tris-HCl, 0.1 M NaCl, 1 mM EDTA, pH 7.4, at 21.5 degrees C differed by over 40-fold (22 +/- 2.0 to 0.49 +/- 0.1 x 10(5) M(-1) s(-1)), and were in the order: HbA beta 112S = HbJ beta 16D, beta 112S > HbA beta 112D = HbJ beta 16D, beta 112D > HbA > Hb J > HbA beta 112T = HbJ beta 16D, beta 112T > HbJ beta 16D, beta 112V > HbA beta 112V. This extensive kinetic investigation of single/double amino acid-substituted recombinant hemoglobin molecules, in conjunction with molecular modeling studies, has allowed examination of an array of unique alpha/beta subunit interactions and assembly processes.

Carboxyl-terminal modification alters the subunit interactions and assembly pathways of normal and sickle hemoglobins

Parallel isofocusing studies established that carboxypeptidase A removal of the His-146 (HC3) and Tyr-145 (HC2) residues of beta heme subunits affected the assembly properties of both Des beta(A) and Des beta(S) with alpha heme chains, albeit to differing degrees. Indeed, the rate of Des beta(A) oligomer dissociation (k1), as determined by visible spectroscopy, was 4.3-fold faster than that of its native beta(A) counterpart. Furthermore, Soret spectral studies have affirmed distinct rates of normal (HbA), sickle (HbS), and Des HbA hemoglobin assembly (k'2) from their alpha and beta [Des beta(A)] heme-containing monomers. Matching kinetic analysis of Des beta(A) and Des beta(S) chain assembly (with an identical a chain) revealed 4.6- and 7.8-fold faster combination rates than those seen for beta(A) and beta(S) chains, respectively. This 3-fold disparity in rates strongly supports the critical role of the beta-6 (A3) residue, and its amino-terminal region, in a chain partner recognition and subsequent human hemoglobin assembly.

Wild-type circadian rhythmicity is dependent on closely spaced E boxes in the Drosophila timeless promoter

Transcriptional regulation plays an important role in Drosophila melanogaster circadian rhythms. The period promoter has been well studied, but the timeless promoter has not been analyzed in detail. Mutagenesis of the canonical E box in the timeless promoter reduces but does not eliminate timeless mRNA cycling or locomotor activity rhythms. This is because there are at least two other cis-acting elements close to the canonical E box, which can also be transactivated by the circadian transcription factor dCLOCK. These E-box-like sequences cooperate with the canonical E-box element to promote high-amplitude transcription, which is necessary for wild-type rhythmicity.

Incidence and predictors of myocardial infarction among patients with atrial fibrillation

OBJECTIVES

We sought to evaluate the utility of excluding myocardial infarction (MI) in patients presenting to the emergency department (ED) with atrial fibrillation (AF) and to identify predictors of MI in this group.

BACKGROUND

Patients with AF are frequently admitted to the hospital, in part, to exclude an associated MI. There are no prospective data on unselected patients to support this common practice.

METHODS

We conducted a prospective cohort study of all patients who presented to a single-center ED with the primary diagnosis of AF.

RESULTS

Of a total of 255 patients, 190 (75%) were admitted to the hospital, and 109 of them underwent a standard "rule-out MI" protocol. Of these 109 patients, six (5.5%) were identified as having an acute MI at the time of admission. Chest pain was present in 39% of patients, with a sensitivity and specificity for the occurrence of MI of 100% and 65%, respectively. ST segment elevation or depression was present in 43% of patients, with a sensitivity and specificity of 100% and 51%. The presence of either major ST segment depression (>2 mm) or elevation on the admission electrocardiogram (ECG) was present in 6%, with a sensitivity of 100% and a specificity of 99%. The resulting positive and negative predictive values were 86% (95% confidence interval [CI] 42% to 99%) and 100% (95% CI 96% to 100%), respectively. Use of this criterion would have reduced the number of rule-out MIs in our study group by 94%, with no loss of sensitivity.

CONCLUSIONS

Chest pain and ST segment depression are extremely common findings in patients presenting to the ED with AF and have limited power to predict MI. In contrast, ECG evidence of ST segment elevation or depression >2 mm appears to be a reliable discriminator of which patients are at risk for MI. Patients without significant ST segment changes are at very low risk for MI and may not require performance of the rule-out MI protocol or hospital admission if clinically stable.

Wavelength-dependent spectral changes accompany CN-hemin binding to human apohemoglobin

The interaction of apohemoglobin with two heme derivatives, CN-protohemin and CN-deutero-hemin, was monitored at multiple Soret wavelengths (417-423 and 406-412 nm, respectively) in 0.05 M potassium phosphate buffer, pH 7.0, at 10 degrees C and revealed, as previously reported, a multiphasic kinetic reaction. Wavelength-dependent reactions were observed for both CN-protohemin and CN-deuterohemin derivatives with the alpha chain (bathochromic entity) displaying faster (4- to 7-fold) rates throughout the courses of both heme-binding reactions. The basis of this spectrally heterogeneous kinetic phenomenon could be deduced from molecular modeling studies of alpha- and beta-chain structures. Key differences in the number of stabilizing contacts of the two chains with the peripheral alpha propionyl 45(CE3); 58(E7); 61(E10) as well as the beta vinyl 38(C4); 71(E15); 106(G8) groups were found. Furthermore, RMS plots comparing apo- and heme-containing subunits reveal substantial structural disparities in the C-CD-F-FG helical regions of the alphabeta dimer interface.

takeout, a novel Drosophila gene under circadian clock transcriptional regulation

We report the identification and characterization of a new Drosophila clock-regulated gene, takeout (to). to is a member of a novel gene family and is implicated in circadian control of feeding behavior. Its gene expression is down-regulated in all of the clock mutants tested. In wild-type flies, to mRNA exhibits daily cycling expression but with a novel phase, delayed relative to those of the better-characterized clock mRNAs, period and timeless. The E-box-containing sequence in the to promoter shows impressive similarities with those of period and timeless. However, our results suggest that the E box is not involved in the amplitude and phase of the transcriptional cycling of to. The circadian delayed transcriptional phase is therefore most likely the result of indirect regulation through unknown transcription factors.

Surface and interface beta-chain residues synergistically affect hemoglobin assembly

Homo- and heterotetramer formations of beta112 variants (beta(112Cys-->Asp), beta(112Cys-->Ser), beta(112Cys-->Thr), and beta(112Cys-->Val)) of hemoglobin were characterized in the presence and absence of beta(16Gly-->Asp) in vitro. In all cases an alteration in overall surface charge (beta(16Gly-->Asp)) decreased the beta(4) homotetramer stability (association constants as determined by gel-permeation chromatography) albeit to differing extents. In contrast, competition experiments of hemoglobin subunits showed that heterotetramer formation was promoted by this substitution. Order of increase in tetramer formation by the additional negative surface charge in the beta112 variants was as follows: Hb betaG16D, C112D > Hb betaG16D, C112S > Hb betaG16D > Hb G16D, C112T > Hb betaG16D, C112V. Thus, the overall surface charge of the beta chain and its contribution to electrostatic interaction in these instances appear to act in synergy with alpha(1)beta(1) interface residues to affect the assembly of hemoglobin molecules.

Soret spectroscopic and molecular graphic analysis of human semi-beta-hemoglobin formation

The interaction of heme-free alpha (alpha(o)) and heme-containing beta (beta(h)) chains of human hemoglobin has been monitored in 0.1 M potassium phosphate buffer, pH 7 or 8, at 5 degrees C. Soret zero and first-derivative spectra were consistent with a uniform association reaction. Stopped-flow investigations demonstrated association rates on the order of 10(7) M(-1) s(-1). This was 100-fold more rapid than the reported rate of combination of alpha(h) and beta(h) proteins. This encounter-like rate of semi-beta-hemoglobin (alpha(o)beta(h)) formation was increased by raising the pH from 7 to 8. pH change is known to affect the spatial arrangement of AB-GH helical entities. Molecular graphic analysis of modeled alpha(o) protein superimposed over native alpha(h) protein revealed an apo Mb-like structure with well-defined AB-GH segments. Repositioning of these core helical segments, resulting in increased conformational freedom of the alpha1beta1 interface, was apparently responsible for the enhanced association properties of the alpha(o) protein.

Analysis of the global architecture of hemoglobin A2 by heme binding studies and molecular modeling

The kinetics of CNProto- and CNDeutero-hemin binding to apohemoglobin A2 was investigated in a stopped-flow device in 0.05 M potassium phosphate buffer, pH 7, at 10 degrees C. The overall kinetic profile exhibited multiple phases: Phases I-IV corresponding with heme insertion (8.5-13 x 10(7) M(-1) s(-1)), local structural rearrangement (0.21-0.23 s(-1)), global alphadelta structural event (0.071-0.098 s(-1)), and formation of the Fe-His bond (0.009-0.012 s(-1)), respectively. Kinetic differences observed between apohemoglobin A2 and apohemoglobin A (previously studied) prompted an analysis of the structures of beta and delta chains through molecular modeling. This revealed a structural repositioning of the residues not only at, but also distant from the site of the amino acid substitutions, specifically those involved in the heme contact and subunit interface. A significant global change was observed in the structure of the exon-coded 3 region and provided additional evidence for the designation of this as the subunit assembly domain.

Fluorescence studies of human semi-beta-hemoglobin assembly

The intrinsic fluorescence properties of human alpha apohemoglobin at protein concentrations from 1 to 5 microM in 0.1 M potassium phosphate buffer, pH 7 or 8 at 5 degrees C were monitored in the absence and presence of a fixed concentration (5 microM) of a fluorescence quenching heme-containing native or Des (146-His, 145-Tyr) beta chain partner. These "reverse quenching" studies revealed that the emission intensity changes observed correlated well with protein concentration and theoretical extent of semi-beta-hemoglobin assembly. Furthermore, the relative quenching efficiencies were calculated to be 0.32, 0.25 and 0.61 for beta (pH 7), beta (pH 8) and Des beta (pH 7) chains, respectively. Thus, heme-mediated quenching was sensitive to the expected pH induced alpha apohemoglobin conformational change and to alteration in beta chain structure. Intramolecular changes induced by carboxylterminal modification (decreased "beta chain self-quenching") appeared to enhance the intermolecular rearrangements (increased "alpha chain partner quenching") seen upon subunit assembly.

Spectral demonstration of semihemoglobin formation during CN-hemin incorporation into human apohemoglobins

The incorporation of CN-hemin into three human adult apohemoglobin species (apohemoglobin, alpha-apohemoglobin, and apohemoglobin modified at its beta93 sulfhydryl with p-hydroxymercuribenzoate) has been monitored at micromolar concentrations in 0.05 M potassium phosphate buffer, pH 7.0, at 10 degrees C. In all cases, Soret spectral blue shifts accompanied CN-protohemoglobin but not CN-deuterohemoglobin formation. This finding in conjunction with isofocusing studies provided evidence of a CN-protosemi-alpha-hemoglobin intermediate, the formation of which appeared to be a direct consequence of CN-protohemin-alpha heme pocket interactions. The kinetics of full reconstitution of CN-protohemoglobin and CN-deuterohemoglobin revealed four distinct phases that apparently correlated with heme insertion (Phase I), local structural rearrangement (Phase II), global conformational response (Phase III), and irreversible histidine iron bond formation (Phase IV). These phases exhibited rates of 7.8-22 x 10(7) M(-1) s(-1), 0.19-0.23 s(-1), 0.085-0.12 s(-1), and 0.008-0.012 s(-1), respectively. Partial (50%) reconstitution with CN-protohemin, in contrast, revealed only three kinetic phases (with Phase III missing) of heme incorporation into native and p-hydroxymercuribenzoate-modified apohemoglobin. Furthermore, the absence of Phase III slowed the rate of proximal bond formation. These findings support the premise that irreversible assembly of CN-protosemi-alpha-hemoglobin is deterred by the presence of a heme-free beta partner, the consequence of which may be that intermolecular heme transfer is encouraged under conditions of heme deficiency in vivo.

Carboxyl-terminal modification influences subunit assembly of sickle hemoglobin beta chains

The subunit assembly properties of isolated beta and Des(His-146,Tyr-145) beta chains of sickle hemoglobin were investigated by isoelectric focusing over a protein concentration range from 500-125 microM in heme. Two components (presumably tetramer and monomer) and three components (designated tetramer, dimer and monomer) were visualized for beta s and Des(His-146,Tyr-145) beta s chains, respectively. Intensitometric quantitation of Des(His-146,Tyr-145) beta s chains demonstrated a similar distribution of all three structural components before and after the addition of their heteropartner alpha chains. This is in direct contrast to the reported preferential loss of Des(His-146,Tyr-145) beta A monomer species upon assembly and points to a major role of the beta 6 residue in the overall structural homeostasis of carboxylterminal modified human beta chains.

Effect of carboxyterminal modification on the oligomeric structure of human beta hemoglobin

A broad beta chain band region containing multiple components was observed with both native beta and Des(His-146, Tyr-145) beta chains following isoelectric focusing on agarose gels (pH 6.0-8.0). In contrast to the tetramer-monomer system of beta chains, a distinct separation of three components (tetramer, dimer and monomer) was seen for Des(His-146, Tyr-145) beta chains indicative of an oligomeric structural beta model with a stable dimer species. Protein dilution (500 to 15.6 microM in heme) amplified the more cathodic (presumably dimeric and monomeric) components of these chains, and titration with partner alpha chains resulted in a selective depletion of the monomer (most cathodic) component which could be quantitatively correlated with assembly of the hemoglobin tetramer.

Fluorescence studies of normal and sickle beta apohemoglobin self-association

The acrylamide quenching of the intrinsic tryptophanyl fluorescence of normal and sickle beta apohemoglobins has been studied in 0.05 M potassium phosphate buffer, pH 7.5, at 5 degrees C over a protein concentration range from 1 to 50 microM. Analysis of quenching dynamics revealed a strong dependence on acrylamide concentration for the intrinsic fluorescence of both normal and sickle beta apohemoglobins, suggesting that one tryptophanyl residue [presumably that at position 37(C3)], was more accessible to collisional quencher than the other beta tryptophanyl residue [15(A12)]. Additional studies, which altered viscosity and subunit assembly experimental parameters, supported the assignment of residue 37 as the more dynamically accessible residue. Finally, the quenching data were also found to be dependent on protein concentration, implying that this difference in the mobility between the two residues is a sensitive probe of self-aggregation. Extrapolated dynamic quenching constants at low concentration of acrylamide were used to estimate the dimer-monomer equilibrium dissociation constants of normal and sickle beta apohemoglobins, and were found to be 5.6 and 2.4 microM, respectively, thus demonstrating distinct self-association properties of beta A and beta S apohemoglobins.

Monitoring the effect of subunit assembly on the structural flexibility of human alpha apohemoglobin by steady-state fluorescence

A single energy transfer distance, between the sole intrinsic tryptophanyl donor [14(A12)] and a nonfluorescent sulfhydryl acceptor probe (4-phenylazophenylmaleimide, PAPM) attached to the only cysteine [104(G11)], has been employed to examine the effect of subunit assembly on the structure of the heme-free human alpha-hemoglobin. Efficiencies of energy transfer were measured in 0.05 M potassium phosphate buffer, pH 7.0, at 5 degrees C, and the structural flexibility of alpha-apohemoglobin, in the absence and presence of human beta-heme-containing chains, was examined by a steady-state solute quenching technique. The quenched efficiencies (EQ) and Förster distances (R0Q) were analyzed by least-squares to determine the goodness of fit (chi R2) for the assumed distribution parameters: average distance r and half-width hw. Data for alpha-apohemoglobin in the absence and presence of beta h chains yielded values for r of 18 and 22 A and hw of 20 and 8.5 A, respectively. Although the increase in r for alpha-apohemoglobin in the presence of beta h chains was presumably a consequence of additional quenching from the heme moiety, the change in the half-width strongly indicated a decrease in the flexibility of the alpha-apohemoglobin chain within the assembled protein. A transition in structural flexibility similar to that demonstrated here may be an important aspect of human hemoglobin assembly.

Steady state fluorescence energy transfer measurements of human alpha apohemoglobin structure

A nonfluorescent reagent, 4-phenylazophenylmaleimide [4-PAPM], was attached to the sole cysteine residue [104(G11)] of alpha apohemoglobin (alpha degree) and served as an energy acceptor for the single intrinsic tryptophanyl [14(A12)] donor. This novel fluorescence system provided a transmolecular vehicle by which the overall structure of alpha degree could be monitored in 0.05 M potassium phosphate buffer at 5(0) C. Ratio of the emission intensities at 335 nm for monomeric solutions (5 x 10(-6) M) of both alpha degree and alpha degree [4-PAPM] furnished a measure of the efficiency of energy transfer and average distance of separation (r). An apparent increase in the value of r was observed from pH 6.5 to 8.5, suggesting that the conformation (the structural relationship of the A and G helical segments) of alpha degree is responsive to its electrostatic environment.

Kinetics of human apohemoglobin dimer dissociation

Heme chain exchange was employed to investigate the dimer dissociation reaction of human apohemoglobin in 0.1 M potassium phosphate buffer, pH 7.0, at 20 degrees C. Incubation of apohemoglobin (alpha 0 beta 0) with either alpha h (or beta h) allowed the monitoring of the formation of a semihemoglobin alpha h beta 0 (or alpha 0 beta h) species with time. Analysis revealed that the rate of formation of both semihemoglobins was essentially identical and coincided with the disappearance of heme chain. Time courses were exponential and followed first order kinetics yielding a dimer dissociation rate constant of 0.54 (+/- 0.07) h-1. A study over the pH range from 6.5 to 8.0 revealed that this dissociation rate exhibited a maximum at pH 7.0 (implicating a histidyl residue). The effect of temperature (6-37 degrees C) on this dimer dissociation rate yielded a linear Arrhenius Plot and an energy of activation of 7.2 kcal/mol. These results are consistent with alpha G-beta G helical pairing being a major contributor to apohemoglobin dimer integrity.

Role of alpha and beta carboxyl-terminal residues in the kinetics of human oxyhemoglobin dimer assembly

Human oxyhemoglobin assembly was evaluated in the Soret region by rapidly mixing normal and carboxypeptidase-digested chains (1-10 x 10(-6) M, heme basis) in 0.1 M Tris-HCl, 0.1 M NaCl, 1 mM EDTA, pH 7.4, at 21.5 degrees C. Rate constants of 1.14 (+/- 0.09) and 2.11 (+/- 0.06) x 10(5) M-1 S-1 were measured for the association of Des(Arg-141) alpha with beta A and alpha A with beta A chains, respectively. The slower combination rate of Des(Arg-141) alpha with beta A chains is in agreement with that predicted solely on the basis of electrostatic considerations, as are the measured rate constants of 0.75 (+/- 0.12) and 1.86 (+/- 0.08) x 10(5) M-1 S-1 obtained for the combination of Des(Arg-141) alpha with variant beta S (Glu-6-->Val) and beta N Baltimore (Lys-95-->Glu) chains, respectively. However, the combination rates of alpha A and Des(Arg-141) alpha with beta A chains measured in the pH range from 7.0 to 9.0 demonstrated that the altered overall surface charge was not the only determinant of the assembly rates observed for Des(Arg-141) alpha chains. Furthermore, a rate constant of 11.3 (+/- 0.05) x 10(5) M-1 S-1 (which is 5.4-fold faster than the rate of alpha A beta A dimer assembly) was observed for Des(His-146,Tyr-145) beta chains. These kinetic studies suggest a critical role for the carboxyl-terminal domain in the assembly of human hemoglobin in vitro and perhaps in vivo.

Hb Rancho Mirage [beta 143(H21)His----Asp]; a variant in the 2,3-DPG binding site showing normal oxygen affinity at physiological pH

Hb Rancho Mirage was detected in a 17-year-old male in association with a mild anemia. Hemoglobin electrophoresis revealed the variant had a mobility between Hbs A and J on cellulose acetate (pH 8.6) and a mobility like Hb F on citrate agar (pH 6.4). A substitution of His----Asp was found at position 143 in the beta chain, a residue that contributes to the anionic 2,3-DPG binding site in Hb. This variant exhibited normal oxygen affinity at physiologic pH and reduced affinity at alkaline pH. This suggested a subtle shift in the allosteric equilibrium due most likely to the introduction of a negative charge that stabilized the 2,3-DPG pocket. Both homotrophic (heme-heme) and heterotropic (2,3-DPG and protons) effects were reduced; this might be a consequence of an alteration in the carboxyl terminal region of the beta-subunits. Although a His----Asp substitution would be considered to cause reasonable disruption of the 2,3-DPG and C-terminal conformation of the beta- subunits, the properties of Hb Rancho Mirage suggest that, in fact, there appear to be no major perturbation of the critical C-terminal residues.

Safety and efficacy of a new regimen of intravenous recombinant tissue-type plasminogen activator potentially suitable for either prehospital or in-hospital administration

The safety and efficacy of a new regimen of intravenous recombinant tissue-type plasminogen activator (rt-PA) potentially suitable for either pre- or in-hospital administration were assessed in 60 patients with acute myocardial infarction in an open label coronary angiographic study. The regimen consisted of a 20-mg bolus dose followed 30 min later by a delayed infusion of 80 mg over 2 h. This regimen was designed to facilitate prehospital administration of rt-PA. Infarct-related artery patency (Thrombolysis in Myocardial Infarction [TIMI] grade 2 or 3 flow) was observed in 40 of 53 patients at 60 min (75.5%, 95% confidence intervals [CI] 61% to 84%) and in 55 of 60 patients at 90 min (91.7%, 95% CI 80% to 95%) after the rt-PA bolus. By 90 min the majority of patients (55%) exhibited TIMI grade 3 flow; infarct artery patency at 120 min was 84.9%. During hospitalization definite recurrent ischemia occurred in nine patients (15%); nonfatal recurrent infarction was noted in one (1.7%). Four patients (6.7%) experienced major bleeding, including one with intracranial bleeding. There were seven deaths (11.7%). Mortality was significantly influenced by the occurrence of cardiogenic shock, which was present in five patients at the time of enrollment. Blood fibrinogen levels were obtained before and during rt-PA infusion. At baseline and 30 and 150 min after the bolus dose, the mean fibrinogen level (+/- SD) was 284.83 +/- 77.39, 237.96 +/- 76.92 and 192.04 +/- 57.82 mg/dl, respectively. Compared with the baseline value, there was a significant (p less than 0.05) decrease in fibrinogen at both 30 and 150 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural, functional, and subunit assembly properties of hemoglobin Attleboro [alpha 138 (H21) Ser----Pro], a variant possessing a site maturation at a critical C-terminal residue

Hemoglobin Attleboro, a new alpha-chain variant with a substitution of proline for serine at position 138 (H21), was found to be a noncooperative high-affinity hemoglobin (P50 = 0.26 mmHg at pH 7 and 20 degrees C) which lacked an alkaline Bohr effect. Addition of 2,3-diphosphoglycerate (DPG) or inositol hexaphosphate (IHP) led to a decrease in oxygen affinity but to no alteration in either Bohr effect or cooperativity. Ligand binding kinetics studies revealed an overall rate of oxygen dissociation at pH 7.0 and 20 degrees C that was 2.7-fold slower than that for Hb A. At pH 8.5, the kinetic profile was identical with that at pH 7, confirming the absence of a Bohr effect for this variant hemoglobin. Measurement of the rate of oxygen dissociation with carbon monoxide replacement indicated a lack of cooperativity. Sedimentation velocity experiments yielded s20,w values of 2.8 and 4.3 for 65 microM solutions of oxyhemoglobins Attleboro and A, respectively (indicating an enhancement in the oxy dimer population of this variant). Studies of the carbon monoxide combination of this variant revealed an association rate 20-fold faster than that for Hb A; only in the presence of a 1000-fold molar excess of IHP was there a significant reduction in the overall rate. Rapid-scan and traditional stopped-flow experiments conducted in the Soret Soret region demonstrated an alteration in the structure and rate of assembly of the deoxy tetramer of Hb Attleboro relative to that of Hb A. The abnormal properties of this hemoglobin variant can be attributed to major perturbations in the C-terminal region.

Kinetics of heme binding to semi-alpha-hemoglobin

The binding of carbonmonoxyheme to semi-alpha-hemoglobin and to an apohemoglobin control was investigated using stopped-flow techniques in 0.025 M potassium phosphate buffer, pH 7 and 10 degrees C. The resultant second order kinetic data were analyzed by the classical model which assumes the existence of an intermediate complex which either redissociates to reactants or undergoes an irreversible conversion to form hemoglobin. The rate constants for the latter unimolecular process were apparently not experimentally different for semi-alpha-hemoglobin and apohemoglobin (360 ( +/- 100) s-1 and 480 ( +/- 60) s-1, respectively). However, the equilibrium dissociation constant for the intermediate of semi-alpha-hemoglobin (Kd = 9.3 ( +/- 2.6) micromolar) was approximately two fold greater than that of apohemoglobin (Kd = 4.1 ( +/- 0.5) micromolar). The reduced stability of the semi-alpha-hemoglobin complex was postulated to be due to the lower affinity of the beta pocket for heme. The studies reported here address the possible role of semi-alpha-hemoglobin as an intermediate in the assembly of hemoglobin in vivo.

An investigation of human oxyhemoglobin beta tetramer dissociation using haptoglobin binding

Haptoglobin was used as a macromolecular probe to investigate the formation of human oxyhemoglobin beta chain dimers from tetramers in 0.1 M potassium phosphate buffer, 20 degrees C at pH 7 and pH 8. Monitoring of spectral changes upon mixing haptoglobin with beta heme chains (2.5 and 5 micromolar) revealed an overall decrease in absorbance accompanied by a shift of the Soret spectral peak from 415 to 417 nm. The magnitude of the absorbance decrease was proportional to the beta concentration; the time courses consistently yielded greater color at pH 8 than at pH 7. At pH 8, two exponential phases of 0.47 min-1 and 0.084 min-1 were seen whose rates remained invariant with concentration. In contrast, only one exponential process was evident at pH 7, yielding a first order rate constant of 0.21 min-1. We have spectrophotometrically followed the beta chain tetramer to dimer dissociation reaction, thus providing information about the contribution of this step to hemoglobin assembly.

Status of equine viral arteritis in Kentucky, 1985

Clinical cases of equine arteritis virus infection have not been diagnosed in Kentucky since 1984, and there has been no indication that any of the horses involved in the 1984 epizootic have since been responsible for spread of the disease to horses in other states or other countries. Cases of abortion caused by naturally acquired infection with this virus have not been confirmed in 1984 or 1985. Neither field nor vaccine strains of equine arteritis virus have been shown to induce teratologic abnormalities or the carrier state in foals born to infected or vaccinated mares. The carrier stallion appears to have played a major epidemiologic role in the dissemination and perpetuation of the virus. A commercial modified live equine viral arteritis vaccine was found to be safe and efficacious for stallions and mares. The disease can be controlled by immunizing the stallion population and by restricting the breeding of equine arteritis virus-shedding stallions to vaccinated or seropositive mares, followed by an appropriate period of isolation from other nonvaccinated Equidae.

The kinetics of assembly of normal and variant human oxyhemoglobins

The kinetics of assembly have been monitored spectrophotometrically for normal and variant human oxyhemoglobins in 0.1 M Tris, 0.1 M NaCl, 1 mM Na2EDTA, pH 7.4, at 21.5 degrees C. Oxyhemoglobin versus oxy chain static difference spectra were performed and revealed subtle but significant absorption changes in both the visible and Soret regions. Kinetic experiments were performed by rapidly mixing equivalent (in heme) concentrations of alpha and beta A chains and following the change in absorbance at 583 nm with time. Over a protein concentration range of 10-100 microM in heme prior to mixing, these time courses were homogeneous and followed first-order kinetics, yielding a value of 0.069 s-1 for the apparent rate constant of dissociation of oxygenated beta A chain tetramers. Under these conditions, the overall assembly of oxyhemoglobins S (beta 6Glu----Val) and N-Baltimore (beta 95Lys----Glu) were also governed by the rates of dissociation of their respective oxygenated beta S and beta N-Baltimore chain tetramers with the apparent first-order rate constants of 0.044 and 0.15 s-1, respectively. In the Soret region, the alpha, beta monomer combination reaction could be observed if the protein concentration (heme basis) was lowered and if protein nonequivalency (beta chain exceeded alpha chain concentration) mixing experiments were performed. A kinetic oxyhemoglobin A, oxy-alpha, oxy-beta A monomer difference spectrum could be generated, and simple second-order kinetics were observed (415 nm) yielding rate constants of 2.3, 3.3, and 4.8 X 10(5) M-1 s-1 for the assembly of oxyhemoglobins S, A, and N-Baltimore, respectively. To our knowledge, this is the first kinetic study to reveal significant differences between the rate of association of alpha and beta monomers of hemoglobin A and those of two distinctly charged hemoglobin variants.

Electrostatic attraction governs the dimer assembly of human hemoglobin

We have investigated the effect of surface charge on the rate of assembly of alpha beta dimers of human hemoglobin A: alpha + beta k a----alpha beta. Heme intact beta A subunits were compared with four mutant subunits which differ by integral units of charge: beta N(Lys-95----Glu) (2-); beta J(Gly-16----Asp) (1-); beta S(Glu-6----Val) (1+); beta C(Glu-6----Lys) (2+). Subunit competition experiments were performed as follows. Varying amounts of 3H-labeled alpha A subunits were added to a mixture containing equal amounts of beta A and beta X subunits so that alpha/(beta A + beta X) ranged from 0.05-1.0. The reconstituted 3H-labeled Hbs A and X were analyzed by ion-exchange high pressure liquid chromatography as well as by gel electrofocusing and fluorography. Under the solvent conditions employed (10 mM PO4(Na), pH 7.0, 0 degrees C) a predominant proportion of the beta subunits was monomeric. Therefore, the ratio of Hb X to Hb A formed from subunit reconstitution when alpha/(beta X + beta A) approached zero provides a direct measure of the relative rates of monomer combination: kXa/kAa. The experimental values of this ratio decreased monotonically with the overall charge of the variant beta subunit: beta N = 2.6; beta J = 1.5; beta S = 0.41; beta C = 0.13. In contrast surface charge had no significant effect on the rate of dissociation of the alpha beta dimer: alpha beta kd----alpha + beta. At pH 8.0, where the alpha chains lack a net surface charge, they combined equally well to beta A and beta C chains. These experiments are consistent with a two-step mechanism, alpha + beta in equilibrium (alpha...beta) in equilibrium alpha beta, where the oppositely charged monomers diffuse together under the influence of their mutual electrostatic interaction to form a nonspecifically bound encounter complex [alpha...beta] that undergoes a surface charge-independent rearrangement to form the stable dimer.

Dissociation of dimers of human hemoglobins A and F into monomers

Dissociation of alpha beta and alpha gamma dimers of human hemoglobins (Hb) A and F into monomers was studied by alpha chain exchange (Shaeffer, J. R., McDonald, M. J., Turci, S. M., Dinda, D. M., and Bunn, H. F. (1984) J. Biol. Chem. 259, 14544-14547). Unlabeled carbonmonoxy-Hb A was incubated with trace amounts of preparatively purified, native, 3H-alpha subunits in 10 mM sodium phosphate, pH 7.0, at 25 degrees C. At appropriate times, free alpha monomers were separated from Hb A tetramers by anion exchange high performance liquid chromatography. Transfer of radioactivity from the alpha chain pool into Hb A was measured, yielding a first order dimer dissociation rate constant, k2 = (3.2 +/- 0.3) X 10(-3) h-1. The Arrhenius plot of k2 was linear between 7 and 37 degrees C, yielding an enthalpy of activation of 23 kcal/alpha beta dimer. As the chloride concentration was raised from 0 to 0.2 M, the dissociation rate increased 3-fold; with higher salt concentrations, however, the rate gradually returned to baseline. This rate was not altered by raising the pH from 6.5 to 7.2, but as pH was further raised to 8.4, kappa 2 increased about 3-fold. Hb F, which has an increased stability at alkaline pH, dissociated into alpha and gamma monomers 3 times more slowly than Hb A. Moreover, the dimer-monomer dissociation of Hb F was characterized by a significantly reduced pH dependence. These results demonstrate that both alpha beta and alpha gamma dimers of Hb A and Hb F dissociate reversibly into monomers under physiologic conditions. The differential pH dependence for dimer dissociation between Hb A and Hb F suggests that specific amino acid replacement at the alpha 1 gamma 1 interface confers increased resistance to alkaline denaturation.

Functional and subunit assembly properties of hemoglobin Alberta (alpha 2 beta 2(101) Glu----Gly)

Hemoglobin Alberta has an amino acid substitution at position 101 (Glu----Gly), a residue involved in the alpha 1 beta 2 contact region of both the deoxy and oxy conformers of normal adult hemoglobin. Oxygen equilibrium measurements of stripped hemoglobin Alberta at 20 degrees C in the absence of phosphate revealed a high affinity (P50 = 0.75 mm Hg at pH 7), co-operative hemoglobin variant (n = 2.3 at pH 7) with a normal Bohr effect (- delta log P50/delta pH(7-8) = 0.65). The addition of inositol hexaphosphate resulted in a decrease in oxygen affinity (P50 = 8.2 mm Hg at pH 7), a slight increase in the value of n and an enhanced Bohr effect. Rapid mixing experiments reflected the equilibrium results. A rapid rate of carbon monoxide binding (l' = 7.0 X 10(5) M-1 S-1) and a slow rate of overall oxygen dissociation (k = 15 s-1) was seen at pH7 and 20 degrees C in the absence of phosphate. Under these experimental conditions the tetramer stability of liganded and unliganded hemoglobin Alberta was investigated by spectrophotometric kinetic techniques. The 4K4 value (the liganded tetramer-dimer equilibrium dissociation constant) for hemoglobin Alberta was found to be 0.83 X 10(-6) M compared to a 4K4 value for hemoglobin A of 2.3 X 10(-6) M, indicating that the Alberta tetramer was less dissociated into dimers than the tetramer of hemoglobin A. The values of 0K4 (the unliganded tetramer-dimer equilibrium dissociation constant) for hemoglobin Alberta and hemoglobin A were also measured and found to be 2.5 X 10(-8) M and 1.5 X 10(-10) M, respectively, demonstrating a greatly destabilized deoxyhemoglobin tetramer for hemoglobin Alberta compared to deoxyhemoglobin A. The functional and subunit dissociation properties of hemoglobin Alberta appear to be directly related to the dual role of the beta 101 residue in stabilizing the tetrameric form of the liganded structure, while concurrently destabilizing the unliganded tetramer molecule.

Structural and functional studies of hemoglobin Wayne: an elongated alpha-chain variant

Hemoglobin Wayne (Hb Wayne) is a frame-shift, elongated alpha-chain variant that exists in two forms, with either asparagine or aspartic acid as residue 139. Oxygen equilibrium studies showed that stripped Hb Wayne Asn and Hb Wayne Asp possessed high oxygen affinity (P 1/2 = 0.60 and 0.23 mmHg at pH 7, respectively), were non-co-operative and have a markedly reduced Bohr effect (-delta log P 1/2/pH (7 to 8) = 0.34 and 0.10, respectively). Adding organic phosphate results in a decreased oxygen affinity and increased Bohr effect for both Hbs Wayne. The overall rate of carbon monoxide binding at pH 7 (l' = 5.6 X 10(6) M-1 S-1) was similar for both stripped Hbs Wayne and was 25-fold more rapid than that of stripped Hb A. When organic phosphate was added, Hb Wayne Asn exhibited a homogeneous slower rate of carbon monoxide binding (l' = 2.6 X 10(6) M-1 S-1), whereas Hb Wayne Asp showed heterogeneous binding (l' = 6.1 X 10(6) and 2.6 X 10(6) M-1 S-1 for fast and slow phases, respectively). The rates of overall oxygen dissociation and oxygen dissociation with carbon monoxide replacement for both Hbs Wayne were found to be slow compared to Hb A and uniquely different from each other. Similarly, sedimentation velocity experiments indicated that, although Hb Wayne Asn and Hb Wayne Asp were both less tetrameric than Hb A, each hemoglobin exhibited a distinct degree of oxygen-linked subunit dissociation. These observed differences in the allosteric properties of Hb Wayne Asn and Hb Wayne Asp appeared to be directly attributable to residue 139. The equilibrium and kinetic data are consistent with the X-ray diffraction analysis of Hb Wayne Asp, which shows that the C terminus of the deoxytetramers are severely disordered, a condition that results in major destabilization of the T conformation and disruption of normal hemoglobin function.

Dimer-monomer dissociation of human hemoglobin A

Isolated 3H-labeled human hemoglobin alpha chains were incubated with unlabeled carbonmonoxyhemoglobin A for 72 h in 0.01 M potassium phosphate, pH 7.0, at 25 degrees C. Following separation of the free alpha chain monomers and Hb A (alpha 2 beta 2) tetramers by electrophoresis on cellulose acetate strips or by chromatography on DEAE-cellulose columns, analysis of radioactivity showed a slow transfer of 3H-labeled alpha chains into Hb A. Separation of the globin chains of the isolated [3H] Hb A on a CM-cellulose column in 8 M urea showed that the radioactivity was in structurally intact alpha chains. Gel filtration of a reaction mixture on Sephadex G-75 in the presence of 0.15 M NaCl showed that the 3H-labeled alpha-chains in Hb A were an integral part of, and not nonspecifically adsorbed to, the tetramer. These results indicate that the free 3H-labeled alpha chain monomers were incorporated into Hb A by exchange with pre-existing unlabeled alpha chain subunits according to the scheme, alpha 2 beta 2 in equilibrium 2 alpha beta in equilibrium 2 alpha + 2 beta. The rate constant for the dissociation of alpha beta dimers to alpha and beta monomers, the rate-limiting step in this exchange reaction, was 4.0 (+/- 0.7) X 10(-3) h-1.

Electrostatic interactions in the assembly of haemoglobin

Haemoglobin is the prototype of an allosteric protein in which cooperative behaviour depends on interaction between unlike subunits. Here we present haematological and biochemical evidence that electrostatic interactions are an important determinant of haemoglobin assembly. Individuals heterozygous for positively charged beta-globin variants have a significantly lower proportion of abnormal haemoglobin than those with negatively charged variants. Moreover, these differences become more pronounced when alpha-thalassaemia is also present. Kinetic experiments using isolated chains indicate that the rate of assembly of the heterotetramer is influenced by alterations in surface charge. A simple electrostatic model is proposed in an attempt to explain these haematological and experimental findings.

The effect of pH on the rate of dissociation of the oxygenated beta chain tetramer of Hb A

The effect of pH on the overall assembly of oxyhemoglobin A following mixing of equivalent concentrations of alpha and beta heme subunits has been studied in 0.1 M potassium phosphate buffers at 20 degrees C. The resultant kinetic profiles monitored at 582.5 nm (the maximum of the oxyhemoglobin - oxy chain difference spectrum) were homogeneous and appeared to be first order. The rate of these exponential time courses, reflecting the rate of dissociation of the beta chain tetramer, increased from 0.013 min-1 at pH 6.4 to 0.30 min-1 at pH 8.0 and 1.0 min-1 at pH 8.5. Concurrent with this increased rate was a decrease in the overall color yield from the reaction. The absorbance changes, which involve a significant contribution from the beta chain tetramer to monomer dissociation step, changed three fold over the pH range studied. The findings indicate that protons enhance the stability of the beta chain tetramer.

Assembly of human adult and sickle hemoglobins from their oxygenated subunits. Differential rates of beta chain tetramer dissociation

The rate of assembly of oxyhemoglobins A and S at pH 7 and 20 degrees C has been followed spectrophotometrically at 582.5 nm, a maximum of the difference spectrum of isolated oxygenated subunits and intact oxyhemoglobin. In 0.1 M potassium phosphate buffer, the resultant time courses following mixing of equivalent concentrations of alpha and beta chains were homogeneous and followed first order kinetics. These time courses were protein concentration independent over a range of 8.0 to 60 X 10(-6) M in heme after mixing and presumably reflect the rate of dissociation of the beta chain tetramer. This rate-limiting dissociation reaction was found to be nearly 2-fold slower for the beta S than the beta A chain tetramer exhibiting half-times of 27 and 15 min, respectively. The overall rate of formation of Hb S and Hb A appears to be significantly influenced by the rates of dissociation of their respective beta chains. These findings are in contrast to mixing experiments done in 0.01 M potassium phosphate buffer which revealed time courses which were heterogeneous and markedly dependent upon protein concentration. The stability of the oxygenated beta chain tetramer and, therefore, the overall kinetic profile of liganded hemoglobin reconstitution is acutely sensitive to buffer conditions.

Structural analysis of the minor human hemoglobin components: Hb AIa1, Hb AIa2 and Hb AIb

Human hemolysate contains several minor hemoglobin components, including Hb AIa1, Hb AIa2, Hb AIb and Hb AIc which are post-translational modifications of the major component, Hb A0. Hb AIc is known to contain glucose attached to the N terminus of the beta chains by a ketoamine linkage. We separated the alpha and beta globin chains from purified Hb AIa1, Hb AIa2 and Hb AIb by ion-exchange chromatography. The beta chains were reducible by sodium borohydride and gave a positive thiobarbituric acid test. These results indicated that they are modified by ketoamine-linked carbohydrate. In addition, phosphate analysis revealed 1.5 phosphate residue associated with each beta AIa1 chain and 1 phosphate residue with each beta AIa2 chain. Hb AIa1, Hb AIa2 and Hb AIb were all found to be contaminated by non-globin proteins. Protein-sequencing approaches demonstrated that the N termini of beta AIa1, beta AIa2 and beta AIb were blocked. In support of this conclusion, analysis of tryptic digests of beta AIa2 and B AIb revealed modified N-terminal peptides. We conclude that, like Hb AIc, components Hb AIa1, Hb AIa2 and Hb AIb also contain a sugar moiety linked to the N terminus of the beta chain.

Nonenzymatic glycosylation of human hemoglobin at multiple sites

The most abundant minor hemoglobin component of human hemolysate is Hb A1c, which has glucose bound to the N-terminus of the beta chain by a ketoamine linkage. Hb A1c is formed slowly and continuously throughout the 120 day lifespan of the red cell. It can be synthesized in vitro by incubating purified hemoglobin with 14C-glucose. Other minor components, Hb A1a1 and Hb A1a2 are adducts of sugar phosphates at the N-terminus of the beta chain. Hb A1b contains an unidentified nonphosphorylated sugar at the beta N-terminus. In addition, a significant portion of the major hemoglobin component (Hb Ao) is also glycosylated by a glucose ketoamine linkage at other sites on the molecule, including the N-terminus of the alpha chain and the epsilon-amino group of several lysine residues on both the alpha and the beta chains. The results indicate that the interaction of glucose and hemoglobin is rather nonspecific and suggests that other proteins are modified in a similar fashion.