Influence of Cortisol on the Fibril Formation Kinetics of Aβ42 Peptide: A Multi-Technical Approach

Amyloid-β peptide (Aβ) aggregates are known to be correlated with pathological neurodegenerative diseases. The fibril formation process of such peptides in solution is influenced by several factors, such as the ionic strength of the buffer, concentration, pH, and presence of other molecules, just to mention a few. In this paper, we report a detailed analysis of in vitro Aβ42 fibril formation in the presence of cortisol at different relative concentrations. The thioflavin T fluorescence assay allowed us to monitor the fibril formation kinetics, while a morphological characterization of the aggregates was obtained by atomic force microscopy. Moreover, infrared absorption spectroscopy was exploited to investigate the secondary structure changes along the fibril formation path. Molecular dynamics calculations allowed us to understand the intermolecular interactions with cortisol. The combined results demonstrated the influence of cortisol on the fibril formation process: indeed, at cortisol-Aβ42 concentration ratio (ρ) close to 0.1 a faster organization of Aβ42 fragments into fibrils is promoted, while for ρ = 1 the formation of fibrils is completely inhibited.

P364 IMPORTANCE OF URIC ACID THRESHOLD IN ITS CORRELATION WITH METABOLIC SYNDROME

Background

The relationship between Hyperuricemia and Cardiovascular risk has been established but whether or not a correlation between Serum Uric Acid (SUA) and Metabolic Syndrome (MS) exists is still a matter of debate. Indeed whether SUA level is part of MS diagnosis or just a pure marker of an unfavourable metabolic profile has not been demonstrated. Besides it’s unknown whether SUA’s addition to MS definition makes a difference in terms of prognosis. In our study we focused on evaluating in a group of hypertensive patients, the correlation between MS diagnosis and SUA defined with two different cut–off: 1) ≥6 mg/dL for women and ≥7 for men (classic cut–off); 2) >5.6 mg/dL for both sexes (recently proposed by the URRAH Project).

Methods

We enrolled 473 Hypertensive patients followed by the Hypertension Unit of San Gerardo Hospital (Monza, Italy), in which SUA was measured. Patients with Hyperuricemia were identified according to the two different thresholds. NCEP–ATP–III criteria were used for diagnosis of MS.

Results

MS was diagnosed in 33.6% while Hyperuricemia was found in 14.8% of subjects according to the traditional cut–off and 35.9% according to URRAH study’s cut–off. Hyperuricemia and MS coexist in 9.7% (traditional cut–off) and 17.3% (URRAH’s threshold) of the population. Hyperuricemia was more frequent in MS than in non–MS subjects (29 vs 7.6%, p–value<0.0001 for cut–off 6/7 mg/dL and 51.6 vs 28.0%, p–value<0.0001 for cut–off 5.6 mg/dL). Linear regression models showed that SUA is related to MS diagnosis (β = 1.597, p–value<0.0001). At logistic analysis Hyperuricemia was strongly related to MS when defined by the HURRAH‘s cut–off (OR = 0.303, p–value<0.0001). The same relation is weak, although significan, when Hyperuricemia was defined by the classic cut–off (OR = 0.182, p–value<0.0001).

Conclusions

Hyperuricemia is related with MS diagnosis especially when defined by the recently defined cut–off of 5.6 mg/dL.

Normal mode calculation and infrared spectroscopy of proteins in water solution: Relationship between amide I transition dipole strength and secondary structure

Dipole Strength (DS) of the amides has gained a renewed interest in chemical physics since it provides an important tool to disclose the on-site vibrational energy distributions. Apart from earlier experimental efforts on polypeptides, little is still known about DS in complex proteins. We accurately measured the Fourier Transform Infrared absorption spectra of nine proteins in water solution obtaining their Molar Extinction Coefficient in the amide I and II spectral region. Our results show that the amide I DS value depends on the protein secondary structure, being that of the α-rich and unstructured proteins lower by a factor of 2 than that of the β-rich proteins. The average DS for amino acids in α and β secondary structures confirms this finding. Normal Mode calculation and Molecular Dynamics were performed and used as tools for data analysis and interpretation. The present outcomes corroborate the hypothesis that antiparallel β-sheet environment is more prone to delocalize the on-site CO stretching vibration through coupling mechanisms between carbonyl groups, whereas α-helix structures are energetically less stable to permit vibrational mode delocalization.

The Puzzling Problem of Cardiolipin Membrane-Cytochrome c Interactions: A Combined Infrared and Fluorescence Study

The interaction of cytochrome c (cyt c) with natural and synthetic membranes is known to be a complex phenomenon, involving both protein and lipid conformational changes. In this paper, we combined infrared and fluorescence spectroscopy to study the structural transformation occurring to the lipid network of cardiolipin-containing large unilamellar vesicles (LUVs). The data, collected at increasing protein/lipid ratio, demonstrate the existence of a multi-phase process, which is characterized by: (i) the interaction of cyt c with the lipid polar heads; (ii) the lipid anchorage of the protein on the membrane surface; and (iii) a long-distance order/disorder transition of the cardiolipin acyl chains. Such effects have been quantitatively interpreted introducing specific order parameters and discussed in the frame of the models on cyt c activity reported in literature.

Cytochrome c aggregation: A dataset at and far from the isoelectric point

We present SEM, ThT fluorescence and circular dichroism (CD) data of amyloidogenic aggregates of cytochrome c (cyt c).This protein is of outmost relevance in many biochemical processes, such as respiratory chain in mitochondria and cells apoptosis. The present data focus on polymorphism of the protein aggregates obtained at the isoelectric point (IP) and by changing the environmental pH above and below the IP, the protein concentration and the base. The SEM images provide evidence for a large variety of structures, depending on the pH and on protein concentration: mature amyloid fibrils and overstructured platelets are distinguishable in the aggregates below IP, and relatively high cyt c concentration, whereas inhomogeneous amyloid formations are observed above it. At pH 10, i.e. close to IP, only characteristic protein particulates at the micrometric scale are observed. SEM and Fluorescence data have been acquired in dried drops of protein solution, prepared in different bases: TRIS-HCl, at the different pH values, or NaOH (pH 13). Along with this, at relatively low cyt c concentration compact layered structures are visible below the IP, though still made of a thin fibrils reticulate, whereas above the IP, also at low cyt c concentration, granulates structures are present, merging into compact layer, alongside with platelets and mature fibers. These areas are characterized by diffuse ThT-fluorescence and typical fibrils. The loss of the predominant alpha helix secondary structure was verified by CD spectra. Besides the intrinsic scientific relevance, this data collection provides a set of images useful for spectroscopists to discriminate among different morphologic protein formations and suggests pathways for the achievement of different kinds of cytochrome c aggregates.

These data are add-ons of the paper published in the International Journal of Biomacromolecules, 138 (2019) 106–115, https://doi.org/10.1016/j.ijbiomac.2019.07.060.

Cytotoxic chemotherapy in the treatment of advanced renal cell carcinoma in the era of targeted therapy

BACKGROUND

Renal cell carcinoma (RCC) is a heterogeneous disease with regards to histology, progression, and response to treatment. Cytotoxic chemotherapy has been extensively studied in metastatic RCC (mRCC). Responses in most studies are modest and the mechanisms of resistance remain poorly understood. Targeted therapies have significantly improved outcomes in mRCC; however, most patients eventually relapse and die of their disease. Early clinical data suggest that combinations of chemotherapy and targeted agents are clinically active and are well tolerated.

METHODS

We reviewed the available literature for published clinical trials incorporating traditional chemotherapeutic agents in the treatment of mRCC. These papers were identified through a Medline search and were included if they employed at least one chemotherapeutic agent in the treatment of mRCC. The literature was also reviewed for information regarding mechanisms of chemotherapy resistance.

RESULTS

The data regarding the use of cytotoxic chemotherapy in mRCC consist of small, non-randomized phase I and II studies. The major response proportions with single agent chemotherapies are low but combination regimens either with other cytotoxic agents, cytokines, or targeted agents have demonstrated moderate activity. Disparate trial designs and lack of head to head clinical trials make it difficult to compare the efficacy of chemotherapy with that of immunotherapy or targeted agents. Chemotherapy is particularly useful in patients with collecting duct histology and predominantly sarcomatoid differentiation. Chemotherapy resistance may be mediated by overexpression of p-glycoprotein efflux pumps and the dysregulation of the microtubule-hypoxia inducible factor signaling axis.

CONCLUSIONS

The role of cytotoxic chemotherapy in the treatment for clear cell RCC remains poorly defined. Cytotoxic chemotherapy is considered a standard of care in patients with mRCC with predominantly sarcomatoid differentiation and collecting duct RCC variants (Motzer et al., 2014). Early trials combining chemotherapy with targeted therapies are generally well tolerated and show clinical activity. A better understanding of the biology of aggressive subsets of RCC and mechanisms of resistance will help elucidate the role of cytotoxic agents in the current treatment paradigm of RCC.

7S Globulins fromPhaseolus vulgarisL.: Impact of Structural Aspects on the Nutritional Quality

7S globulins were extracted from common bean (Phaseolus vulgaris L.) seeds and characterized. SDS-PAGE showed major bands corresponding to the phaseolin subunits (43-53 kDa). An amino acid analysis indicated that, in spite of the limited amounts of sulphur amino acids and tryptophan, the globulins contained very high levels of essential amino acids. The protein solubility profiles of native and denatured (120 degrees C for 20 min) 7S globulins in water and in 0.5 M NaCl showed that NaCl had a limited effect on increasing the solubility of either the native or denatured proteins. The in vivo small intestinal digestibility of the 7S globulins was 90%, this being decreased to 86% after a thermal treatment. Fourier transform infrared spectroscopy revealed a high content of beta-sheet and beta-turn structures, together with a contribution at 1687 cm(-1) that was assigned to intramolecular beta-sheets. These features are diagnostic of a high propensity to irreversible aggregation that may be related to an adverse effect on the protein quality.

Epicatechin-induced conformational changes in β-lactoglobulin B monitored by FT-IR spectroscopy

ABSTRACT

The interaction between whey carrier protein β-lactoglobulin B and (-)-epicatechin, a major dietary flavonoid with a wide range of health-promoting biological activities, was investigated by Fourier transform infrared spectroscopy in physiological conditions. Amide I spectra of epicatechin - β-lactoglobulin complexes, in D2O buffer solutions, pD= 6.8, at molar ratios from 0.5:1 to 15:1, were measured by using a cell device specifically created. Changes in secondary structure elements at increasing epicatechin concentrations were quantified. Two different trends were observed for the intensities of β-sheet, random coil, and side chain contributions. At molar ratios ≤2 the β-exposed strand contributions (1625 cm(-1)) increased at the expence of the β-antiparallel sheet band (1637 cm(-1)). At molar ratios >2 the intensities of both β structures slightly decreased. The same behaviour was observed for the side chain contributions (band around 1610 ÷ 1620 cm(-1)). In addition, a conformational transition to a slightly opened structure, followed by aggregate formation at the highest molar ratios, were revealed. The results suggest that binding of epicatechin to β-lactoglobulin in physiological conditions occurs at the surface of the protein molecule, resulting in protein dissociation at molar ratios ≤2 with minor changes in secondary structure. This finding provides further evidence for the possibility of successful use of the protein as a carrier of flavonoids, epicatechin included.

Bioactive molecules and antioxidant activity in durum wheat grains and related millstream fractions

The present study was performed to evaluate the distribution of phytochemicals in wheat grains and millstreams and the contribution of these compounds to the antioxidant activity. Bioactive molecules, although related to genotype, were highly affected by the milling procedure applied. Carotenoids were unevenly distributed in the kernel and lutein resulted to be the main carotenoid in all samples considered. The WSB method was confirmed to be a useful tool to detect yellow color intensity of semolina but it was not suitable to get information on the true content of carotenoids of the sample. Water-methanol soluble components showed antioxidant activity which decreased from the outer to the inner parts of the kernel. Chloroform-methanol soluble compounds showed generally negligible or negative antioxidant activity due to the inadequate amount of antioxidants unable to counteract oxidative processes already in progress.

Application of two-dimensional electrophoresis for monitoring gastrointestinal digestion of milk

Two-dimensional electrophoresis (2-DE) was used for tracing in vivo gastrointestinal digestion of milk proteins in a rapid model system with rats. Contents of stomach and small intestine from digestion trials with rats given a single dose of milk powder were recovered after 1 hour. They were then subjected to 2-DE (IEF and SDS-PAGE). 2-DE showed undigested proteins in a MW range 13.0-66.0 kDa in stomach and 13.0-25.0 kDa in the small intestine, thus indicating that milk proteins are slowly digested. This approach may shed light on pattern of protein digestion and mechanism of amino acid and peptide assimilation.

Absorption of Quercetin and Rutin in Rat Small Intestine

BACKGROUND/AIMS

Dietary antioxidant flavonoids, especially flavonols, are ubiquitous constituents of plant foods with potential health-promoting effects. However, the actual bioavailability of these compounds in vivo, especially in the prevalent glycosidic form, remains a controversial point in making an assessment of their biological importance. Thus, absorption of quercetin and rutin in the small intestine has been determined.

METHODS

The bioavailability of quercetin and rutin (quercetin-3-rutinoside) was assessed in vivo, with single-meal experiments with rats and by an in vitro method with ligated loops of rat small intestine. The amount of quercetin or rutin in the plasma of rats or in the lumen of each intestinal segment was assayed by maximum absorption in the UV/VIS optical spectrum as was the amount of compound that had crossed the gut wall into the incubation buffer. In addition, uptake of [14C]quercetin was tested in vitro.

RESULTS

Absorption of both quercetin and rutin from the small intestine of rat was evident. However, rutin appeared to be absorbed more slowly than quercetin. Experiments with [14C]quercetin showed that only 1.5% quercetin crossed the gut wall in vitro and more than half of the total quercetin was bound to the small intestinal tissue.

CONCLUSIONS

Both quercetin and rutin can attach to and traverse the small intestine of the rat. Binding of flavonoids to the intestinal wall components may however greatly limit their absorption from the small intestine.

Modulation of antioxidant compounds in organic vs conventional fruit (peach, Prunus persica L., and pear, Pyrus communis L.)

Despite the increasing interest in organic products, knowledge about how different levels of fertilization affect nutritionally relevant components is still limited. The concentration of polyphenols and the activity of polyphenoloxidase (PPO), together with the content in ascorbic acid, citric acid, and alpha- and gamma-tocopherol, were assayed in conventional and organic peach (Prunus persica L., cv. Regina bianca) and pear (Pyrus communis L., cv. Williams). 2-Thiobarbituric acid reactive substances and the tocopherolquinone/alpha-tocopherol ratio were used as markers of oxidative damage in fruits. A parallel increase in polyphenol content and PPO activity of organic peach and pear as compared with the corresponding conventional samples was found. Ascorbic and citric acids were higher in organic than conventional peaches, whereas alpha-tocopherol was increased in organic pear. The concentration of oxidation products in organic samples of both fruits was comparable to that of the corresponding conventional ones. These data provide evidence that an improvement in the antioxidant defense system of the plant occurred as a consequence of the organic cultivation practice. This is likely to exert protection against damage of fruit when grown in the absence of pesticides.

Evaluation of polyphenol bioavailability in rat small intestine

BACKGROUND

Dietary polyphenols, which are contained in several foods of plant origin, have been reported to be effective protective agents against cardiovascular diseases and cancer. However, data on their absorption from the gastrointestinal tract are still scarce and, often, contradictory.

AIM OF THE STUDY

In this report, evaluation of polyphenol bioavailability was carried out by using segments of the small intestine from rat. The extent of absorption throughout the small intestine of rat was evaluated with two model compounds, tannic acid and catechin, as representatives of high and low molecular weight polyphenols, respectively. The consequence of the binding of tannic acid to BSA on both tannic acid absorption and in vivo protein digestibility was also examined.

METHODS

Polyphenol solutions of different concentrations were injected into the lumen of ligated segments (6 cm) of the small intestine and the segments incubated in buffer for 5 min. The residual amount of polyphenol in the lumen of each segment was assayed by maximum absorption in the UV/VIS optical spectrum as was the amount of compound that had crossed the gut wall into the incubation buffer. Digestibility of BSA and of a BSA- tannic acid complex was assayed with rats.

RESULTS

The results indicated a significant, concentration-dependent, disappearance of both polyphenols from the small intestine of the rat, with higher uptake levels being evident for tannic acid (50%) than catechin (30%). However, complete transfer through the gut wall was not observed with tannic acid whilst low but significant amounts (10%) were detected in incubation buffers with catechin. Partial binding of polyphenols by endogenous proteins in the intestinal lumen was also demonstrated. Complexing tannic acid with BSA (1:10 mol/mol) was not found to affect either the extent of interaction of tannic acid with the small intestine or the in vivo digestibility of the protein.

CONCLUSIONS

Our experiments show that tannic acid and catechin both interact with the gut but only catechin appears able to traverse the gut. In addition, they provide evidence for binding of tannic acid and catechin by endogenous proteins in the intestinal lumen. This may limit their absorption from the small intestine. BSA complexed with tannic acid was as readily digested as BSA alone. This may suggest that tannic acid exerts anti-nutritional effects by binding to proteins of the gut wall and interfering with gut function rather than by inhibition of dietary protein digestion.

Investigation of the mechanisms affecting Cu and Fe bioavailability from legumes: role of seed protein and antinutritional (nonprotein) factors

Chemical composition and content in polyphenols, phytic acid, and dietary fiber of whole cooked common bean (Phaseolus vulgaris L.) and faba bean (Vicia faba L.) and of soluble and insoluble fractions separated from them were determined. Simultaneous determination of Cu, Fe, and protein bioavailability in the small intestine of rat was carried out in single-dose, short-term (1 h) experiments. After cooking, about 80% of seed components (on a weight basis) of either legume was recovered in the precipitate (insoluble fraction) after extraction with water. Protein, lipid, starch, dietary fiber, and polyphenols underwent the most severe insolubilization, together with more than 70% of total Cu and Fe. Cu, Fe, and protein bioavailability showed a similar trend (i.e., the lower the protein, the lower the Cu and Fe availability). Availability of proteins, Cu, and Fe in the insoluble fractions were the lowest, but Cu bioavailability was higher than that of Fe in all fractions. The results provide evidence that the heat-induced insolubilization process adversely affects not only protein but also Cu and Fe bioavailability from legumes and that polyphenols are likely to be a major inhibitor on absorption.

Composition and calcium status of acid whey from pasteurized, UHT-treated and in-bottle sterilized milk

Whey extracts were obtained from pasteurized, UHT-treated and in-bottle sterilized milks. After acidic precipitation of casein the concentration of protein, NPN, lactose, lipid, calcium, magnesium and potassium was determined. Among the parameters examined, protein content was significantly reduced in the whey extracts from UHT-treated and in-bottle sterilized milks compared with that from pasteurized milk, while lactose content was increased. Calcium extracted in whey was at least 80% of total calcium of the milk. The total calcium to protein ratio of whey was increased as a function of the thermal treatment of milk, while ionic calcium was about 50% of total calcium in all whey extracts. In vitro protein digestibility was found to be significantly lower in whey from UHT-treated and in-bottle sterilized milks than in that from pasteurized milk. Parallel estimation of the percentage of ionic calcium and of the solubility of proteins in the pH range 2-10 indicated that calcium was not involved in the pH-dependent solubility of proteins extracted in the whey, the extent of solubility being essentially a function of the thermal treatment of milk. The results suggest that calcium was not responsible for the formation of soluble protein macroaggregates with impaired digestibility that are present in whey from milk subjected to heat treatment of increasing intensity.

Perspectives into factors limiting in vivo digestion of legume proteins: antinutritional compounds or storage proteins?

The in vivo protein digestibility of raw and cooked common bean (Phaseolus vulgaris L.) and faba bean (Vicia faba L.) and of protein fractions extracted from them was determined with growing rats. Overnight-fasted rats were intubated with a protein suspension or fed the same amount of protein added to a basal diet. The rats were killed 1 h later, the contents of stomach and small intestine were washed out, and their protein contents were measured. The in vivo digestibility of proteins of raw common bean flour was 72.4% and not significantly improved after cooking. In contrast, the digestibility of faba bean proteins was decreased from 86.5 to 60.6% by the thermal treatment. Globulins from either species had similar digestibilities (approximately 70%). Proteins in the soluble fraction of cooked beans were more digestible than those in the insoluble fraction, which contained the bulk of the proteins. Hemagglutination assay and trypsin inhibitor determination indicated that after the thermal treatment only very low, nonharmful, levels of both lectin and inhibitor remained. Faba bean contained more polyphenols than common bean samples, with most of the polyphenols being bound to globulins. However, protein-bound polyphenols were markedly decreased after cooking. SDS-PAGE characterization of the gastrointestinal digesta of globulins and amino acid analysis of undigested proteins of whole cooked common bean and faba bean suggested that it is mainly the structural properties of the storage proteins and not their binding of polyphenols, which determines the extent of protein aggregation on autoclaving and may therefore be responsible for their low digestibility.

Heat-induced aggregation of Phaseolus vulgaris L. Proteins: an electron spin resonance study

The mechanism of heat-induced aggregation of Phaseolus vulgaris L. proteins and of subunit interactions of importance for susceptibility of proteins to proteolysis was studied by electron spin resonance (ESR) spectroscopy. The mobility of a spin label bound to lysine residues was monitored at two different pH-induced (neutral and alkaline) association states of proteins extracted from raw and cooked common bean. The molecular weight of the protein complexes was assessed by size exclusion-high performance liquid chromatography (SE-HPLC) of labeled proteins. Upon alkaline dissociation, both native and denatured protein subunits underwent a reassociation process to form soluble complexes of molecular weight higher than the species originally present at neutral pH. However, unlike native proteins, impaired mobility of the spin label was observed in the aggregates that are formed after dissociation of subunits of denatured proteins, indicating a reduced accessibility of lysine residues. Trapping of lysine residues inside protein aggregates may explain limited digestibility in the small intestine of proteins in cooked legumes.

Relationship between in vitro Fe and Zn dialysability and peptide composition of albumin and globulins extracted from cooked bean (Phaseolus vulgaris L.)

In vitro dialysability of iron, zinc and protein was determined from whole bean (Phaseolus vulgaris), albumin and globulin (G1, G2) after cooking. Albumin showed the highest iron, zinc, protein and phytic acid content. Cooking increased iron and protein dialysability only in whole bean and albumin. Compared to globulins, albumin also presented a higher in vitro protein digestibility and cystine chemical reactivity. HPLC analysis of peptides in dialysates of bean and protein fractions suggested that some aggregation occurred during dialysis. The percentage of amino acids in dialysed peptides was found to be different between albumin and globulins. The difference in iron and zinc dialysability between albumin and globulins seems to depend on the phytic acid content of the albumin fraction and the protein properties of globulins.

The interaction of ceruloplasmin with Kupffer cells

The binding and uptake of ceruloplasmin was studied with rat liver cells using gold-labeled probes. Ceruloplasmins from either rat or sheep were used, in which different molecular conformations had been induced according to established biochemical criteria. The native protein from either species could bind not only to the endothelium, but also to Kupffer cells, at variance with previous findings. The proteins which had been converted to the conformation typical of stored molecules--which can be considered aged, but not denatured, according to standard activity and spectroscopic assays--were bound by endothelium irrespective of species, while only rat ceruloplasmin was able to bind to rat Kupffer cells. Internalization of sheep ceruloplasmin occurred with either endothelium or Kupffer cells. This property was lost with isolated suspended Kupffer cells. These findings suggest the presence of receptors for ceruloplasmin on Kupffer cells which are different from those present on endothelial cells.

Unusual stability properties of a reptilian ceruloplasmin

Ceruloplasmin from the turtle Caretta caretta was isolated to purity by using the single-step procedure recently developed by us to purify sheep and chicken ceruloplasmin. It has a Mr of ca. 145,000 and a total copper content of 5.1 +/- 0.2 atoms of copper per molecule, 50% of which are detectable by EPR. The spectroscopic features include an absorption maximum at 603 nm in the electronic spectrum and the total absence of any resonance attributable to Type 2 copper in the EPR spectrum. Turtle ceruloplasmin was found to be unusually resistant to aging and proteolysis, when compared to ceruloplasmins isolated from other species. p-Phenyl-endiamine oxidase activity measurements revealed an unusually low catalytic efficiency, while the kinetic parameters of Fe(II) oxidation were consistent with those reported for other species of ceruloplasmin.

Presence of coupled trinuclear copper cluster in mammalian ceruloplasmin is essential for efficient electron transfer to oxygen

The reactivity with dioxygen of a mammalian (sheep) ceruloplasmin, anaerobically reduced with ascorbate, was found to depend on the state of the Type 2 and Type 3 copper centers, as monitored by EPR and optical spectroscopy. A complete reoxidation by air after anaerobic reduction with ascorbate was observed with samples (A) purified by the single-step procedure described for chicken ceruloplasmin (Calabrese, L., Carbonaro, M., and Musci, G. (1988) J. Biol. Chem. 263, 6480-6483), while samples prepared by traditional multistep procedure (B) or subjected to freeze-thawing (C) displayed partial and very slow reoxidation, reflecting the functional nonequivalence of blue coppers which is considered a typical property of mammalian ceruloplasmin. The rate of reduction of the 330 nm chromophore was found to increase as a function of the extent and rate of reoxidation of different samples, while the 610 nm band displayed an opposite trend. Samples B and C showed a Type 2 copper signal in the EPR spectrum, while sample A showed practically no Type 2 copper in the oxidized protein, and a transient Type 2-like signal during reduction. The presence of a trinuclear Type 2-Type 3 cluster can therefore be proposed for all ceruloplasmins, and the integrity of the copper-copper coupling is essential for efficient oxidase behavior.

Chicken ceruloplasmin. Evidence in support of a trinuclear cluster involving type 2 and 3 copper centers

Ceruloplasmin was isolated to purity from chicken plasma by a single-step chromatography on amino-ethyl-derivatized Sepharose. Molecular mass, as estimated by nonreducing sodium dodecyl sulfate-electrophoresis, was approximately 140 kDa, slightly higher than that found for ceruloplasmins from other sources. Specific activity as p-phenylenediamine oxidase was five times higher than that reported for mammalian ceruloplasmins. The copper content was estimated to be 5.01 +/- 0.35 atoms per protein molecule, 50% of which was EPR-detectable. The EPR spectrum was completely devoid of any signal typical of the type 2 copper as seen in the other blue multicopper oxidases and in ceruloplasmin from mammalian species. Anaerobic reduction of chicken ceruloplasmin resulted in the disappearance of the 330 nm optical band typical of type 3 copper, which was followed by the appearance of an EPR signal typical of type 2 copper. Subsequently, the type 1 copper and finally the newly formed type 2 copper were reduced. The original optical and EPR spectra were recovered within few minutes upon exposure of reduced ceruloplasmin to air. It is concluded that in oxidized chicken ceruloplasmin type 2 copper interacts with the diamagnetic pair responsible for the 330 nm absorption in such a way as to become EPR-undetectable and that the interaction is relieved by reduction of the pair. Whether this interaction is intrinsically weaker in other blue oxidases and ceruloplasmins studied or is lost with standard preparation procedures remains to be established.

Evaluation of factor VII antigen in factor VII congenital deficiencies with a new ELISA assay

An evaluation of a new Enzyme Linked Immunosorbent Assay (ELISA) factor VII:Ag assay in factor VII congenital deficiencies was carried out. This assay was compared to factor VII:C assay and the Inhibitor Neutralization Assay (INA) for factor VII:Ag, both in normals and F VII-deficient patients. The correlations between ELISA F VII:Ag and VII:C, as well as the one between INA F VII:Ag and VII:C, were good (r = .86 and .81, respectively). The correlation between the two immunologic methods of assay in normals was fairly good (r = 0.73, P less than 0.001); whereas in mild F VII deficiencies (heterozygotes for F VII deficiencies), the two methods correlated very well (r = .96). In the severe deficiencies, ELISA F VII:Ag assay allowed the evaluation of F VII protein levels below 1 u/dl. The sensitivities of the INA and ELISA assays were evaluated by creating artificially prepared plasmas containing serial amounts of purified F VII: INA was unable to pick up F VII protein levels lower than 75 ng/ml, whereas the ELISA assay could detect up to 5 ng of F VII.

An e.p.r. study of the non-equivalence of the copper sites of caeruloplasmin

The two Type 1 (blue) copper-binding sites of caeruloplasmin were spectroscopically differentiated by the kinetic analysis of the e.p.r. spectra during the redox cycle. One blue copper, with a hyperfine splitting constant (A parallel) of 6.8 mT, which was rapidly reduced, was not reoxidized by oxygen, whereas it was reoxidized by H2O2. The other blue copper (A parallel = 5.8 mT), which was reduced slowly, was rapidly reoxidized by either oxygen or H2O2. A conformational change of the Type 2 copper was concomitant with the fast reduction of Type 1 copper, whereas its reduction occurred during the slow phase. This sequence of events was reversed in the reoxidation step, that is, the Type 2 copper reappeared rapidly as the species with altered conformation and reverted to the symmetry typical of the native state in the slow phase. The specific reaction of a blue-copper site with the H2O2 can tentatively be related to the established ability of caeruloplasmin to prevent 'oxidative' attack of proteins and lipids.