Fusion hindrance for a positive-q-value system (24)Mg+(30)Si.

Measurements of the excitation function for the fusion of (24)Mg+(30)Si (Q=17.89 MeV)have been extended toward lower energies with respect to previous experimental data. The S-factor maximum observed in this large, positive-Q-value system is the most pronounced among such systems studied thus far. The significance and the systematics of an S-factor maximum in systems with positive fusion Q values are discussed. This result would strongly impact the extrapolated cross sections and reaction rates in the carbon and oxygen burnings and, thus, the study of the history of stellar evolution.

Neutron pair transfer in (60)Ni+(116)Sn far below the Coulomb barrier.

An excitation function of one- and two-neutron transfer channels for the ^{60}Ni+^{116}Sn system has been measured with the magnetic spectrometer PRISMA in a wide energy range, from the Coulomb barrier to far below it. The experimental transfer probabilities are well reproduced, for the first time with heavy ions, in absolute values and in slope by microscopic calculations which incorporate nucleon-nucleon pairing correlations.

The slopes of sub-barrier heavy-ion fusion excitation functions shed light on the dynamics of quantum tunnelling.

Quantum tunnelling plays a crucial role in heavy-ion fusion reactions at sub-barrier energies, especially in the context of nuclear physics and astrophysics. The nuclear structure of the colliding nuclei and nucleon transfer processes represent intrinsic degrees of freedom. They are coupled to the relative ion motion and, in general, increase the probability of tunnelling. The influence of couplings to nucleon transfer channels relatively to inelastic excitations, on heavy-ion fusion cross sections, is one of the still open problems in this field. We present a new analysis of several systems, based on the combined observation of the energy-weighted excitation functions E σ in relation to their first energy derivatives d ( E σ ) / d E . The relation between d ( E σ ) / d E and E σ removes the basic differences due to the varying Coulomb barrier when comparing different systems. We show that, depending on the nuclear structure and/or the presence of strong transfer channels, this representation reveals characteristic features below the barrier. The possible presence of cross section oscillations makes this analysis less clear for light- or medium-light systems.

Specificity in protein-ligand interactions: a model from estrone-antiserum binding.

The specificity of protein-ligand interactions has been investigated using the binding of structurally related steroids to a polyclonal anti-estrone antiserum as a model. The cross-reaction profile of the native antiserum was compared with profiles obtained for the same antiserum preparation following affinity separation on stationary phases carrying structures which mimic parts of the antigen molecule: the coupling bridge, the A ring of the estrogen and the carrier protein. This fractionation produced antibody mixtures with different specificities from that observed for the pre-affinity antiserum. The changes in specificity observed and, more importantly, the direction of each variation detected, suggested the basis for a description of the nature of molecular recognition of small ligands by a protein as discrete rather than continuous. This methodology has revealed some recognition mechanisms.

Time resolved fluoroimmunoassay of 7-methyl-2'-deoxyguanosine imidazole (ring open).

A solid-phase competitive time-resolved fluoroimmunoassay for 7-methyl-2'-deoxyguanosine imidazole (ring open) is described, based on highly specific hemocyanin carrier rabbit antibodies, modified with europium chelates. Eu3+ photoluminescence was detected in a novel micellar solution. The assay was validated both by comparing it with an ELISA and by analysing DNA samples, alkylated either 'in vitro' or 'in vivo' by dimethyl sulfate. The proposed assay proved to be sensitive, simple and reliable. It should be of value, together with other immunoassays for methylated DNA bases, in assessing human environmental exposure to alkylating agents such as nitrosamines, thereby providing a powerful tool in epidemiological investigations.

Highly specific polyclonal antisera against estriol: cross-reactivity restriction following affinity chromatography.

An immunosorbent technique was developed to attenuate cross-reactivity of a polyclonal antiserum against a 4(2) (rho-carboxyphenylazo)-1,3,5[10]-estratrien-3,16 alpha,17 beta-triol-bovine serum albumin conjugate. The chromatographic separation of antiserum through stationary phases having either rho(carboxymethyl)phenylazo-phenol or rho(carboxymethyl)-phenylazo-2-naphthol side residues reduced the antiserum avidity, while increasing the apparent antiserum affinity and decreasing the residual cross-reactivities against heterologous ligands. The highly specific antiserum obtained allowed the development of a competitive binding assay over an extended analytical range, which opens up the possibility of direct measurement of estriol from the early pregnancy to delivery. The significance of the attenuation of antiserum cross-reactions after affinity chromatography is discussed with reference to epitope-paratope interaction in the case of small endogenous molecules like estrogens.

Relevance of oestrone presentation to the specificity of the elicited antisera, as revealed by affinity separation.

Polyclonal antisera raised against two different azobenzoyl-oestrone derivatives were analysed to investigate both the latency/intensity relationship of the immune response and the influence of antigen presentation on the specificity of the antisera elicited. Elongation of the azo-bridge of the hapten ([p(carboxyphenyl)-azo]-1,3,5[10]- oestratrien-3 ol-17 one) with a short aliphatic chain (4-amino-n-butyric acid) resulted in a marginal increase in the antibody yield, without affecting the time required to attain the maximum titre. The increased flexibility and mobility of the extended azo-bridge was shown to result in the appearance of antisera which cross-reacted with oestrogens with D ring structures different to that of oestrone. Antiserum fractionation by affinity chromatography through a stationary phase exposing the carrier protein determinants, as modified by the addition of the coupling bridge and the phenol ring, resulted in a reduction in its specificity. These findings are discussed with regard to the phenomena underlying the specificity of a polyclonal antiserum.

Time-resolved fluoroimmunoassay.

A method is reported to set up a standard competitive TR-FIA. A simple and inexpensive way to prepare reagents and carry out operations is presented as well, with the aim to make it possible to perform a very sensitive analytical procedure in a personalized way within a nondedicated biochemistry laboratory. This protocol is general and can be easily modified with consideration to the analytical target. Once the antibody is available, both its labeling with diethylenetriaminepentaacetic acid dianhydride and Eu3+, and the setting-up of the assay with measurement of europium ion time-resolved fluorescence in a home-made enhancement solution become feasible.

A source of false-negative results in clenbuterol analysis in tissues of veal calves.

The possibility of false-negative results in clenbuterol analysis was investigated in bovine tissues. An extraction procedure currently in use was adapted to process 100 specimens of different tissues each time. Its efficiency and accuracy were investigated radiometrically by means of a series of different molar concentration of the tritiated drug. In samples not submitted to extensive delipidation, unreliability of the analysis was evident. The measurement of tissue clenbuterol content, by a competitive ELISA, gave results numerically similar to those existing in literature, but with an accuracy high enough to minimize the frequency of false-negative results.

Photomodulated azoaldolase: a model for light intervention in biological systems?

Azoaldolase is obtained from rabbit muscle aldolase by adding an azo chromophore to a cysteine side chain in each of the four enzyme subunits. The enzyme becomes photosensitive whereas both its catalytic activity and the michaelian kinetics are retained. Chromophore excitation causes E to Z isomerization of the azo bond, and mutually influences the protein-substrate equilibria. The various isomerization and substrate binding equilibria have been investigated under the hypothesis of a cyclic process described by four linked equilibrium constants. The mechanism of the light effect is a continuous adaptation of the specific parameters of the active protein, that is substrate recognition and rate of the catalyzed process. Absorbed light allows the rapid modification of the concentrations of various related molecules, depending on the used frequencies. At present such a mechanism has not been described in photobiology; so azoaldolase can be taken as a model for a possible new mechanism of light regulation of a biological system, based on changes in the molecular recognition by an active protein against its substrate.

Immunological and biochemical evidence that blepharismin is not a prosthetic group.

A polyclonal, multispecific antiserum was raised against a whole 3[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate-extract of nonirradiated Blepharisma japonicum cells. It was used to reveal the composition of solutions that were hypothesized to contain the photoreceptor of the ciliate. A Bio-Gel A 1.5 m fine column chromatography of the extract allowed recovery of a single elution peak isolated by recording the 580 nm light absorbance. Fused-rocket immunoelectrophoresis of this material revealed a large number of > 300 kDa coeluted proteins. Blepharismin-rich material with a molecular mass of approximately 50 kDa, consisting of at least nine proteins was obtained when the same extract underwent preparative isoelectric focusing before column chromatography separation. Purification of the pigment obtained from light-exposed cells gave blepharismin-rich material with a molecular weight of approximately 200 kDa. Comparison of the materials obtained under the same conditions, either from the dark-kept or light-irradiated cells, by means of pore-gradient electrophoresis confirmed that proteins present in the two preparations were different. It revealed only a very small amount, if any, of proteins in the chromatography fractions with the highest absorbance at 600 nm. Results are discussed on the basis of the hypothesis that a specific blepharismin-binding protein does not exist in the protozoan.

Shared reaction in solid-phase immunoassay for estriol determination.

In the search of factors responsible for the experimental difficulties in developing accurate and sensitive solid-phase immunoassay of steroids, an experimental model has been set up for the study of nonspecific interaction of the steroid analyte with the coating protein. Along with the development of a highly sensitive enzyme-linked, solid-phase immunoassay for estriol measurement, we observed evidence of shared reactions. This property, to our knowledge not previously described for monomeric, low-molecular-weight antigens like estrogens, has been attributed to the presence of bovine serum albumin, which is capable of binding estrogens through hydrophobic interactions. The addition of estriol in solution in large excess did not reach a complete inhibition of the binding, so the possibility was excluded that the antibody simply binds to the adsorbed estrogen. The simplest explanation for the occurrence of the reaction is the hypothesis that a family of antigen determinants arises when the estriol is conjugated to a protein carrier. The corresponding antibodies are revealed only when the estrogen participates to the actual analytical system in the form of a steroid-protein conjugate. In the experiment, the estriol has been recognized as being coupled with one or more amino acid side chains present around its site of covalent linkage to the immunogen protein. The discussed results may be of help in developing a solid-phase immunoassay of small antigens as steroids, but also in applying the hybridoma and phage display technologies, the screening methods of which are based on sensitized solid phases.

[Hygiene and health importance of histamine as an unhealthy factor in several food products]. / Interesse igienico-sanitario per l'istamina come fattore di insalubrita' di alcuni alimenti.

Epidemiologic reports on food-borne diseases from different countries show not infrequently outbreaks due to histamine toxicity. The Authors were interested in assessing the relative importance of this nosological entity in Italy and made a global review of old and recent literature on the subject referring also their earliest data on a recently performed laboratory work. Several foods can show histamine contents potentially toxic for man; amongst the most frequently incriminated products fish, especially the scombroid species (tuna, mackerel), plays a pre-eminent role in the etiology of the so called scombrotoxic fish poisoning. This syndrome begins from a few minutes to two hours from incriminated meals and presents itself with the characteristic signs and symptoms of histamine activity on various organs and is very rarely, if ever, life threatening. Histamine formation in food is due to the decarboxylase activity of some microorganisms, mainly enterobacteria; they can be part of its normal flora or represent a secondary contamination and find a favourable environment for outgrowth if food is not stored or processed in proper conditions. An international outlook on the epidemiology of this syndrome is then given, including some considerations on the real dimension of the problem in Italy, at present widely underestimated. Though a pioneer work was accomplished by Pergola, who started his researches in 1910 after receiving several reports of food poisoning related to consumption of tuna and finally established the causative role of histamine, we are lacking at present an up to date picture of this problem in our country, notwithstanding a few sporadic notifications. Two of the most relevant ones concern a survey in Rome on a collection of 110 cases observed in the seventies and an outbreak occurred in Palermo in 1979 affecting nearly 250 people. The relationship between the intake of histamine and the clinical effects on man of a given dose are then evaluated together with histamine catabolic pathways in the gut, where possible interference by enhancing substances may occur. Finally a brief review of the analytical methods currently employed gives the Authors the possibility to refer about their first data of a survey on the hygienic quality of scombroid species commercialized in their metropolitan area.