Comparative structural and immunochemical properties of leghaemoglobins

Circular dichroism studies on leghaemoglobins from snake bean, lupin, serradella and other plants show that, in common with soybean (reported earlier) they have a similar overall polypeptide chain conformation and haem environment and orientation. Immunochemical studies, on the other hand, suggest that the antigenic determinants on the surface of the leghaemoglobins vary considerably. Thus, firstly the alpha-helix content of the leghaemoglobins as a class is very similar (60-65%) and approaches that of the myoglobins, secondly, the sign, magnitude and shape of their circular dichroism spectra in the near ultraviolet, Soret and visible regions suggest close similarities in the environment and orientation of a structurally important tryptophan residue and of the haem moiety, and thirdly, there is comparatively weak haem-protein interaction. The extent of immuno cross-reactivity was found to be best deomonstrated using the Farr radioimmunoassay procedure. The results were (a) 5 leghaemoglobins from one plant (soybean) crossreacted completely but with varying affinities. (b) The extent of cross reactivity between leghaemoglobins from different plants was compared to that within a single plant; the reaction of antiserum to a soybean leghaemoglobin with a serradella leghaemoglobin was weak, with a snake bean leghaemoglobin still weaker (and incomplete) while lupin leghaemoglobins showed no cross reactivity at all. (c) The "rapid" attenuation of cross reactivity among different plant leghaemoglobins is explicable in terms of the extensive amino acid substitutions which have been demonstrated in the literature and in the present studies. (d) In view of this rapid divergence it is not surprising that sperm whale and horse heart myoglobins showed no cross reactivity with soybean leghaemoglobins. In summary, amino acid substitutions in the leghaemoglobin family are conformationally but not immunochemically conservative.     

Cerebral ischemic events associated with prolapsing mitral valve

Twelve patients who had no evidence of arteriosclerotic cerebral vascular disease, lacked hypertension or coagulation defect, and had not been receiving contraceptive therapy had recurrent transient cerebral ischemic attacks (TIAs) and partial nonprogressive strokes. All had prolapsing mitral valve proved by angiocardiography. The average age was 38 years, compared with 62 years in a larger series of patients with TIA associated with arteriosclerosis. We propose that the ischemic events are related to emboli emanating from the abnormal mitral valve with or without an associated paroxysmal cardiac arrhythmia.     

Effective use of nisin to control Bacillus and Clostridium spoilage of a pasteurized mashed potato product

Heat-resistant spore-forming bacteria such as Bacillus and Clostridium can survive and grow in cooked potato products. This situation represents both a public health problem and an economic problem. The natural food preservative nisin is used in heat-treated foods to prevent the growth of such bacteria. A cocktail of Clostridium sporogenes and Clostridium tyrobutyricum spores was inoculated into cooked mashed potatoes, which were vacuum packed, pasteurized, and incubated at 8 and 25 degrees C. The shelf life of the mashed potatoes at 25 degrees C was extended by at least 58 days with the addition 6.25 microg of nisin per g. At 8 degrees C, in control samples not containing nisin, the natural contaminant Bacillus grew, but the inoculated Clostridium strains did not until the temperature was raised to 20 degrees C after 39 days. No bacterial growth occurred in nisin-containing samples. The shelf life of the mashed potatoes was extended by at least 30 days with 6.25 microg of nisin per g. In trials involving a cocktail of Bacillus cereus and Bacillus subtilis strains, 6.25 microg of nisin per g extended the shelf life of mashed potato samples that were not vacuum packed by at least 27 days at 8 degrees C. At 25 degrees C, 25 microg of nisin per g extended shelf life by a similar period. Shelf life extension was also observed at lower nisin levels. Microbiological analysis of the mashed potato ingredients showed that a high spore level was associated with the onion powder. It is emphasized that the preservative and the ingredients must be well mixed to ensure good nisin efficacy. Nisin remained at effective levels after pasteurization, and good retention was observed throughout the shelf life of the mashed potatoes.     

A computer model of intracranial dynamics integrated to a full-scale patient simulator

The ability to visualize intracranial dynamics during simulated clinical scenarios is a valuable tool for teaching brain physiology and the consequences of different medical interventions on the brain. Studies have isolated physiologic variables and shown their effects on brain dynamics. However, no studies have shown the combined effects of these variables on intracranial dynamics. This brain model offers one approach that brings all these relationships together and shows how they affect the dynamics of the brain. The brain model obtains its physiologic inputs from a full-scale patient simulator which responds to clinical interventions. This integration allows individuals working on the patient simulator to see the effects of their actions on brain dynamics. The brain model gives a real-time display of intracranial events (cerebral metabolic rate, cerebral blood flow, cerebral blood volume, cerebral perfusion pressure, and intracranial pressure) and responds to changes in the pulmonary and cardiovascular condition of the patient simulator.     

Rupture recurrence after surgical repair of postinfarction ventricular septal rupture. Influence of early thrombolysis

OBJECTIVES: The aim of this study was to identify factors causing rupture recurrence after surgical repair of postinfarction ventricular septal rupture and to evaluate the indication for reoperation. PATIENTS: Recurrence of rupture was analysed in 25 out of a series of 109 patients who underwent surgical repair for postinfarction ventricular septal rupture between 1980 and 1992 in our institution. RESULTS: The mean interval between initial operation and recurrence was 3.6 days with a median of 2 days. Multivariate logistic regression analysis identified early thrombolysis after infarction (P = 0.0085) as a risk factor for recurrence of the rupture. Rupture recurrence occurred more in the anterior then in the posterior infarction site, although non-significant. Reoperation was indicated in 15 patients, in 13 for postrecurrent cardiac failure. The main determinant of cardiac failure was a large postrecurrent shunt (P = 0.05). The mean interval between initial operation and reoperation was 136 days with a median of 101 days. In 6 patients a combined apical ventricular septal rupture recurrence and anterior ventricular aneurysm was found, in 9 patients the recurrent rupture was proximally located, without concomitant aneurysm formation. Of 15 patients who were reoperated, one died in hospital and three after the in-hospital period. Of 10 patients treated conservatively, one died in hospital and two after the in-hospital period. One residual ventricular septal rupture closed spontaneously. CONCLUSIONS: Rupture recurrence is mainly determined by early thrombolysis. Postrecurrent cardiac failure, as the main indication for reoperation, is dependent on postrecurrent shunt size.     

Malondialdehyde and 4-hydroxy-2-nonenal in plant tissue cultures: LC-MS determination of 2,4-dinitrophenylhydrazone derivatives

The cytologically active secondary lipid peroxidation products, malondialdehyde (MDA) and 4-hydroxy-2-nonenal (HNE) have been detected as their 2,4-dinitrophenylhydrazone (DNP) derivatives in plant tissue cultures using LC-MS. This paper reports, for the first time, the use of LC-MS methodology to definitively identify 4-hydroxy-2-nonenal in plants. Limits of detection for the two derivatives are approximately 5 pmol (1.2 x 10(-9) g; 1 microM) and 0.1 pmol (3 x 10(-11) g; 20 nM) respectively. Mass spectrometer response was linear in the range from 2-200 microM DNP-MDA and 0.02-10 microM DNP-HNE. This methodology has been used to assess the formation of aldehydic secondary lipid peroxidation products in dedifferentiated callus cultures of Daucus carota. The finding that profiles of MDA and HNE can be correlated with embryogenic competence is of considerable interest as oxidative status has already been implicated as a regulatory factor in animal development.     

Structural and electrical properties of Na0.47K0.47Li0.06NbO3 lead-free piezoelectric ceramics modified by AgSbO3

(1?x)Na_0.47K_0.47Li_0.06NbO₃ (NKLN)–xAgSbO₃ lead-free piezoelectric ceramics were prepared using a reaction sintering method. The effects of AgSbO₃ doping on the structural and electrical properties of NKLN ceramics sintered at 1000–1040 °C were studied. The dopant affected densification, phase content, sintering temperature, microstructure and electrical properties. Variations in the relative intensity of X-ray diffraction peaks were consistent with Ag⁺ and Sb⁵⁺ ions substituting on the perovskite lattice to produce a change in the proportions of co-existing tetragonal and orthorhombic phases. Grain growth during secondary re-crystallization was also affected. The temperature of the orthorhombic–tetragonal (O–T) phase transition and the Curie temperature (T_C) decreased as a result of AgSbO₃ modifications. The dielectric and piezoelectric properties are enhanced for the composition near the orthorhombic–tetragonal polymorphotropic phase boundary. The 0.92Na_0.47K_0.47Li_0.06NbO₃–0.08AgSbO₃ ceramics exhibited optimum electrical properties (d₃₃=252 pC/N, ε_r=1450, tan δ=0.02, and T_C=280 °C). These results reveal that (1?x)Na_0.47K_0.47Li_0.06NbO₃–xAgSbO₃ ceramics are promising materials for lead-free piezoelectric application.     

The mechanism of the sudden termination of carbon nanotube supergrowth

The effect of growth conditions and catalyst lifetime on the supergrowth of carbon nanotubes (CNTs) through a water assisted chemical vapor deposition has been investigated. The reasons behind the observed sudden termination of the CNT growth were explored. A proper amount of water was found to improve the activity of the catalyst and enhance the growth rate of CNTs. However, the introduction of water did not extend the catalyst lifetime leading to unavoidable termination of the CNT growth. Further experiments demonstrated that in addition to catalyzing the CNT growth, catalyst particles can also decompose/etch the C sp2/sp3 bonds including those in the CNTs. The existing termination mechanism for the CNT growth fails to explain this. We therefore propose a model based on the catalyst phase transformation using the Johnson–Mehl–Avrami–Kolmogorov theory to predict the growth rate and termination of the CNT growth.     

Effect of MnO on the Phase Development, Microstructures, and Dielectric Properties of 0.95Na0.5K0.5NbO3–0.05LiTaO3 Ceramics

Lead-free piezoelectric ceramics in the system 0.95Na_0.5K_0.5NbO₃–0.05LiTaO₃ were modified with ≤1 mol% MnO. Maximum densities occurred at a sintering temperature of 1050°C. Characteristic changes in the relative intensity of X-ray diffraction peaks were consistent with Mn ions substituting on the perovskite lattice to produce a change from orthorhombic to a mixture of tetragonal and orthorhombic phases. Grain growth during secondary recrystallization was also affected, leading to increased grain sizes. The dielectric constant increased from ∼600 in unmodified ceramics to ∼1040 in ceramics prepared with 0.5 mol% MnO.