Bibliothek

Notizen: The relation between substitutional symmetry operations that leave a real symmetric matrix invariant and the degeneracies exhibited by the matrix in diagonal form are examined. The usual application of group theory to this problem is formulated. Substitutional (and other) symmetries can exist, which do not form part of the invariance group. These symmetries can cause extra degeneracy of the root system and are frequently encountered in some physical applications such as the Hückel model of molecular bonds. Some general features that lead to extra degeneracy are noted and illustrative examples are given for systems of six equivalent centers.

Notizen: In atomic or nuclear shell theory the quadratic Casimir operators can be used to evaluate the expectation values of two-body interactions among equivalent members of a shell. Racah has given closed expressions for these Casimir operators for all the groups in the Racah chain. In this paper an alternate derivation of these closed expressions based on duality with the symmetric group is given. The derivation allows extension of these expressions to situations in which equivalent spins are in an environment, such as a point group, for which the two-body interactions separate into distinct sets. Possible application to NMR systems with spin ≥1/2 are discussed.

Notizen: The method uses an autoanalyzer continuous flow reaction system to oxidize toxin in standard acid extracts of shellfish, prepared for mouse bioassay, to derivatives which are detected by fluorescence. Oxidation is by periodic acid under alkaline (NH4OH) conditions and is followed by acidification by acetic acid. Concentrations of 10 μg/100g toxin and above can be measured with good reproducibility and accuracy: coefficient of variation was 9.5% for samples with 60 μg/100g or greater. Correlation with the mouse bioassay was 0.82 for 204 samples (toxin from 0–2000 μg/100g). The method is proposed to screen shellfish samples for PSP toxins with only samples falling into the range 60–250 μg/100g being subject to the more tedious and expensive mouse bioassay.

Notizen: Four cases illustrating aspects of multiple keratoacanthoma syndromes are reported. One patient with the classical picture of the familial Ferguson Smith variety provided an additional example of an affected family from Glasgow where the majority of the early cases were studied. The second patient displayed striking susceptibility to the effect of minor trauma in provoking new tumours and provided a unique model for the observation of the development of Keratoacanthoma. The third patient demonstrated complete disappearance of tumours during an episode of exfoliative dermatitis. The fourth patient provided an example of the interaction of nodular neurodermatitis and multiple keratoacanthomas.

Notizen: A high incidence of keratoacanthoma was found in south east Queensland, and attributed to the influence of sunlight in a sub-tropical climate. The proportion of lesions on the upper and lower limbs was higher than that found among the population of colder climates. Renal transplant patients produced increased numbers of keratoacanthomas, and one patient died from a metastasizing invasive keratoacanthomas-like lesion. An exenteration of the orbit became necessary in a patient treated for keratoacanthoma adjacent to the eyelid.The concept of keratoacanthoma, the relationship to squamous cell carcinoma, the method of regression and immunological aspects are reviewed.

Notizen: Abstract Toxin content (fmol cell−1) and a suite of elemental and macromolecular variables were measured in batch cultures of the dinoflagellatesAlexandrium fundyense, A. tamarense andAlexandrium sp. from the southern New England region, USA. A different perspective was provided by semicontinuous cultures which revealed sustained, steady-state physiological adaptations by cells to N and P limitation. Two types of variability were investigated. In batch culture, changes in nutrient availability with time caused growth stage variability in toxin content, which often peaked in mid-exponential growth. A second type of variability that could be superimposed on growth stage differences is best exemplified by the high toxin content of cells grown at suboptimal temperatures. Calculations of the net rate of toxin production (R tox ; fmol cell−1 d−1) for these different culture treatments and modes made it possible to separate the dynamics of toxin production from cell division. Over a wide range of growth rates, cells produced toxin at rates approximating those needed to replace “losses” to daughter cells during division. The exception to this direct proportionality was with P limitation, which was associated with a dramatic increase in the rate of toxin production as cells stopped dividing due to nutrient limitation in batch culture. Growth stage variability in batch culture thus reflects small imbalances (generally within a factor of two) between the specific rates of toxin production and cell division. N limitation and CO2 depletion both affect pathways involved in toxin synthesis before those needed for cell division; P limitation does the opposite. The patterns of toxin accumulation were the same as for major cellular metabolites or elemental pools. The highest rates of toxin production appear to result from an increased availability of arginine (Arg) within the cell, due to either a lack of competition for this amino acid from pathways involved in cell division or to increased de novo synthesis. There were no significant changes in toxin content with either acclimated growth at elevated salinity, or with short term increases or decreases of salinity. These results demonstrate that toxin production is a complex process which, under some conditions, is closely coupled to growth rate; under other conditions, these processes are completely uncoupled. Explanations for the observed variability probably relate to pool sizes of important metabolites and to the differential response of key biochemical reactions to these pool sizes and to environmental conditions.

Notizen: Abstract Procedures have been developed for the extraction and high-performance liquid chromatography (HPLC) analysis of paralytic shellfish poisoning (PSP) toxins from Protogonyaulax spp. grown in batch culture. Using these procedures, the toxin content of two isolates of P. tamarensis (NEPCC 183 and 255) and one isolate of P. catenella (NEPCC 355) were examined. Total toxin and individual toxin concentrations were measured for each isolate during the exponential and stationary phases of growth in batch culture. The total toxicity of each isolate as measured by HPLC analysis was found to agree with toxicity as determined by the standard mouse bioassay. Two of the isolates (255 and 355) were found to be toxic and the third (183) was non-toxic. The toxic isolates (255 and 355) both showed higher average total PSP toxin content during the exponential phase (35 and 23 fmol toxin cell-1, respectively) than during the stationary phase (21 and 8 fmol toxin cell-1, respectively). These cultures differed dramatically in their toxin composition. P. tamarensis (255) contained a large proportion of the N(21) sulfo toxins (B1, B2, C1, C2) while P. catenella (355) contained primarily Gonyautoxins 1 through 4. The percent composition of individual toxins was found to be constant throughout the growth cycle for both toxic isolates, even though the total toxin concentration varied. Our results suggest that PSP toxin profiles might be useful as chemotaxonomic indicators.

Notizen: Abstract Toxin production was measured by high pressure liquid chromatography (HPLC) when the marine dinoflagellate Protogonyaulax tamarensis (NEPCC 255) was grown under nitrogen or phosphorus limitation. The major toxins found in P. tamarensis (255) consisted of (N21-SO 3 - )STX (11%), (N21-SO 3 - )NeoSTX (44%), and [(N21-SO 3 - )GTX2 plus (N21-SO 3 - )GTX3] (20%). Total toxin content on a per cell basis was high for cultures in log phase (30 to 40 fmol cell-1) and then decreased to ca 20 fmol cell-1 as the cultures entered stationary phase. There was a gradual decrease in the toxin content per cell during nitrogen-limited stationary phase to ca 3 fmol cell-1 or less. Phosphorus-limited cultures showed a markedly different response than nitrogen-limited cultures. Toxin content in P-limited cells dramatically increased at the start of stationary phase, reaching levels 3 to 4 times that observed in control and nitrogen-limited cultures. These results cannot be explained by changes in the average cell volume. Eventhough dramatic effects on the total toxin concentration were observed in response to nutrient limitation (N or P), the toxin composition (on a percent basis) remained constant. This suggests that the individual toxin composition of a given isolate is a fixed genetic trait and not a transient response to changing environmental factors.