Comparative properties of ferredoxins from a marine and freshwater species of Porphyridium

Ferredoxins were isolated from the freshwater red alga Porphyridium aerugineut, and from Porphyridium cruentum, a related marine species. A sin     

A neutral model of community organization

A discrete time simulation model is described which is neutral (sensuCaswell, 1976) with respect to competition-based community organizational hypotheses. The model randomly locates rectangular niches (identified with species) in a two-dimensional resource hyperspace. Populations for each niche are randomly assigned and increase or decrease randomly in the absence of predation. Predation is represented by a “Lnegative niche” (viz., a rectangular region in the two-space) which removes all organisms that lie within it (i.e. reduces the populations in niches that overlap it in proportion to the overlap). Competition is not represented; hence, the model is neutral with respect to hypotheses of the role of competition in organizing communities.The model determines a number of measures of community organization at each time step: average niche size, average overlap between niches, species diversity, number of niches, average population size, average number of neighbors. Statitistical analyses allow comparison of results between runs and with field data.Model behavior is explained by deriving dimensionless variables that relate model parameters to output. These variables were derived using one set of simulations. A second set of simulations is used to validate the relationships. These relationships are interpreted as testable hypotheses of community organization that do not depend on competition. Preliminary tests are given by comparing qualitatively model output with data from lizard and small mammal communities.     

Hospital work load produced by breast-cancer screening programme run by trained non-medical staff.

In a feasibility study of mass population screening for breast cancer by annual clinical examination and mammography the findings of non-medical staff (nurses and radiographers) were used to estimate the hospital work load generated by such a programme. Among 2490 women who attended for the first time by invitation the rate of referral for a surgical opinion based on the findings of the non-medical staff was 7.9% and the biopsy rate 2.5%. In the second and third years referral rates fell to 4.3% and 2.7% respectively and the biopsy rates to 1.1% and 1.4%. The rates of referral and biopsy among 1203 women who referred themselves for screening were higher, but many self-referred women were symptomatic; those without symptoms had rates of referral and biopsy similar to those of the invited women. Extrapolation of these findings to a population of 200,000 in a typical health district showed that the hospital work load would be high in the first year of screening with 44 outpatient referrals per week and 14 biopsies. By the third year, however, only seven referrals and four biopsies a week could be expected. The work load would be reduced by a third if screening were confined to women over the age of 50.     

Fast atom bombardment: A new mass spectrometric method for peptide sequence analysis

We have studied a selection of peptides using a new mass spectrometric ionisation technique - fast atom bombardment (FAB). We define the fragmentation pathways observed and comment on the utility in sequence analysis. A simple acetylation experiment is shown to aid rapid sequence assignment.     

Cytochalasin B blocks sperm incorporation but allows activation of the sea urchin egg

Cytochalasin B (CB) (2 × 10⁻⁶ M) prevents the incorporation of sperm into the eggs of Lytechinus pictus and Strongylocentrotus purpuratus as judged by light and transmission electron microscopy (TEM). At lower concentrations of CB (2 × 10⁻⁷ M), sperm are successfully incorporated into the egg, but their migration in the area of the egg cortex is impaired. The site of action of CB on the sperm may be on the initial rotation of the sperm nucleus in the cortex; the subsequent migration is not affected by CB. Although sperm incorporation is prevented at the higher CB concentrations, the eggs become activated—as judged by cortical reaction, increased protein synthesis and increased respiration. These findings raise the concept that egg activation by sperm could result from some pre-fusion event and hence that sperm-egg fusion would not be a prerequisite for the triggering of development. An alternative hypothesis is that fusion occurs between the acrosome process membrane and egg membrane, but since CB has destroyed the integrity of the cortex actin, the fusion bridge is so weak that it cannot be maintained without some contractile or cytoskeletal support by the cortex. The sperm may activate the CB-treated egg in the same manner as pricking with a microelectrode sometimes does.     

Detergent induced inhibition of eukaryotic RNA polymerase B activity and amanitin binding

We studied the effect of detergents on the binding of amanitin to RNA polymerase and on enzymatic activity. SDoS, Sarkosyl and deoxycholate were most inhibitory. Cholate and non-ionic detergents were less inhibitory. Evidence is presented that Sarkosyl inhibits chain elongation. The inhibition of amanitin binding was most influenced by the hydrophilicity of the detergent.     

Thirteen new chromosome-7 congenic lines

Thirteen new congenic lines have been produced which have chromosome-7 segments introduced from different strains onto the C57BL/10Sn background. Sublines B10.P(61NX)C,D, and E received chromosome-7 segments from P/J, B10.CE(62NX) from CE/J, B10.SEC(64NX)A,C,E, and F from SEC/1Re, B10.SM(65NX) from SM/J, B10.WB(66NX) from WB/Re, B10.A(67NX) from A/SnGrf, B10.AKR(68NX) from AKR/SnGrf, and B10.K(69NX) from C3H.K. Isograft testing indicated that three sublines, B10.P(61NX)D, B10.CE(62NX)B, and B10.WB(66NX)B are histoisogenic, i.e., histocompatible within each line. With the exception of B10.A(67NX), B10.AK(68NX), and B10.K(69NX), which have not been isografted, the remaining sublines showed residual heterozygosity on isografting. The three histoisogenic lines have undergone F₁ testing and have been found to possess theH-4 ^a allele and new and distinct alleles at theH-1 locus. They have been designated B10.P(61NX)-H-4^a H-1 ^d , B10.WB(66NX)-H-4^a H-1 ^e , and B10.CE(62NX)-H-4^a H-1 ^f . Direct exchange of grafts has indicated the following genotypes: B10.A(67NX)-H-4^a H-1 ^b , B10.AK(68NX)-H-4^a H-1 ^b , and B10.K(69NX)-F-4^a H-1 ^b . The B10.SEC(64NX) and B10.SM(65NX) sublines have not been typed completely forH-4 andH-1. F ₁ testing or direct exchange of skin grafts indicated that B10.P(61NX)-H-4^a H-1 ^d , B10.WB(66NX)-H-4^a H-1 ^e , B10.A(67NX)-H-4^a H-1 ^b B10.AK(68NX)-H-4^a H-1 ^b and B10.K(69NX)-H-4^a H1 ^b possess nonon-H-1 histocompatibility differences from the G57BL/10 background.     

Accuracy of diagnostic content of hospital activity analysis in infectious diseases.

Hospital activity analysis (HAA) was used to identify 2151 patients in whom the diagnostic code fell within the infectious disease categories of the International Classification of Disease. The clinical notes of these patients were examined by a doctor and in 414 (19.2%) the diagnostic coding was incorrect. Diarrhoea and viral infections were miscoded most often. The possibility of inaccuracy must be considered when HAA aggregated data are used for planning purposes. Accuracy could be improved if clinicians routinely completed the diagnostic sections of the HAA form.