The stability of a complex social system

Analyzing communication data within a social structure represented by a wholesale agricultural market demonstrates the utility of network analysis techniques for identifying systems. A representation of these data in matrix form permits exploration of the stability properties of the system. The stability analyses lend some support for theoretical arguments pertaining to the conditions leading to system equilibrium.     

Somatic variation in micropropagated clones ofCichorium intybus

Summary An experiment aiming to establish whether temporary or persistet somatic variation can arise in clones obtained in vitro by micropropagation has been performed onCichorium intybus. The results point out that persistent modifications of the phenotype can be observed after six cycles of cloning and that when the length of the cloning period is varied these appear to be differential responses of the same genotype to the micropropagation.     

Involvement of prolyl endopeptidase in ascidian fertilization

Inhibitory effects on fertilization of the ascidian of three benzyloxycarbonyl(Z)-aminoacyl prolinals and Z-Gly-Pro-chloromethyl ketone added before and after insemination were examined. The results suggest that the prolyl endopeptidase is involved in the process of fertilization, especially in a process taking place between chorion elevation and cell cleavage.     

A combination of a particular HLA-DP beta allele and an HLA-DQ heterodimer confers susceptibility to coeliac disease

Coeliac disease is an autoimmune disease of the intestinal mucosa, elicited by ingestion of wheat gluten in genetically susceptible individuals. Susceptibility to coeliac disease has been associated with the serologically defined variants DR3 and DR7 of the class II antigens encoded by the HLA-D region. Three related class II antigens, each consisting of an alpha and a beta glycoprotein chain, have been identified and are designated HLA-DR, HLA-DQ, and HLA-DP. These highly polymorphic transmembrane proteins bind peptides derived from the processing of foreign antigens and present them to T lymphocytes; they also influence the specificity of the mature T-cell repertoire. The role of HLA-DP polymorphism in susceptibility has not been as fully explored as that of the other class II antigens because of the complexity of the primed lymphocyte typing (PLT) method for determining DPw specificities. Here we use a new DNA-based method of HLA-DP typing to analyse the distribution of DP beta alleles in a group of coeliac disease patients and healthy controls. Two specific DP beta alleles (DPB4.2 and DPB3) are increased in the patient population. Comparison of the DP beta sequences suggests that the polymorphic residues at position 69 and at 56 and 57 may be critical in conferring susceptibility. Further, the contribution of the susceptible DP beta alleles appears to be independent of linkage to the previously reported DR3 and DR7 markers for coeliac disease. The distribution of DQ alpha and beta alleles in patients suggests that a specific DQ heterodimer may be responsible for the observed DR associations. Individuals with both this DQ antigen and a specific DP beta allele are at increased risk for coeliac disease.     

Peptidylarginine deiminase in rat and mouse hemopoietic cells

Summary Peptidylarginine (protein-L-arginine) deiminase activities have been demonstrated in extracts of rat and mouse peritoneal macrophages, bone marrow cells, splenic adherent cells, neutrophils, and mouse monocyte/macrophage cell lines. The enzyme in these cells is indistinguishable from the skeletal muscle enzyme with respect to immunochemical properties.     

Canavanine in alfalfa (Medicago sativa)

Summary Canavanine was extracted and characterized from various cultivars of alfalfa seed. Values obtained range from 8 g/kg for the Buffalo variety to 14–20 g/kg for the highly weevil resistant variety, Weevl-Chek.     

Releasable GABA in tubular epithelium of rat kidney

Summary The distribution of gamma-aminobutyric acid (GABA) in the rat kidney was examined by immunocytochemical techniques. GABA-like immunoreactivity (GABA-LI) was predominantly confined to the renal tubules, including the ascending parts of the distal tubules, and the loops of Henle, the collecting tubules and ducts, and the connective parts of the convoluted tubules. In GABA-positive cortical tubules, about half of the epithelial cells were labelled. The labelled cell type showed the ultrastructural features of principal cells. Depolarizing stimulation by ouabain and high K⁺ concentration evoked the efflux of endogenous GABA from kidney slices. The present findings, along with previous results, suggest that GABA released from renal tubular epithelium, and transported with the urine, might be involved in the modulation of contractility in the urinary tract.     

Iron acquisition and virulence in the motile aeromonads: siderophore-dependent and -independent systems

During an infection, a microbial pathogen must acquire all of its iron from the host. Aeromonas isolated producing the siderophore amonabactin obtain iron either from host Fe-transferrin (siderophore dependent) or from host heme-containing molecules (siderophore independent). Isolates producing the siderophore enterobactin do not utilize Fe-transferrin in serum and probably rely exclusively on host heme iron.