Controls on fracture openness and reactivation in Forsmark, Sweden.

In crystalline bedrock, the open fraction of the fracture network constitutes the main pathways for fluids. Many observations point out that the state of stress influences the open fraction, likely indicating recent reactivation. But how this occurs is still unresolved. We analyse the conditions for fracture reactivation from fracture data collected in the uppermost 1 km of bedrock in Forsmark, Sweden. The open fraction is mainly correlated to the stress acting normally on the fracture but even away from critical failure, leading us to analyse the potential fluid pressure required for reactivation, [Formula: see text]. We observe that 100% of the fractures are open when [Formula: see text] is hydrostatic, and the ratio decreases exponentially to a plateau of ~ 17% when [Formula: see text] is lithostatic and above. Exceptions are the oldest fractures, having a low open fraction independent of [Formula: see text]. We suggest that these results reflect past pressure build-ups, potentially related to recent glaciations, and developing only if the preexisting open fraction is large enough.

Stereoselective preparation and reactions of configurationally defined dialkylzinc compounds

The reaction of cyclic and open-chain diastereomerically pure secondary organoboranes with diisopropylzinc allows the preparation of secondary dialkylzinc reagents with good to excellent retention of configuration as shown by deuterolysis and CuI- and Pd0-mediated reactions with electrophiles. The importance of a high boron-zinc exchange rate to obtain high diastereoselectivity has been shown. Improvement of the configurational stability and stereomeric purity of the zinc intermediates has been obtained by using mono-isopinocampheylborane ((-)-IpcBH2) providing optically active dialkylzinc compounds (up to 96% ee) with enhanced diastereoselectivities.

Lymphoid leukosis viruses, their recognition as 'persistent' viruses and comparisons with certain other retroviruses of veterinary importance.

Diseases caused by lymphoid leukosis virus (LLV), a retrovirus, take a long time after infection to develop and have a wide variety of pathological manifestations. This long latent period is characteristic of 'persistent virus infections'. Disease produced by LLV infection and its underlying mechanisms is compared with 'persistent' infections caused by other retroviruses in birds and mammals of veterinary importance. The diseases considered for comparison are those caused by reticuloendotheliosis, feline leukaemia, bovine leukosis and equine infectious anaemia viruses. There are significant changes in the immunological status in all diseases caused by these viruses. LLV infections follow this trend with, in manifestations of neoplastic disease, a perturbation of the normal switch that occurs from IgM to IgG synthesis. There are also indications of other immunological disturbances. Factors other than immunological disturbances may contribute to the length of time after infection required for the many forms of LLV infection to appear. Such additional factors may include the operation of 'biological clocks', such as the arrival of sexual maturity, and also the very nature of retroviruses. These factors, like the immunological changes, play major roles in the maintenance and progression of persistent retrovirus infections.

Reflections on scrapie and related disorders, with consideration of the possibility of a viral aetiology.

The transmissible spongiform encephalopathies of domesticated animals, scrapie in sheep and bovine spongiform encephalopathy (BSE), and transmissible mink encephalopathy are more than a scientific curiosity; under certain circumstances their impact on commercial activities can be calamitous. Knowledge of their causation and pathogenesis is still rudimentary, but many consider than an unconventional agent, the prion (a brain protein, PrP), that is not associated with nucleic acid is involved in both. Others believe that conventional viruses, which replicate by virtue of their nucleic acid-defined genes, are involved in the causation and progression of the encephalopathies but that technical problems have prevented their identification. Others postulate even more exotic causative agents. While this paper will particularly address the possibility of a viral aetiology for these diseases, it is also emphasized that our knowledge of the state of the immune system in animals with encephalopathy needs broadening. There are remarkable gaps in our knowledge of the histopathology of these diseases, particularly the nature of the characteristic vacuoles. Much further work is needed on the biochemical changes in the brain and the serum, particularly of the latter as it could lead to an additional means of recognizing clinical cases without waiting for the animal to die with subsequent examination of the brain for characteristic lesions and the presence of protease-K-resistant PrP.

Reflections on viruses and cancer.

In recent years human and animal cancers have increasingly been shown to have a viral component in their aetiology. Oncogenic viruses will continue to be discovered although with certain cancers there is also an important environmental component, and with others--congenital cancers and cancers of early childhood--an important genetic component. There is thus the probability that 'cancer' may not be an entity. Rather it may be a syndrome, the phenotypic expression of alteration of cellular metabolism, differentiation and cell death. More information is needed on the mathematics of cell division and destruction, in vivo and in vitro, and the involvement of 'biological clocks', i.e. ageing processes. These data, when available, should help us to understand better the nature of cancer and lead us to more effective methods of prevention and cure.

Reflections on the pathogenesis of diseases caused by the acute avian leukosis/sarcoma viruses with special reference to avian erythroblastosis.

The various diseases that follow experimental infection with the acute and non-acute avian oncoviruses are discussed with special reference to the pathogenesis of avian erythroblastosis. One view, based on in vitro studies, sees erythroblastosis as the product of a failure in the differentiation of virus-infected stem cells to mature erythrocytes, as a result of cell 'transformation'. The results of some in vivo studies, however, point to a resemblance of the disease to a haemolytic anaemia, where cellular death is an important component. It seems probable that the disease is the result of transformation of cells of the erythroblastic series followed by the death of many of these cells due to influences that have not yet been determined. Determination of the causes of this cellular death may prove to be as important for our understanding of the problem of leukaemia as the work that has already been accomplished in explaining the causes of cell transformation. It is also suggested that the tendency of gs amino acid sequences of the avian leukosis viruses and mouse leukaemia viruses to form fusion proteins with a variety of proto-oncogenes may be part of a wider phenomenon, and that these sequences may fuse with other proteins, altering their properties. More work is required on the possibility that there is an undiscovered immunological component in the progression of the L/S diseases.

Pronase does not reduce the protein content of Hirt supernatant of normal mouse brain.

Normal mouse brain has been used as a model in experiments to explain the reduction of infectivity obtained following incubation with Pronase of brain infected with the scrapie infective agent. Incubation of Hirt supernatants of normal mouse brain with Pronase had no effect on the protein content when compared to controls similarly incubated without Pronase. This points to a resistance of the proteins in the brain extract to protease or to the presence of anti-protease activity. Much of the 'RNA' and 'DNA' detected in the Hirt supernatant by the colorimetric procedures for these nucleic acids was alcohol soluble. The nature of the alcohol-soluble 'nucleic acid' in mouse brain and the resistance of the proteins present in Hirt supernatants to Pronase require further investigation. In experiments where Pronase reduced the infectivity of brain preparations containing the scrapie agent, the effect is probably not due to protease activity; another activity of Pronase must be involved.

ELISA for bovine herpesvirus 1 (BHV1) antibody with HIRT supernatant.

Detailed studies were made of the ability of HIRT supernatant (HS) from bovine herpesvirus 1 (BHV1) infected cultures to sensitize plates for enzyme-linked immunosorbent assay (ELISA). The ultracentrifuged pellet of HS had less sensitizing activity than the supernatant, but the antigen was removed completely by 0.22 micron filters and to some extent by 0.45 micron filters; it was minimally affected by sonication; it was destroyed by the action of Pronase but not by DNAase I when a kallikrein inactivator was added and the mixture incubated; incubation with DNAase II had no effect. Thus the presence of DNA was not required for the sensitizing activity of HS and the antigens recognized by antibodies in HS in ELISA were directed to its protein component. Strong reactions were given in immunoblotting of HS from BHV1 infected tissue cultures with anti-BHV1 glycoprotein monoclonal IgG, but HS from uninfected tissue cultures did not react with the same monoclonal IgG.

Immunoblotting with polyclonal and monoclonal antibody to avian myeloblastosis protein p27: studies of liver proteins in chickens with erythroblastosis.

An antigen detected by complement fixation with polyclonal antibody to avian myeloblastosis virus (AMV) antigen p27, appears in the livers of chickens inoculated with avian erythroblastosis virus (AEV). It can be demonstrated at the 30,000 dalton (30K) molecular weight level by Western immunoblotting of electropherograms of AEV infected liver extracts. The 30K protein reacted strongly with this polyclonal antibody but only weakly with a monoclonal antibody to the same viral antigen and possible explanations for this have been suggested. Both antibodies also appeared to react with other than viral components in the preparations of AMV used. As this apparent non-specific attachment of highly specific antibody may have as its explanation the failure of the gelatin to prevent nonimmunologically determined binding of the immunoglobulin; other blocking agents should be investigated.

On the heterogeneity of serum albumin: effect of sodium dodecyl sulphate on agarose chromatography of the protein.

The chromatographic behaviour of serum albumin changes if it is dissolved in an aqueous solution of sodium dodecyl sulphate (SDS) and is left at room temperature or is heated. Instead of emerging as one peak from an agarose column it emerges as more than one peak and the protein in each when rechromatographed elutes in more than one peak. Electropherograms made in the presence of SDS of the protein in these peaks show multiple banding from proteins migrating with a wide range of molecular weights. The chromatographic and electrophoretic behaviour of serum albumin in the presence of SDS suggests that the protein is not a simple monomer and alternative explanations for this behaviour are discussed.

Further evidence for the heterogeneity of serum albumin.

Albumin samples from three species (avian, bovine and human) were electrophoresed on gradient polyacrylamide gels in the presence of sodium dodecyl sulphate (SDS-PAGE). The resulting electrophoregram from each sample of serum albumin investigated showed multiple protein bands of a wide range of molecular weights. All seven samples of human serum albumin were found, using gel immunodiffusion, to be contaminated with other proteins. All but one sample was contaminated with proteins such as haptoglobin, alpha 1-glycoprotein, alpha 1-trypsin inhibitor, and prealbumin. This contamination accounts for part of the heterogeneity of these samples. Immunoblots, where the proteins were transferred to nitrocellulose and incubated with antisera, gave a better demonstration of the heterogeneity than Coomassie Blue staining and the immunoblotting procedure appeared to be more sensitive than the gel immunodiffusion technique. The heterogeneity of serum albumin demonstrated by the former technique included that of the monomer which was shown to be contaminated with antithrombin III. The commercial samples of human serum albumin, claimed as pure, were found to vary greatly in their tryptophan content, which also indicated heterogeneity. Heat treatment of human serum albumin with 1% SDS, followed by chromatography on agarose, removed the protein contaminants and with it the tryptophan. The presence of tryptophan in human serum albumin, therefore, indicated the presence of impurities.

Tryptophan content of serum albumin.

Tryptophan content of serum albumin was determined spectrophotometrically. The method used for the determination of tryptophan gave consistent results. Results show that the tryptophan contents of bovine and human serum albumin are significantly different from chicken serum albumin. Bovine and human serum albumins, however, are not significantly different from each other. A large difference in tryptophan content was found between two samples of chicken serum albumin. This suggests that the tryptophan content of serum albumin may not be constant for any given species. For these reasons, tryptophan content should not be used to estimate the molecular weight of serum albumin.