Facilitation of transmitter release by neurotoxins from snake venoms

Toxins C13S1C3 and C13S2C3 from green mamba venom (Dendroaspis angusticeps) acted like dendrotoxin to increase acetylcholine release in response to nerve stimulation in the chick biventer cervicis preparation. Proteins B and E from black mamba venom (Dendroaspis polylepis) had no prejunctional facilitatory activity. All four proteins are trypsin inhibitor homologues. Binding of a prejunctional facilitatory toxin (Polylepis toxin I) to motor nerves was rapid and did not require the presence of Ca2+ or nerve stimulation. Binding was not prevented by protease inhibitors that lacked facilitatory actions. Prejunctional facilitatory toxins also augmented transmitter release in the chick oesophagus and the mouse vas deferens preparations. The effects were rapid in onset and could wane spontaneously. 125I-labelled dendrotoxin bound specifically to rat brain synaptosomes with a KD of about 3 nM. Binding was prevented by native dendrotoxin but not by beta-bungarotoxin or atropine. It is concluded that prejunctional facilitatory toxins affect transmitter release at many types of nerve endings in addition to motor nerve terminals. From consideration of the structures of active and inactive molecules, it is thought that binding of the active toxins may involve several exposed lysine residues.     

Use of dextran and post-primary antibody fixation in immunoperoxidase staining of fresh frozen tissue. Detection of immunoglobulin associated with squamous carcinomas of the head and neck

Use of unfixed fresh frozen tissue sections for immunocytochemical studies reduces the possibility of denaturation of antigenic determinants compared to formalin fixation and paraffin embedding procedures. However, tissue and cellular morphology can be extensively altered in the numerous application and washing steps with frozen tissue sections. We tested a number of buffer solutions and showed that the use of dextran-containing buffers and fixation by glutaraldehyde after primary antibody application preserves tissue morphology. The procedures described here are also applicable to ascertaining the presence of Fc receptors of leukocytes in sections of carcinoma tissues. The buffered dextran washes and post-primary antibody fixation method was used to demonstrate the presence of immunoglobulin associated with squamous carcinoma cells. The immunoglobulin was not removed by washing of tissue sections at 37 degrees C but could be removed by low or high pH buffer washes, suggesting that the immunoglobulin is bound in a specific manner.     

Sequences encoding two trypsin inhibitors occur in strikingly similar genomic environments.

The nucleotide sequences of two approx. 4 kilobase pair segments of the bovine genome are presented. One segment contains a coding region for bovine pancreatic trypsin inhibitor (BPTI) and the other segment contains a coding region for a BPTI homologue. The two 4 kilobase pair sequences are strikingly similar over approx. 3.4 kilobase pairs of their sequence, including putative intron sequences, suggesting that they have evolved from a gene duplication event.     

Nutrient control of brain neurotransmitter synthesis and function

Dietary fluctuations in nutrient availability are factors in the regulation of brain function. Until recently the prevailing view was that brain biochemistry and function were influenced by diet only when biochemical and clinical evidence of nutrient deficiency was present. It is now clear, however, that the brain is sensitive and responsive to diet composition. Preliminary data show that variation in vitamin and mineral nutrient intakes over ranges that are considered to maintain normal nutritional status may impact on brain biochemistry, owing to their many coenzyme roles. Furthermore, the synthesis of at least five brain neurotransmitters, namely serotonin, the catecholamines, acetylcholine, histamine, and glycine responds to dietary fluctuations in availability of their nutrient precursors, tryptophan, tyrosine, choline, histidine, and threonine, respectively. Not only are these biochemical events altered by normal variations in diet composition, but considerable evidence now exists to show that the brain uses this information to regulate many functions. Future studies can be expected to continue to elucidate the links between diet, brain neurotransmission, and brain function, and to exploit the application of these links in understanding the function of the brain under normal and disease conditions.     

Glucose metabolism of embryos and endosperms from deteriorating barley and wheat seeds

Changes in glucose utilization into CO₂ and ethanol-insoluble material were followed in whole seeds, embryos, and endosperms of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) which had reached different levels of deterioration through accelerated aging treatments. Excised embryos from deteriorated wheat seeds had reduced respiration and glucose utilization into ethanol-insoluble material but not into CO₂. These treatments had no effect on respiration of excised endosperms, although they reduced utilization of glucose into ethanol-insoluble material and CO₂. Changes in metabolic activity of whole seeds in response to deterioration treatments are difficult to interpret because they represent the sum of the changes that take place in the embryos and endosperms. Changes in respiration and glucose utilization in these two tissues neither proceed at the same rate nor go in the same direction during deterioration.     

Comparative enzymology of the adenosine triphosphate sulphurylases from leaf tissue of selenium-accumulator and non-accumulator plants

1. ATP sulphurylases were partially purified (20-40-fold) from leaf tissue of Astragalus bisulcatus, Astragalus racemosus (selenium-accumulator species) and Astragalus hamosus and Astragalus sinicus (non-accumulator species). Activity was measured by sulphate-dependent PP(i)-ATP exchange. The enzymes were separated from pyrophosphatase and adenosine triphosphatase activities. The properties of the Astragalus ATP sulphurylases were similar to the spinach enzyme. 2. The ATP sulphurylases from both selenium-accumulator and non-accumulator species catalysed selenate-dependent PP(i)-ATP exchange; selenate competed with sulphate. The ratio of V(selenate)/V(sulphate) and K(m)(selenate)/K(m)(sulphate) was approximately the same for the enzyme from each species. 3. Sulphate-dependent PP(i)-ATP exchange was inhibited by ADP, chlorate and nitrate. The kinetics of the inhibition for each enzyme were consistent with an ordered reaction mechanism, in which ATP is the first substrate to react with the enzyme and PP(i) is the first product released. 4. Synthesis of adenosine 5'-[(35)S]sulphatophosphate from [(35)S]sulphate was demonstrated by coupling the Astragalus ATP sulphurylases with Mg(2+)-dependent pyrophosphatase; the reaction was inhibited by selenate. An analogous reaction using [(75)Se]selenate as substrate could not be demonstrated.     

Grey seals, Halichoerus grypus, of the Dee Estuary and observations on a characteristic skin lesion in British seals

Grey seals on the West Hoyle Bank feed on a variety of fish and have a high incidence of dermal lesions, often associated with emaciation and nematode parasite infection. Corynebacterium phocae has been isolated from an active lesion. The significance of large numbers of seals in the Dee Estuary bearing lesions is discussed and the occurrence of seals with lesions elsewhere in British waters is reviewed. No evidence was found to associate the dermal lesions with any environmental factor and it is probable that lesions develop as a result of infection of minor wounds.