Biochemical and cytochemical comparison of intestinal bicarbonate-stimulated Mg2+ dependent ATPase and alkaline phosphatase activities in rat, rabbit and guinea pig

Summary Bicarbonate-stimulated Mg²⁺ dependent ATPase activity was demonstrated both biochemically and cytochemically, in brush border membranes from rat, rabbit and guinea pig duodenum. There was no correlation between enzyme activity and basal HCO ₃ ^- secretion rates in the different species. The concentration of HCO ₃ ^- necessary for optimal stimulation of ATPase activity, degree of stimulation and total activity was higher in the rat than in other species. Activity was higher in rat duodenum than in the ileum. This is consistent with the proposed electrogenic HCO ₃ ^- secretion in the duodenum. Distribution of activities of alkaline phosphatase and HCO ₃ ^- -stimulated Mg²⁺-ATPase along the duodenal villus showed significant differences, suggesting that the two activities reflect, at least in part, distinct enzymes.     

Fate of salmonellas and competing flora in meat sample enrichments in buffered peptone water and in Muller-Kauffmann's tetrathionate medium

Studies have been carried out in which growth patterns of a Salmonella sp. and competing micro-organisms, especially other Enterobacteriaceae, were followed during pre-enrichment in buffered peptone water (BPw) and subsequent selective enrichment in tetrathionate broth (TBB). Pre-enrichment cultures were inoculated with minced meat and three reference samples containing nalidixic acid-resistant salmonellas. Irrespective of their initial numbers in BPw, Enterobacteriaceae increased to 10(8)/ml or more. During incubation in TBB at 43 degrees C, numbers of lactose-positive Enterobacteriaceae decreased in most enrichments which resulted in a positive salmonella isolation, but remained constant in the majority of those that did not. Levels of lactose-negative Enterobacteriaceae did not decrease in most salmonella-positive tests, but did so in half of the salmonella-negative ones. In the salmonella-positive tests the numbers of salmonellas had increased to 10(3)-10(7)/ml in BPw and after transfer to TBB slowly reached 10(4)/ml or more. In all cases the numbers of salmonellas exceeded those of the competing flora on brilliant green agar (BGA). In the salmonella-negative tests the numbers of salmonellas had increased less in BPw and decreased in most of the TBB enrichments. In none of these negative tests did the numbers of salmonellas exceed those of the competing flora on BGA. Escherichia coli dominated in most of the salmonella-negative tests. The results suggest more influence of lactose-positive than lactose-negative Enterobacteriaceae on the detection of salmonellas. The effect of competing microorganisms seems to depend not only upon their initial numbers, but also upon the types that can interact with salmonellas during selective enrichment.     

Novel synaptic structures in the central nervous system of the locust Schlstocerca gregaria

Summary An electron-microscopical study of locust thoracic ganglia reveals that synapses in the neuropily are morphologically heterogeneous. In addition to the conventional dyadic type described frequently in the literature, there is a second type with a complex arrangement of presynaptic dense material and a non-dyadic postsynaptic configuration. Serial-section analysis of these synapses suggests that the presynaptic structures include irregular or curved bars, and small projections.Although the proportion of non-dyadic synapses in the neuropile as a whole is small, a substantial number have been found on the branches of an identified flight motor neurone, labelled intracellularly with metal ions in conjunction with silver intensification. Samples from the arborization of this neurone give some indications of the distribution of non-dyadic synapses on it.The results are discussed in the context of distribution of synapses on other identified locust neurones, and the functional morphology of synapses in other phyla.     

Alteration of Extracellular Enzymes in Pinto Bean Leaves upon Exposure to Air Pollutants, Ozone and Sulfur Dioxide

Diamine oxidase and peroxidase, associated with the wall in pinto bean (Phaseolus vulgaris L. var Pinto) leaves, can be washed out by vacuum infiltration and assayed without grinding the leaf. The diamine oxidase activity is inhibited in vivo by exposure of the plants to ozone (dose of 0.6 microliters per liter x hour), whereas the peroxidase activity associated with the wall space is stimulated. This dose does not cause obvious necrosis or chlorosis of the leaf. These alterations are greater when the dose of ozone exposure is given as a triangular pulse (a slow rise to a peak of 0.24 microliters per liter followed by a slow fall) compared to that given as a constant square wave pulse of 0.15 microliters per liter for the same 4 hour period. Exposure of the plants to sulfur dioxide (at a concentration of 0.4 microliters per liter for 4 hours) does not result in any change in the diamine oxidase or peroxidase activities, yet the total sulfhydryl content of the leaf is increased, demonstrating the entry of sulfur dioxide. These two pollutants, with different chemical reactivities, affect the activities of the extracellular enzymes in different manners. In the case of ozone exposure, the inhibition of extracellular diamine oxidase could profoundly alter the movements of polyamines from cell to cell.     

Nodule formation is stimulated by the ethylene inhibitor aminoethoxyvinylglycine

Previous researchers found that formation and function of nitrogen-fixing nodules on legume roots were severely inhibited by addition of exogenous ethylene. Nodule formation by Rhizobium meliloti on Medicago sativa was stimulated twofold when the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) was added with the inoculum. Stimulation of nodule formation by AVG showed a similar concentration dependence as inhibition of ethylene biosynthesis, suggesting that the primary action of AVG is the inhibition of ethylene biosynthesis. When AVG was added 2 to 3 days after inoculation, the number of nodules formed was still increased. On a per plant basis, however, the average nitrogen fixation was unchanged by AVG treatment and was independent of nodule number.     

Sequence-specific 1H-n.m.r. assignments and peptide backbone conformation in rat epidermal growth factor.

The solution conformation of rat epidermal growth factor (EGF) has been investigated by proton n.m.r. techniques. Two-dimensional proton n.m.r. experiments have allowed sequential resonance assignments to be made for most protons. On the basis of these assignments, two regions of anti-parallel beta-sheet structure have been derived from the n.m.r. data. A beta-sheet segment running from about V19 to V23 (capital letters refer to amino acids in the single-letter notation) is folded onto a beta-sheet segment running from R28 to N32 and joined by a chain reversal from E24 to D27. A second region involves a beta-turn from V34 to Y37, which starts a short beta-sheet up to G39, followed by a chain reversal up to Q43, which leads to folding of the C-terminal beta-sheet segment, i.e. H44-R45, running antiparallel to the short Y37 beta-sheet segment. The N-terminal segment up to G18 exists in a multiple bend conformation and is folded on to the V29-V23/R28-N32 beta-sheet such that Y10, Y13, Y22 and Y29 are proximal to each other. Structural comparison of rat, murine and human EGFs indicates a number of highly conserved structural features common to at least these species of EGF.     

High degree of homology between primary structure of human lysosomal acid phosphatase and human prostatic acid phosphatase

Alignment of the amino-acid sequences of the human lysosomal acid phosphatase (LAP) and human prostatic acid phosphatase (PAP) yielded an extensive homology between the two mature polypeptide chains. In the overlapping part, which extends over the entire PAP sequence and the N-terminal 90% of the LAP sequence, the identity is 49.1%. The LAP has an additional C-terminal sequence, which is encoded by the last exon of the LAP gene. This sequence contains the transmembrane domain of LAP, which is lacking in the secretory PAP. All six cysteine residues as well as 20 out of 27 (LAP) and 26 (PAP) proline residues present in the overlapping part of the proteins are conserved, suggesting that they are involved in stabilization of the tertiary structure of both proteins. Only two out of 8 N-glycosylation sites in LAP and 3 in PAP are conserved, suggesting that the dense N-glycosylation of LAP is related to its function in lysosomes.     

Effect of orally-administered epidermal growth factor on intestinal iron absorption and mucosal permeability

A progressive increase in intestinal 59Fe3+ absorption was observed on oral feeding of mice with physiological doses of EGF/UGO. Maximal changes were apparent after 3d and appeared to be dose-dependent. In addition to a small increase in intestinal cell proliferation, as reflected by increased ornithine decarboxylase activity, EGF/UGO-feeding increased mucosal permeability (evaluated with [51Cr]-EDTA): the latter could account for the increase in iron absorption. Sialoadenectomy, to remove the major source of endogenous EGF/UGO, had no appreciable effect on the intestinal absorption of iron.     

Sublethal effects of aldicarb on the behaviour of Aphis fabae and two clones of Myzus persicae and on the transmission of beet mosaic virus by these aphids

In laboratory experiments treatment of sugar-beet plants with aldicarb stimulated the mobility of Aphis fabae and two clones of Myzus persicae which were susceptible (S) and resistant (R) to carbamate-based insecticides, respectively. On the other hand, the number of aphids probing and the total number of probes made was reduced, and hence the transmission of beet mosaic virus (BMV) was restricted. In outdoor experiments the spread of BMV from aldicarb-treated plants by naturally infesting aphids was also restricted. The number of infected plants decreased with increasing distance from the sources of infection.

---

Résumé Des plantes de betterave traitées au laboratoire avec de l'aldicarbe ont stimulé la mobilité d'Aphis fabae et de deux clones de Myzus persicae, l'un sensible et l'autre résistant à des insecticides contenant des carbamates. Par ailleurs, le nombre de pucerons en train de sonder les feuilles ainsi que le nombre total de sondages ont été réduits et ainsi la transmission du virus de la mosaïque de la betterave (BMV) a été limitée. Dans des expériences à l'extérieur, la vitesse de propagation de BMV par des pucerons sur des plantes traitées à l'aldicarbe a été aussi plus limitée. Le nombre de plantes contaminées diminuait avec la distance de la source de contamination.