The fine structure of secretion by Plasmodium knowlesi merozoites during red cell invasion

The secretory organelles of Plasmodium knowlesi were studied ultrastructurally to examine their mode of action during invasion. The formation of lamellar structures in merozoite rhoptries within late stage schizonts is prevented by the protease inhibitors chymostatin and leupeptin. Under normal conditions vesicles lined by 6-nm membranes are formed in rhoptries during erythrocyte invasion. Stereoscopic viewing of tilted sections shows that where the merozoite apex contacts the parasitophorous vacuole (PV) membrane during invasion, a domed elevation of the PV surface lies within the mouth of the rhoptry duct in contact with the secretory matrix. The membrane of the early invasion pit is thinner (6 nm) than the red cell membrane elsewhere, and sheets of lamellar material are frequently present on the invasion pit surface. These findings support the proposal that the rhoptry-microneme complex is capable of generating membranous material and inserting it into the red cell surface in a controlled manner to create the parasitophorous vacuole. On the basis of this model, measurements from serial sections show that the rhoptries could provide enough material to create a membrane lining the parasitophorous vacuole, and, with the contribution of the microspheres, could double it to accommodate the early ring stage of the parasite.     

The induction of cross-links in soluble rat skin collagen in vitro

1. Starch-gel electrophoresis was used to investigate the subunit composition of salt-soluble and acid-soluble rat skin collagen. 2. Cross-linkage of collagen subunits in vitro was performed (a) when in fibrillar form and (b) when in solution. In the former case the increase in number of cross-links appeared to be predominantly intermolecular and in the latter case predominantly intramolecular.     

The Haemophilus influenzae sxy-1 mutation is in a newly identified gene essential for competence.

The sxy-1 mutation of Haemophilus influenzae causes a 100- to 1,000-fold increase in spontaneous natural competence. We have used mapping and sequencing to identify this mutation as a G-to-A transition in an open reading frame adjacent to the rec-1 locus. This mutation substitutes valine for isoleucine at amino acid 19 of the protein specified by this gene (now named sxy). A multicopy plasmid containing the wild-type sxy gene confers constitutive competence on wild-type cells. Cells carrying this plasmid exhibit, in all stages of growth, DNA uptake levels and transformation frequencies as high those normally seen only after full induction of competence by starvation; deletion of part of the sxy gene from the plasmid abolishes this effect. In contrast, a transposon insertion in sxy entirely prevents both DNA uptake and transformation, indicating that sxy encodes a function essential for competence. These findings suggest that sxy may act as a positive regulator of competence. However, because cells carrying the transposon-inactivated sxy::Tn allele grow slowly under conditions that do not induce competence, sxy may also have a role in noncompetent cells.     

New Zealand machair vegetation

Abstract. Machair vegetation is reported for the first time from New Zealand. The habitat is similar to that of British machairs in climate, topography and generally in soil. pH and CaCO₃ content are much lower through most of the sequence, though this difference may partly reflect the greater disturbance of British machair. Sea machair is present, predominantly comprising native species. This grades into machair proper, which contains many species found also in British machair. The machair includes Ammophila-occupied hillocks, a feature typical of British machair. Machair marsh is also present.     

Toxoplasmosis II. Studies of Animal Sera Using Complement-Fixation Tests

Serological studies were performed in guinea pigs, a sheep, calf, goat and two pigs experimentally infected with toxoplasmosis. The direct complement-fixation method was effective in detecting antibodies in guinea-pig, goat and sheep sera. The modified complement-fixation technique supplementing complement with normal bovine serum fraction, was required when testing bovine serum. With swine sera best reactions occurred in the indirect complement-fixation test and definite but low grade reactions were produced in the direct test after pro-complementary activity was removed by pH treatment of the sera. Allergic skin reactions were produced in the experimental animals but improvement in the antigen is necessary before the test could be used generally in the field as a diagnostic method for animal toxoplasmosis.     

Isolation from neutrophil membranes of a complex containing active NADPH oxidase and cytochrome b-245

The lipid composition and fluidity of basolateral membranes prepared from the mucosa of the proximal, middle and distal thirds of the rat small intestine were determined. Fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and a series of anthroyloxy fatty acid derivatives, is decreased in the distal third as compared to the proximal segments. This pattern is similar to that described previously for microvillus membranes. The decrease in fluidity of the distal as compared to the proximal membranes results from an increase in cholesterol content, cholesterol/phospholipid molar ratio and degree of saturation of the fatty acid residues. In the middle and distal thirds of the gut, the degree of saturation of the fatty acid residues is higher in microvillus as compared to basolateral membranes, accounting in part for the characteristically lower fluidity of the luminal membranes. The specific activity of the basolateral membrane (Na+ + K+)-dependent adenosine triphosphatase is significantly lower in the distal as compared to the proximal and middle thirds of the intestinal mucosa. Studies of the binding of [3H]ouabain indicate that this pattern results from fewer enzyme sites in the distal membranes.     

Slow fluorescence fluctuations following high light to low light or dark transitions in Chlamydomonas reinhardi.

Slow fluorescence transients in Chlamydomonas reinhardi arise after transitions from high light intensities to low light or dark conditions. Characteristics of the newly described transient phenomena include: (a) A slow biphasic decrease in fluorescence yield occurs in the dark, followed by an even slower, hour long, increase in fluorescence. (b) A similar, but faster, fluorescence yield decrease and subsequent increase also occurs during low intensity illumination periods separating high light intervals, or after transitions from high intensity to low intensity light. (c) Short (several seconds) flashes of light given during a dark period have no effect on the dark fluorescence decay, regardless of the flash frequency. Such flash regimes accurately monitor the dark decline of the M2 level by tracing the parallel decay of flash-generated P2 (Kautsky) peaks. However, flashes during a low light illumination period do influence the decay kinetics. Frequent flashes allow decay similar to that occurring in dark, but less frequent flashes inhibit the decrease in fluorescence yield.