Characterization of the specific binding of rat apolipoprotein E-deficient HDL to rat hepatic plasma membranes

We have used a preparation of rat liver plasma membranes to study the binding of rat apolipoprotein E-deficient HDL to rat liver. The membranes were found to bind HDL by a saturable process that was competed for by excess unlabeled HDL. The binding was temperature-dependent and was 85% receptor-mediated when incubated at 4, 22 and 37 degrees C. The affinity of the binding site for the HDL was consistent at all temperatures, while the maximum binding capacity increased at higher temperatures. The specific binding of HDL to the membranes did not require calcium and was independent of the concentration of NaCl in the media. The effect of varying the pH of the media on HDL binding was small, being 30% higher at pH 6.5 than at pH 9.0. Both rat HDL and human HDL3 were found to compete for the binding of rat HDL to the membranes, whereas rat VLDL remnants and human LDL did not compete. At 4 degrees C, complexes of dimyristoylphosphatidylcholine (DMPC) and apolipoproteins A-I, A-IV and the C apolipoproteins, but not apolipoprotein E, competed for HDL binding to the membranes. At 22 and 37 degrees C, all DMPC-apolipoprotein complexes competed to a similar extent, DMPC vesicles that contained no protein did not compete for the binding of HDL. These results suggest that the rat liver possesses a specific receptor for apolipoprotein E-deficient HDL that recognizes apolipoproteins A-I, A-IV and the C apolipoproteins as ligands.     

Human sperm surface mapping with lectins.

Ten fluorescein isothiocyanate (FITC)-linked lectins [Bauhimia purpurea, Concanavalin A, Dolichos biflorus (DBA), Griffonia simplicifolia I, Griffonia simplicifolia II, Maclura pomifera, Arachis hypogea (PNA), Glycine max, Ulex europaeus (UEA) and Triticum vulgaris agglutinin] have been used to study their binding features on the human ejaculate spermatozoa. Qualitative changes in the labeling pattern have been observed in unfixed and acetone-treated spermatozoa. Furthermore, ultrastructural localization of some of the colloidal gold-linked lectins, namely PNA, UEA and DBA, has been attempted to delineate the binding domains of the specific sugars on the sperm surface. It needs to be emphasized that flow-cytometric methods employed in our study, which provide quantitative slant to qualitative data, should be utilized to evaluate the functional status of the spermatozoa.     

Membrane-binding sites for acyl carrier protein in Escherichia coli

We report that membrane vesicles of Escherichia coli contain protein-binding sites for acyl carrier protein. Scatchard analysis of the binding indicates a dissociation constant around 0.35 micrometers and a maximum number of protein-binding sites around 50 pmol per mg of membrane protein. Binding is on the inner membrane while the outer membrane is devoid of binding sites. These results are consistent with the fact that some acyl carrier protein-dependent enzymes implicated in phospholipid- and membrane-derived oligosaccharide biosynthesis are localized in the cytoplasmic membrane.     

The nitrogen cycle in shallow water sediment systems of rice fields Part III: The influence of N-application on the yield of rice

Fertilizer application to rice-fields in the river-deltas in the Mediterranean area is a potential menace for wildlife protection, through eutrophication.Fertilizer use shows a trend of increasing rates of N application. A rate for N of 200 kg ha^–1 has become normal and a rate of 400 kg ha^–1 has already been recorded.Denitrification causes large losses of N with the result that more fertilizer is applied. This is especially true for the Camargue (S-France), where N is applied long before the rice (Aryza sativa) can take it up.Therefore we have tried to develop techniques which need the application of smaller amounts of N which are used more efficiently. In order to do this we tried to establish a N budget for rice-fields.Experiments were therefore set up in the field (plots of 550 m²) and in pots (2–3 l). Our results suggest that a late application of N (e.g. when the rice shows signs of N-deficiency by becoming yellowish), but at lower concentrations (70 kg ha^–1) can produce the same ultimate yield. The introduction of carp without any further input of N produced the same final yield.The N budget shows that 15±1.5 g m^–2 of N is needed for a normal crop. N losses due to denitrification may be as high as 12.2–13.6 g m^–2 of N. The input by irrigation water may provide up to about 20% of the input; N fixation is negligible. We estimate that 25–50% of the N missing in the budget comes from minderalization of the organic N pool in the soil. Denitrification may render part of this pool bio-available by oxidation. In sum, this work has revealed some surprising effects with potentially important consequences for farming practice and, in consequence, for conservation.     

Definition of meningococcal class 1 OMP subtyping antigens by monoclonal antibodies

The subtypes of meningococci are defined by antigenic determinants on the class 1 outer membrane proteins. The established subtypes, designated by P1 and a number according to the prototype reference strain on which they were first recognized by monoclonal antibodies, includes P1.2, P1.9, P1.15 and P1.16. We have investigated more prototype reference strains, using new monoclonal antibodies, and identified the new subtypes P1.1, P1.6 and P1.1,16. The P1.1,16 epitope is found on both the P1.1 and the P1.16 reference strains, but not on all P1.1 and P1.16 strains and can occur independently from the P1.1 and the P1.16 epitopes. It appears that class 1 outer membrane proteins contain at least two independent subtype-specific epitopes. For clarity, we now redefine P1.1,16 as P1.7, permitting thus the identification of strains of P1.1, P1.1,7, P1.7, P1.7,16 and P1.16 subtypes. It can clearly be expected that more class 1 outer membrane protein determinants will be recognized as more monoclonal typing antibodies are produced. The monoclonal antibodies now available to us can subtype 80-90% of group B and C meningococci; they also react with group A meningococci, but not with other Neisseriae. The immunological dissection of these subtyping antigens will improve our understanding of the relationship between components of the bacteria and the induction or prevention of disease.     

The Chlamydomonas cell wall degrading enzyme, lysin, acts on two substrates within the framework of the wall

The Chlamydomonas cell wall is a multilayered, extracellular matrix containing 20-25 proteins and glycoproteins, many of which are highly enriched in hydroxyproline. 80-90% of the wall protein is located in a crystalline portion of the wall that is soluble in sarkosyl-urea solutions as well as in chaotropic salts. Although the wall has no cellulose it contains a noncrystalline, highly insoluble framework portion that is responsible for the integrity and overall shape of the wall. In the present report we show that the framework of the wall is composed of two components that are acted upon by lysin, a wall degrading enzyme released by mating gametes. One, which makes up the major portion of the framework, is insoluble upon boiling in SDS-PAGE sample buffer. Lysin treatment of this portion leads to its physical degradation and the concomitant appearance of several SDS-dithiothreitol-soluble polypeptides ranging in relative molecular mass from greater than 400,000 to less than 60,000. The second component is the flagellar collar. This hollow cylinder composed of striated fibers aligned in parallel array serves as the tunnel in the wall through which the flagella protrude. Our evidence indicates that the primary collar polypeptide is a 225,000-Mr molecule that itself has at least two functional domains. One domain, contained in a 185,000-Mr fragment, permits the self-association of the molecules to form the main body of the collar. The second part of the molecule anchors the collar to the wall framework via sarkosyl-urea-insensitive, SDS-dithiothreitol-sensitive linkages.