Transbilayer distributions of red cell membrane phospholipids in unilamellar vesicles

The phospholipid organization in unilamellar vesicles comprised of various purified phospholipid components of monkey erythrocyte membrane was ascertained using phospholipase A2 and trinitrobenzenesulfonic acid as external membrane probes. The vesicles were formed by sonication or detergent dialysis and fractionated by centrifugation or gel permeation chromatography. Experiments were done to confirm that the phospholipase A2 treatments did not cause lysis or induce fusion of the vesicles. This enzyme hydrolysed only the glycerophospholipids in the outer surface of the vesicles. The amounts of the external phospholipids determined by this enzymatic method were verified using the chemical probe, trinitrobenzenesulfonic acid. The choline-containing phospholipids and phosphatidylethanolamine localized randomly in the two surfaces of sonicated vesicles (outer diameter, about 30 nm), whereas phosphatidylserine preferentially distributed in the inner monolayer. This phosphatidylserine asymmetry virtually disappeared in detergent dialysed vesicles (outer diameter, about 45 nm). Furthermore, inclusion of cholesterol in both the types of vesicles resulted in more random glycerophospholipid distributions across the plane of vesicles bilayer, presumably due to the cholesterol-induced increases in the size of vesicles. These results demonstrate that the transbilayer distribution of erythrocyte membrane phospholipids in unilamellar vesicles are controlled mainly by the surface curvature rather than by interlipid interactions, and therefore suggest that phospholipid-phospholipid and phospholipid-cholesterol interactions should not play any significant role in determining the membrane phospholipid asymmetry in red cells. It is proposed that this asymmetry primarily originates from differential bindings of phospholipids with membrane proteins in the two leaflets of the membrane bilayer.     

Metalloproteinase inhibitors from bovine cartilage and body fluids

Inhibitors of the mammalian metalloproteinases, collagenase, proteoglycanase and gelatinase were isolated from bovine cartilage (extracts and culture medium) and bovine amniotic fluid and serum. These inhibitors either bind or do not bind to concanavalin-A--Sepharose, with Mr (gel filtration) of about 30 000 and 20 000, respectively. Cartilage and chondrocyte culture media contained only concanavalin-A-binding inhibitors whereas cartilage extracts contained only a non-binding inhibitor: serum and amniotic fluid contained both forms of inhibitory activities. In moist biochemical respects, particularly in their abilities to inhibit metalloproteinases, all of the inhibitors were found to be similar. It is concluded that the forms of the inhibitors that differ in Mr may be closely related to the tissue inhibitor of metalloproteinases (TIMP) previously purified from rabbit and human sources. These findings help to clarify other studies on collagenase inhibitors and support the concept that TIMP-like inhibitors may be important in the control of connective tissue degradation.     

Target antigens in malaria transmission blocking immunity

Malaria transmission blocking immunity has been found to operate against two distinct phases of development of malaria parasites in the mosquito midgut: (i) against the extracellular gametes and newly fertilized zygotes shortly after ingestion by a mosquito of parasitized blood and (ii) against the zygotes during their subsequent development into ookinetes. Immunity is antibody-mediated and stage-specific. A set of three proteins, synthesized in the gametocytes, expressed on the surface of the gametes and newly fertilized zygotes and subsequently shed during later transformation of the zygotes, has been identified as the target antigens of anti-gamete fertilization blocking antibodies. A single protein, synthesized and expressed on the zygote surface during its development to ookinetes, has been identified as the target of antibodies which block the development of the fertilized parasites in the mosquito. Immunization of human populations against gamete or zygote antigens, while not directly protecting an immunized individual from inflection, would reduce the transfer of malaria within the population. Such immunity, in addition to reducing the overall rate of malaria transmission, would, if combined with a vaccine against the asexual (disease-causing) stages, reduce the chance of selection of parasites that are resistant to the asexual vaccine by preventing their entry into the mosquito population.     

Water relations in three species of theConvolvulaceae in the Indian arid zone

The relationship of water deficit, actual water content, area, water loss and stomatal behaviour in leaves of different insertion levels of three members of Indian arid zoneConvolvulaceae—Merremia aegyptia, M. dissecta andIpomoea pes-caprae were measured simultaneously in the month of May, 1974, when field conditions were extremely adverse for growth. The two former species loose far more water than the latter. The values measured varied considerably with the leaf insertion levels and they reversed inI. pes-caprae when compared withMerremia species.     

Axial ranking of residues in collagen in relation to edge association and fibril formation

In our earlier analysis of intermolecular interactions between collagen molecules, a major concern with the program employed is that it compared numbers of interactions between residues located on edges of defined, identical width and thus would not necessarily compare the same number of residues in each edge. This would be particularly true of some values of θ where well-defined vertical ranking of residues occurs. We have examined ranking of residues in relation to intermolecular edge association between bovine skin [α1(I)]₃ model collagen molecules by utilizing two different methods of counting intermolecular interactions between residues. The interaction peaks at θ = 27.69° and 36.00° are absent or relatively less intense in the plots obtained by utilizing radial distances between interacting residues instead of vertical bands of defined width. These studies suggest caution in accepting recently reported analyses of superhelix coiling of the collagen molecule which point to values of 27.69° or 36.00° for the twist of the superhelix. Although intramolecular interactions clearly point to interaction of collagen molecules at D intervals, they are insufficiently restricted in distribution to provide a reliable estimate of the superhelix angle by procedures so far employed.     

Proleptonchoides southindiae n. gen., n. sp., a New Leptonchoid from South India

Proleptonchoides southindiae n. gen., n. sp. (Dorylaimida: Leptonchidae), is described from soil around false tobacco (Lobelia excelsa) and cardamom (Elettaria cardamomurn) in South India. P. southindiae is prodelphic, has a short constricted esophageal bulb and flanged odontophore, and is phylogenetically close to Proleptonchus.     

Effect of boron on the pollen vitality and yield of rice plants (Oryza sativa L. var. Jaya)

Summary Rice plants were grown in sand cultures with nutrient solution including boron at 0, 1, 2.5 and 5 ppm concentrations.In general, supply of boron improved the pollen vitality of rice flowers. It was stimulating up to 2.5 ppm concentration in the nutrient solution, beyond which (i.e., at 5 ppm) inhibitory effects appeared. The availability of boron also increased the yield of rice grains in the same order.Stimulating effects of boron may be linked with greater availability of sugars, increased enzymatic activity and respiration which favoured better growth of pollen. Inhibitory effects of stronger concentration of boron (5 ppm) may be related with physiological depression and injury to protoplasm itself.