Differential binding of mannose-specific lectins to the carbohydrate chains of fibrinogen domains D and E

The interaction of fibrinogen with the mannose-specific lectins concanavalin A (ConA), its acetyl derivative (Ac-ConA) and Lens culinaris agglutinin (LcH) was studied. Both ConA and LcH interact specifically with individual fibrinogen B beta and gamma chains and with denatured fragments D and E. However, analysis of the binding data shows that four moles of Ac-ConA are bound per mole of fibrinogen with two sets of binding sites (Kd1 = 2.4 microM and Kd2 = 16.6 microM; n1 = n2 = 2) while only two moles of LcH are bound per mole of fibrinogen (Kd = 2.6 microM). Ultracentrifugation studies are also in agreement with the presence in the fibrinogen molecule of two and four binding sites for LcH and Ac-ConA, respectively. No aggregates of fibrinogen formed through LcH or Ac-ConA linkages are observed. The use of a crosslinking reagent and ultracentrifugal analysis of the lectin-fibrinogen fragments D1 and E complexes indicated that ConA, as well as Ac-ConA, interact with both fragments D and E while LcH interacts only with fragment D. Furthermore, the binding of ConA to both D and E domains in the intact fibrinogen molecule is clearly demonstrated by using a bifunctional reagent. The bivalent character of ConA tetramers may be misinterpreted as a lack of accessibility of the lectin to two of the four carbohydrate chains of fibrinogen. The differential binding of LcH and ConA to the carbohydrate chains of fibrinogen can be related to a different exposure of the oligosaccharide in D and E fragments and domains and to the different requirements of both lectins for their binding to glycoproteins.     

A novel group of very long chain polyenoic fatty acids in dipolyunsaturated phosphatidylcholines from vertebrate retina

Dipolyunsaturated phosphatidylcholines from bovine retina contain a whole series of unusual fatty acids. Methyl esters from these acids are very strongly retained on polar and nonpolar gas-liquid chromatography stationary phases. On thin layers of silica-AgNO3, they separate as tetra-, penta-, and hexaenoic fatty acid methyl esters. After hydrogenation, the three polyunsaturated fractions give the same series of saturated methyl esters, having 20 (or 22)-36 carbon atoms. High pressure liquid chromatography, as well as gas-liquid chromatography, indicates that the new components of the three fractions are even-carbon homologs of well known polyenoic fatty acids of the n-6 and n-3 families, since they behave as series of 20-36-carbon tetraenoic (n-6), pentaenoic (n-3 and n-6), and hexaenoic (n-3) fatty acids. Their occurrence in phospholipid molecules also having docosahexaenoate (22:6) explains the separation of major dipolyunsaturated phosphatidylcholines from retina into dodecaenoic, undecaenoic, and decaenoic fractions after argentation thin layer chromatography. Using high pressure liquid chromatography, the latter are resolved into individual species having 10-12 double bonds and 42-58 carbon atoms. The unusual PCs are thus endowed not only with the highest degree of unsaturation, but with the longest hydrocarbon chains yet reported for vertebrate glycerophospholipids. It is shown that phosphatidylcholines containing the novel fatty acids are highly concentrated in photoreceptor membranes and that they occur in the retina of vertebrates so distant in evolution as fish, birds, and various mammals.     

Studies on evolutionary and selective properties of hypercycles using a Monte Carlo method

Summary The most relevant properties of hypercycles were previously studied mainly from a theoretical point of view. We have developed a Monte Carlo method simulating hypercyclic organization to obtain information about the dynamics of this prebiotic organization. Nucleation, growth, and selective properties have been tested and the results obtained are in good agreement with those of the theoretical predictions. The influence of hypercyclic organization of the error threshold has also been studied. As a consequence of the emergence of a hypercycle, the value of this threshold decreases. The amount of this decrease depends on the population size. Moreover, for some interval of quality factor values, either the hypercycle organization or an error catastrophe can be produced, depending on the initial conditions. The influence of these phenomena on both the dynamic behavior and evolutionary advantages of the hypercycle, as well as their decisive roles on genome size, are discussed.Presented at the FEBS Symposium on Genome Organization and Evolution, held in Crete, Greece, September 1–5, 1986     

Labeling of lipids of retina subcellular fractions by [1-14C]eicosatetraenoate (20:4(n-6)) docosapentaenoate (22:5(n-3)) and docosahexaenoate (22:6(n-3))

(1-14C)-labeled (n-6) eicosatetraenoate, (n-3) docosapentaenoate and (n-3) docosahexaenoate (20:4, 22:5 and 22:6, respectively) are efficiently taken up and actively esterified into the lipids of bovine retina after 2 h incubation. Photoreceptor membranes, mitochondria, microsomes and postmicrosomal supernatants, which display significant differences in phospholipid and fatty acid compositions, are isolated after such incubations to study the labeling of lipids. The lipid classes preferentially labeled with the acids (1) largely differ among and within subcellular fractions, while (2) some common features in the treatment of the three polyenes are observed in each fraction. In all of them, the three acids are actively incorporated in phosphatidylcholine; ethanolamine glycerophospholipid, phosphatidylserine (PS) and phosphatidylinositol (PI) are highly labeled with 22:6, 22:5 and 20:4 respectively; within ethanolamine glycerophospholipid, the three label phosphatidylethanolamine in preference to plasmenylethanolamine. Most of the 14C esterified in mitochondria is in phospholipids. The endoplasmic reticulum produces in addition highly labeled triacylglycerols, also found in cytosol. High levels of 14C-labeled diacylglycerols are observed exclusively in photoreceptor membranes, where the specific radioactivity of PI is very high. The total amounts of 14C incorporated (1) are in general similar within a given fraction for the three polyenes, but (2) largely differ among fractions. The labeling of the highly unsaturated phospholipids of photoreceptor membranes is the lowest, while the postmicrosomal supernatant (whose lipids are relatively the poorest in polyenoic fatty acids) contains most of the labeled lipids isolated from retinas under these conditions. The results indicate that polyunsaturated species of retina phospholipids undergo an active synthesis and turnover, as well as an intense intracellular traffic among membranes.     

Effect of lectin-binding to fibrinogen D and E domains on coagulation and fibrinolysis

The effect on fibrinogen coagulation and fibrinolysis of the mannose-specific lectins concanavalin A, its acetyl derivative and Lens culinaris agglutinin was studied. Concanavalin A and acetyl-concanavalin A, which bind to the four carbohydrate chains of fibrinogen, and L. culinaris agglutinin, which only binds to the carbohydrate present in fibrinogen D domains, has the same effect on the coagulation rate: an inhibition at low lectin concentrations and an increase at high concentrations. On the other hand, L. culinaris agglutinin does not alter fibrin crosslinking while acetyl-concanavalin A produces a slight inhibition of both gamma-gamma and alpha-polymer formation. However, this effect is very small when compared with the clear inhibitory effect produced by concanavalin A. Concanavalin A and acetyl-concanavalin A have an inhibitory effect on the rate of fibrin clot lysis proportional to the lectin concentration. Nearly 100% inhibition was obtained when two lectin-binding sites were occupied by either concanavalin A or acetyl-concanavalin A. However, L. culinaris agglutinin has a clearly weaker effect and more than 50% inhibition was not observed. The comparative study of the effect of the three lectins on fibrinolysis as well as on the formation of fibrinogen aggregates suggests that the inhibitory effect of concanavalin A and acetyl-concanavalin A is primarily due to their binding to the carbohydrate chains of fibrinogen E domain.     

Labeling of phosphatidylcholines of retina subcellular fractions by [1-14C]eicosatetraenoate (20:4(n-6)), docosapentaenoate (22:5(n-3)) and docosahexaenoate (22:6(n-3))

The labeling of molecular species of phosphatidylcholine (PC) has been studied in bovine retinas incubated for 2 h with (1-14C)-labeled (n-6) eicosatetraenoate (n-3) docosapentaenoate and (n-3) docosahexaenoate (20:4, 22:5 and 22:6, respectively) and in four subcellular fractions isolated after such incubations. Of the total radioactivity incorporated in PC, the following percentages of the above fatty acids, respectively, are found in its dipolyunsaturated species: 58, 56 and 53% in rod outer segments; 29, 41 and 49% in mitochondria; 24, 28 and 39% in microsomes; 12, 14 and 16% in postmicrosomal supernatants; 28, 36 and 58% in entire retinas. The remainder percentages are in tetra-, penta- and hexaenoic species of PC, respectively. The levels of pentaenoic species in the PCs of all fractions are similar, while tetraenes are lowest and hexaenes highest in photoreceptor membranes. Dipolyunsaturated species are highly concentrated in photoreceptor membranes, but are minor components of mitochondrial, microsomal and cytosolic PC. The specific radioactivities of tetraenoic, pentaenoic and hexaenoic PCs are decreasingly lower in the following order: postmicrosomal supernatants, microsomes, mitochondria, photoreceptor membranes. In contrast, the specific radioactivities of dipolyunsaturated PCs are higher in mitochondria and microsomes than in the other fractions, especially with 22:5 and 22:6. It is suggested that mitochondria as well as the endoplasmic reticulum could play a role in the synthesis and further modifications of dipolyunsaturated PCs before being supplied to photoreceptor membranes.     

A complex balanced chromosomal rearrangement in repeated abortions

Summary A double balanced reciprocal translocation involving four chromosomes, t(1;19;6;14) (1p11; 19p11; 6q25; 14q21), was found in the phenotypically normal husband in a couple referred because of repeated abortions. Reciprocal translocations, t(6;14), had been transmitted by his mother, his father being apparently homozygous for a translocation comprising pairs 1 and 19-t(1;19)(1;19). The genetic consequences of this complex chromosomal rearrangement are analyzed.     

Salinity and germination of annual Melilotus from the Guadalquivir delta (SW Spain)

The germination response to NaCl treatments has been studied in Melilotus seed populations collected from saline and non-saline soils in the Guadalquivir delta. The rank orders for salt tolerance and seed weight were the same in the threeMelilotus species living in this area:Melilotus messanensis>M. segetalis>M. indica. Within the species, differences in germination response to salinity were found inM. indica (6 populations) andM. segetalis (8 populations). The relationship between salt tolerance during germination and salinity of maternal habitat is discussed.     

Leghemoglobin in Lupin Plants (Lupinus albus cv Multolupa)

Leghemoglobin was localized by immunogold techniques in nodules of Lupinus albus cv Multolupa inoculated with Bradyrhizobium sp. (Lupinus) strain ISLU 16. The protein localization was performed in nodules embedded in Spurr's and Araldite epoxy resins and Lowycryl K4M. A very good preservation of both the ultrastructure and antigenicity was obtained with the tissues embedded in Araldite following glutaraldehyde fixation and unpostfixed in osmium tetroxide. Lupin leghemoglobin is a stable and abundant protein which allows a conventional method to be safely used for localization of leghemoglobin. Labeling of leghemoglobin was specifically confined to the cytosol matrix and nuclei. Gold particles were never observed in the peribacteroidal spaces nor in the cytoplasmic organelles of the infected cells. Decrease of leghemoglobin was observed when the plants were grown with 10.7 micromolar and 21.4 micromolar of nitrate.