Changes in endogenous polyamine levels are associated with differentiation in Dictyostelium discoideum.

This is the first report correlating levels of polyamines and its fractions with differentiation in Dictyostelium discoideum. Temporal changes in endogenous levels of free, conjugated and bound putrescine, spermidine and spermine were analysed at critical stages of morphogenesis in this organism. No spermine was found at any given stage and putrescine was the most abundant polyamine. There was a sharp increase in the levels of both free (and total) and conjugated forms of putrescine and spermidine at the slug stage as compared to the growth phase. The levels of putrescine and spermidine were found to be higher in isolated prespore cells as compared to the prestalk cells. Remarkably, the levels of polyamine decreased at the early culminant stage. Data suggest that a moderate level of polyamines is needed for growth but it is important to have high levels of polyamines at the time of differentiation.     

Conformational study of fragments of envelope proteins (gp120: 254-274 and gp41: 519-541) of HIV-1 by NMR and MD simulations.

The envelope proteins, gp 120 and gp41 of HIV-1, play a crucial role in receptor (CD4+ lymphocytes) binding and membrane fusion. The fragment 254-274 of gp120 is conserved in all strains of HIV and, as a part of the full gp120 protein, behaves as 'immunosilent', but as an individual fragment it is 'immunoreactive'. When this fragment binds to its receptor, it activates the fusion domain of gp41 allowing viral entry into the host CD4+ cells. The conformation of fragment 254-274 of the gp120 domain and fragment 519-541 of the gp41 domain was studied by NMR and MD simulations. The studies were carried out in three varied media--water, DMSO-d6 and hexafluoroacetone (HFA). The fusogenic nature of the gp41 domain peptide was investigated by 31P NMR experiments with model bilayers prepared from dimyristoyl-L-alpha-phosphatidylcholine (DMPC). The solvent was seen to exert a major effect on the structure of the two peptides. Fragment (254-274) of gp120 in DMSO-d6 had a type I beta-turn around the tetrad Val9-Ser10-Thr11-Gln12 while in HFA a helical structure spanning the region Ile5 to Gln12 was seen with the remaining part of the peptide in a random coil structure. It is possible that the beta-turn may constitute an initiation site for the formation of the helix. In water at pH 4.5, the peptide adopted a beta-sheet. The NMR results for fragment 519-541 of gp41 are conclusive of a beta-sheet structure in DMSO-d6, a conformation which may help in insertion into the membrane, a notion also put forward by others. The 31P NMR studies of DMPC vesicles with this fragment show its fusogenic nature, promoting fusion of unilamellar vesicles to larger agglomerates like multilamellar ones.     

Effects of food quality on individual growth and development in the freshwater copepod Boeckella triarticulata

To quantify the demographic effects of food quality, and specificallyof the ‘poorquality’ cyanobecterium Anabaena flos-aquae,we reared individual Boeckella triarticulata (Copepoda, Calanoida)on two diets (monospecific Cryptomom sp. versus mixed Cryptomonas-Anabanmadiets) and quantified individual growth and developmental trajectoriesby examining exuviae produced at each molt, from hatching tomaturity. Size at molting was less variable among individuals,within and between diets, than age. Food quality had significanteffects on male sizes at molting and on stage-specific dailygrowth rates of both sexes; these effects were strongest duringlate naupliar and all copepodite stages Tke med Cryptomonas-Anabaenadiet significantly slowed development, particularly of copepoditestages. As a consequence of these effects, individuals raisedon the mixed diet were smaller and older at maturity. Withina given diet, individual differences explained much, if notmost, of the variation exhibited in growth and development.By following growth and development of a large number of individualsthroughout their Life cycles, we show that individual femalesproduce variable offspring, indicative of a bet-hedging life-historystrategy, and that B.triarticulata (like other calanoids) cangrow, develop and survive on diets that include ‘poorquality’ cyanobacteria. ¹Present address: Department of Biological Sciences, Universityof Rhode Island, Kingston, RI 02881, USA     

Reactions of linoleic acid peroxyl radicals with phenolic antioxidants: a pulse radiolysis study

Linoleic acid peroxyl radicals (LOO.) can be viewed as model intermediates occurring during lipid peroxidation processes. Formation and reactions of these species were investigated in aqueous alkaline solution using the technique of pulse radiolysis combined with kinetic spectroscopy. Irradiation of linoleic acid in N2O/O2-saturated solutions leads to a mixture of peroxyl radical isomers, whereas reaction of 13-hydroperoxylinoleic acid (13-LOOH) with azide radicals in N2O-saturated solution produces 13-LOO. radicals specifically. These peroxyl radicals cannot be observed directly, but their reactions with the two flavonols, kaempferol and quercetin, acting as radical-scavenging antioxidants, produced strongly absorbing aroxyl radicals (ArO.). The same aroxyl radicals were generated by .OH and N3. with rate constants exceeding 10(9) dm3 mol-1 s-1. Applying a reaction scheme that includes competing generation and decay reactions of both LOO. and ArO. radicals, we derived individual rate constants for LOO. reactions with the phenols (greater than 10(7) dm3 mol-1 s-1), with the aroxyl radicals to form covalent adducts (greater than 10(8) dm3 mol-1 s-1), as well as for their bimilecular decay (3.0 X 10(8) dm3 mol-1 s-1). These results demonstrate the high reactivity of both fatty acid peroxyl radicals and the flavone antioxidants in aqueous solution.     

Patterns of male reproductive success in Crepidula fornicata provide new insight for sex allocation and optimal sex change

The size-advantage model and sex-allocation theory are frequently invoked to explain the evolution and maintenance of sequential hermaphroditism in many taxa. A test of current theory requires quantitative estimates of reproductive success and knowledge of the relationship between reproduction and size for each gender. Reproductive success can be difficult to measure. In species where polyandry occurs, it can be quantified only by determining paternity of offspring. We employed microsatellite loci to establish paternity for 12 families of Crepidula fornicata, where a family is defined as a single female, her brood, and the males stacked on top of her. Genetic data were analyzed and paternity was assigned to a single potential father for more than 83% of the offspring tested. Estimates of reproductive success revealed that one male within the family fathered the majority of offspring and that he was usually the largest male and the one closest to the brooding female. The dominant male's success also tended to decrease as the number of mature males within the family increased. Our results suggest that sperm competition could be a driving force in determining male reproductive success and the timing of sex change in C. fornicata.