Interaction of the serum amyloid A proteins with phospholipid

The serum amyloid A proteins (SAA) are transported in plasma in association with the high density lipoproteins. We have studied the solution properties of two of the polymorphic forms of SAA, SAA1 and SAA4, and compared the lipid-binding properties of SAA4 to those of the well characterized apolipoproteins, apo-A-I, apo-A-II, and apo-C-III. SAA4 was monomeric at pH 2.9 but considerable self-association was demonstrated at pH 8.2, even in the presence of 1.0 M guanidine HCl. SAA4 differed from the apolipoproteins in its ability to disrupt multilamellar dimyristoylphosphatidylcholine (DMPC) liposomes and generate bilayer discs. Apo-A-I, apo-A-II, and apo-C-III reduced the turbidity of DMPC dispersions at protein:lipid molar ratios of 1:200. SAA4, however, increased turbidity at molar ratios of 1:250 and 1:100 even when preincubated in guanidine HCl before addition to liposomes. Optical density decreased only at ratios of 1:50 and 1:25. At an SAA4:DMPC ratio of 1:50, discoidal particles (long axis, 28.1 nm; short axis, 4.4 nm) were formed which were similar to those produced by apo-C-III. Lipid binding induced changes in SAA4 conformation similar to those observed in the apolipoproteins. The alpha-helical content and intrinsic tryptophanyl fluorescence were increased and quenching of tryptophanyl fluorescence by acrylamide was reduced in the presence of DMPC. In addition, SAA4 as well as the apolipoproteins broadened the range and increased the temperature of the gel-liquid crystal transition temperature of DMPC.     

Tidal flows and sediment budgets for a salt-marsh system,Essex, England

Studies of tidal flows in salt-marsh creeks in Essex, England, show large variations in water velocity during different tidal cycles, particularly between tides below, at, and above marsh level. Water level, velocity and suspended sediment concentration have been monitored at 5-min intervals during 700 tidal cycles during the year March 1982–March 1983, and the data are being used to calculate sediment budgets for the creek system studied. Completed analyses for two of the tidal cycles show a large positive sediment flux. Because of the importance of velocity in controlling total discharge through a creek cross-section, and hence its effect on total sediment movement, we cannot extrapolate from these two below-marsh tides to any general conclusions about marsh erosion or accretion. We use these preliminary data both to demonstrate our methods and to indicate some of the complexities involved in the analysis.Acknowledgements: This work has been supported by the Natural Environment Research Council. We thank the Philip Lake Fund for financial assistance and the Department of Geography, Cambridge University, for much material support. Mr D. J. Fisher kindly gave access to his land, and Mr W. Bailey helped us greatly. We also thank Mr A. St Joseph for his help, Mr M. Diver for practical support, and Dr J. S. Pethick for discussion.     

3. Control of sex expression in conifers

Despite considerable progress in recent years in the promotion of flowering in conifers, relatively little is known about the endogenous control of sex expression or its practical manipulation to aid pollen and crop management in seed orchards. Well defined patterns of sexual zonation exist within the tree crown and shoot, and these appear to be associated with hormonal and possibly nutritional gradients. No firm conclusions, however, are possible regarding the specific role(s) of different PGRs in sex expression, this being as much as a problem of lack of critical study as the complexity of the process itself. Whether a PGR such as gibberellins or auxins, or a cultural treatment that itself may influence endogenous hormone levels, primarily promotes female or male flowering often depends on the position within the crown of the shoot being treated, and its timing in relation to stage of primordia development. Photoperiod also may be involved- short days favoring females and long days males, at least in some species- although its role in controlling sex expression is by no means clear. Practical manipulation of sex expression may be possible through selective crown pruning, different PGR combinations, treatment timing and/or photoperiod control, but the development of such techniques for operational use will require a better basic understanding of the endogenous regulatory mechanisms involved.     

Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders

Background  

Introductions of non-native tiger salamanders into the range of California tiger salamanders have provided a rare opportunity to study the early stages of secondary contact and hybridization. We produced first- and second-generation hybrid salamanders in the lab and measured viability among these early-generation hybrid crosses to determine the strength of the initial barrier to gene exchange. We also created contemporary-generation hybrids in the lab and evaluated the extent to which selection has affected fitness over approximately 20 generations of admixture. Additionally, we examined the inheritance of quantitative phenotypic variation to better understand how evolution has progressed since secondary contact.     

Kinetic analysis of protonation of a specific site on a buffered surface of a macromolecular body

The kinetics of protonation of a specific site on a macromolecular structure (micelle) in buffered solution was studied with the purpose of evaluating the effect of buffer on the observed dynamics. The experimental system consisted of the following elements: Brij 58 micelles serving as homogeneous uncharged macromolecular bodies, bromocresol green, a well-adsorbed proton detector, and 2-naphthol-3,6-disulfonate as a proton emitter in the bulk. Imidazole was the mobile buffer while neutral red, which has a high affinity for the micellar surface, served as the immobile buffer. An intensive laser pulse ejects a proton from the proton emitter, and the subsequent proton-transfer reactions are measured by fast spectrophotometric methods. The dynamics of proton pulse in buffered solution are characterized by a very rapid trapping of the discharged protons by the abundant buffer molecules. This event has a major effect on the kinetic regime of the reaction. During the first 200 ns the proton flux is rate limited by free-proton diffusion. After this period, when the free-proton concentration decayed to the equilibrium level, the relaxation of the system is carried out by the diffusion of buffer. Thus in the buffered biochemical system, at neutral pH, most of proton flux between active sites and bulk is carried out by buffer molecules--not by diffusion of free protons. Surface groups on a high molecular weight body exchange protons among them at a very fast rate. This reaction has a major role on proton transfer from a specific site to the bulk.(ABSTRACT TRUNCATED AT 250 WORDS)