Choline Administration Elevates Brain Phosphorylcholine Concentrations

Abstract: The phosphorylcholine concentration of rat brain rises and falls in response to parallel changes in the concentration of circulating choline. A single oral dose of choline chloride (20 mmol/kg) elevated whole-brain concentrations of both choline and phosphorylcholine 5 h after administration; a greater proportion of exogenously administered choline was retained by the brain in its phosphorylated form than as the free arnine. Striatal phosphorylcholine concentrations were elevated within 2 h of choline administration and continued to be significantly greater than control values for up to 34 h after treatment. The response of striatal choline levels to exogenous choline was of shorter duration than that of phosphorylcholine and was correlated with a significant increase in striatal acetylcholine concentrations. The consumption of a choline-free diet for 7 days lowered both serum choline and striatal phosphorylcholine concentrations, but had no effect on striatal choline or acetylcholine. These results suggest that choline kinase is unsaturated by its substrate in vivo and may thus serve to modulate the response of brain choline concentrations to alterations in the supply of circulating choline.     

Mathematical model of the activation of prothrombin by factor X a and factor V t

A mathematical model of prothrombin activation is being proposed which includes the feedback mechanism of thrombin and the alteration of factor V by thrombin. This model is in good agreement with experimental data for the dependence of the rate of thrombin formation on the concentrations of factors V and X _a . In particular, it correctly predicts the existence and location of a maximum in both of these cases.     

Interaction of protein kinase C with phosphatidylserine. 2. Specificity and regulation.

The roles of specific and nonspecific interactions in the regulation of protein kinase C by lipid have been examined. Binding and activity measurements reveal two mechanisms by which protein kinase C interacts with membranes: (1) a specific binding to the activating lipid phosphatidylserine and (2) a nonspecific binding to nonactivating, acidic lipids. The specific interaction with phosphatidylserine is relatively insensitive to ionic strength, surface charge, and the presence of nonactivating lipids. The two second messengers of the kinase, diacylglycerol and Ca2+, increase markedly the affinity of the kinase for phosphatidylserine. In contrast, the nonspecific interaction is sensitive to ionic strength and surface charge, and is unaffected by diacylglycerol. These results suggest that electrostatic interactions promote the binding of protein kinase C to membranes but the cooperative and selective binding of phosphatidylserine is the dominant driving force in a productive protein-lipid interaction.     

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.     

Partial trisomy 20p resulting from a recombination of a familial pericentric inversion

Summary Recombination of an inherited pericentric inversion of chromosome 20 has given rise to a child with partial trisomy 20p. To our knowledge no previous familial inversions of this chromosome have been described in the literature.     

Solid-state 15N NMR of oriented lipid bilayer bound gramicidin A'

Highly oriented samples of lipid and gramicidin A' (8:1 molar ratio) have been prepared with the samples extensively hydrated (approximately 70% water v/w). These preparations have been shown to be completely in a bilayer phase with a transition temperature of 28 degrees C, and evidence is presented indicating that the gramicidin is in the channel conformation. An estimate of the disorder in the alignment of the bilayers parallel with the glass plates used to align the bilayers can be made from the asymmetry of the nuclear magnetic resonances (NMR). Such an analysis indicates a maximal range of disorder of +/- 3 degrees. Uniformly 15N-labeled gramicidin has been biosynthesized by Bacillus brevis grown in a media containing 15N-labeled Escherichia coli cells as the only nitrogen source. When prepared with labeled gramicidin, the oriented samples result in high-resolution 15N NMR spectra showing 12 resonances for the 20 nitrogen sites of the polypeptide. The frequency of the three major multiple resonance peaks has been interpreted to yield the approximate orientation of the N-H bonds in the peptide linkages with respect to the magnetic field. These bond orientations are only partially consistent with the extant structural models of gramicidin.