A High-End Estimate of Sea Level Rise for Practitioners.

Sea level rise (SLR) is a long-lasting consequence of climate change because global anthropogenic warming takes centuries to millennia to equilibrate for the deep ocean and ice sheets. SLR projections based on climate models support policy analysis, risk assessment and adaptation planning today, despite their large uncertainties. The central range of the SLR distribution is estimated by process-based models. However, risk-averse practitioners often require information about plausible future conditions that lie in the tails of the SLR distribution, which are poorly defined by existing models. Here, a community effort combining scientists and practitioners builds on a framework of discussing physical evidence to quantify high-end global SLR for practitioners. The approach is complementary to the IPCC AR6 report and provides further physically plausible high-end scenarios. High-end estimates for the different SLR components are developed for two climate scenarios at two timescales. For global warming of +2°C in 2100 (RCP2.6/SSP1-2.6) relative to pre-industrial values our high-end global SLR estimates are up to 0.9 m in 2100 and 2.5 m in 2300. Similarly, for a (RCP8.5/SSP5-8.5), we estimate up to 1.6 m in 2100 and up to 10.4 m in 2300. The large and growing differences between the scenarios beyond 2100 emphasize the long-term benefits of mitigation. However, even a modest 2°C warming may cause multi-meter SLR on centennial time scales with profound consequences for coastal areas. Earlier high-end assessments focused on instability mechanisms in Antarctica, while here we emphasize the importance of the timing of ice shelf collapse around Antarctica. This is highly uncertain due to low understanding of the driving processes. Hence both process understanding and emission scenario control high-end SLR.

Relaxation spectra of gramicidin dimerization in a lipid bilayer membrane.

The kinetics of formation and dissociation of gramicidin dimers in a lipid bilayer membrane have been studied by pressure-jump and electric field-jump methods. The traditional AC-coupled pressure-jump apparatus has been modified so that a known DC-voltage drop is maintained across a Teflon cell divided by a septum with a hole for membrane formation. From the response of the amplified output voltage after the pressure release, information about the kinetics of channel (dimer) formation is obtained. In addition, using the same apparatus, electric field-jump measurements were performed on the gramicidin/membrane system. In asolectin/7-dehydrocholesterol (5:1) membranes at 25 +/- 0.1 degrees C, the best fit to the pressure-jump data gives a dimer dissociation rate constant of 0.5 +/- 0.3 s-1. The standard volume change for dimerization determined from the amplitude of the pressure-jump experiments is -66 +/- 35 cm3/mol. Rate data determined by the electric field-jump method are consistent with the pressure-jump values; results obtained with either technique are compatible with other determinations of the kinetics of dimerization on gramicidin/membrane systems.

Conformation of the gramicidin A channel in phospholipid vesicles: a fluorine-19 nuclear magnetic resonance study.

The membrane conformation of the peptide ionophore gramicidin A is shown by 19F NMR to be described by the N-terminal to N-terminal beta LD helical dimer model proposed by Urry [Urry, D.W. (1971) Proc. Natl. Acad. Sci. U.S.A. 68, 672-676]. Fully active analogues of gramicidin with 19F labels at both the N- and C-termini are prepared synthetically. Labeled peptides are incorporated into small unilamellar vesicles of dimyristoylphosphatidylcholine. Measurements of the accessibility of the labels to either aqueous or lipophilic paramagnetic probes show that the N-terminus of gramicidin is located in the membrane interior and the C-terminus is at the membrane surface. Of the specific models proposed for the structure of gramicidin, these data are consistent only with that of Urry. The C-terminal 19F NMR peak in vesicles actually consists of three overlapping peaks. Experiments with the aqueous shift reagent Tm3+ show that C-terminal 19F nuclei in the inner and in the outer leaflets of vesicles resonate at different frequencies. The outer leaflet peak in turn consists of two overlapping peaks, possibly due to a local rearrangement of the C-terminal label.

Lateral mobility of phospholipid and cholesterol in the human erythrocyte membrane: effects of protein-lipid interactions.

The phospholipid and cholesterol derivatives N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine (NBD-PE) and N1-cholesterylcarbamoyl-N8-(7-nitro-2,1,3-benzoxadiazol-4-yl )-3,6-dioxaoctane-1 , 8-diamine (NBD-Chol), respectively, were incorporated into egg phosphatidylcholine/cholesterol multilamellar liposomes, human erythrocyte ghost membranes, and multilamellar liposomes derived from extracted human erythrocyte membrane lipids. The lateral mobility of these probes in the plane of the various membranes was measured by using the fluorescence photo-bleaching recovery technique. NBD-PE and NBD-Chol manifested identical lateral mobilities in egg phosphatidylcholine/cholesterol multilamellar liposomes over the range of temperatures from 10 to 37 degrees C and the range of cholesterol mole fractions from 0.0 to 0.5, and in erythrocyte ghost membranes and erythrocyte membrane lipid-derived multilamellar liposomes over the range of temperatures from 15 to 37 degrees C. The weak temperature dependence of the lateral diffusion coefficients of the lipid probes in both artificial and erythrocyte ghost membranes is consistent with the lack of a phase transition in any of these systems over the temperature range studied. Both NBD-PE and NBD-Chol diffuse 4-fold faster in liposomes derived from extracted erythrocyte membrane lipids (D = 8.0 X 10(-9) cm2 s-1 at 37 degrees C) than in the ghost membranes themselves (D = 2.1 X 10(-9) cm2 s-1 at 37 degrees C), suggesting a significant restriction of lipid lateral mobility by membrane protein in the human erythrocyte membrane.

Use of a fluorescent cholesterol derivative to measure lateral mobility of cholesterol in membranes.

N1-Cholesterylcarbamoyl-N8-(4-nitrobenzo-2-oxa-1,3-diazole)-3,6-dioxaoctyl-1,8-diamine (NBD-Chol), a new fluorescent derivative of cholesterol, was incorporated into L-alpha-dimyristoylphosphatidylcholine (Myr2PtdCho)-based liposomes. The lateral mobility of this derivative, as well as that of N-(4-nitrobenzo-2-oxa-1,3-diazole)phosphatidylethanolamine (NBD-PtdEtn), was measured by fluorescence recovery after photobleaching techniques. In Myr2PtdCho liposomes, the diffusion coefficients (D) of the two probes are the same within experimental error below (D, approximately equal to 2 X 10(-10) cm2 X sec-1) and above (D, approximately equal to 2 X 10(-8) cm2 X sec-1) the main phase transition temperature of the bulk lipid (Tm). There is, however, a distinct difference between the mobilities of the derivatives at concentrations of added cholesterol between 5 and 20 mol % at temperatures below the main phase transition. Under these conditions, the diffusion coefficient of NBD-Chol is approximately twice that of NBD-PtdCho, a result consistent with the idea that cholesterol undergoes a lateral phase separation in these membranes at concentrations less than 20 mol %. At cholesterol concentrations greater than 20 mol % or temperatures above the Tm, the D values of the two probes are identical. The lateral mobility of a cholesterol derivative has thus been monitored directly in cholesterol-containing membranes.

Teleconference and videotape as teaching tools for multi-university instruction.

The combination of several existing technologies and application of them in a regional inter-university series of training programs is described. Using teleconference and videotape, the Central Conference of University Training Programs in Developmental Disabilities has provided its 15 member centers with a set of training materials that would be unavailable to them on an individual basis. Six program series have been produced and a seventh is being planned. The developmental process and the techniques employed are discussed.

Lateral mobility of band 3 in the human erythrocyte membrane studied by fluorescence photobleaching recovery: evidence for control by cytoskeletal interactions.

Band 3, the major intrinsic protein of the human erythrocyte membrane, was specifically labeled with the covalent fluorescent probe eosin isothiocyanate. The lateral mobility of labeled band 3 in the plane of the membrane under various conditions of ionic strength and temperature was examined by using the fluorescence photobleaching recovery technique. Low temperature (21 degrees C) and high ionic strength (46 mM NaPO(4)) favored immobilization of band 3(10% mobile) as well as slow diffusion of the mobile fraction (diffusion coefficient D = 4 x 10(-11) cm(2)sec(-1)). Increasing temperature (37 degrees C) and decreasing ionic strength (13 mM NaPO(4)) led to an increase in the fraction of mobile band 3(90% mobile) and a reversible increase in the diffusion rate of the mobile fraction (D = 200 x 10(-11) cm(2)sec(-1)). The increase in the fraction of mobile band 3 was markedly dissociated, however, from the increase in the diffusion rate of the mobile fraction. Thus, the fraction of mobile band 3 always increased at higher ionic strength and lower temperature than the ionic strength and temperature at which the diffusion rate increased. This dissociation was manifested kinetically on prolonged incubation of ghosts at constant ionic strength and temperature: the diffusion rate of the mobile fraction increased slowly at first and much more rapidly after the initial lag period, whereas the fraction of mobile band 3 increased almost immediately to 90% and remained maximal for the duration of the experiment. Further, changes in diffusion rate with temperature were promptly and totally reversible, whereas increases in the mobile fraction were only slowly and partially reversible. These effects were shown not to be due to complete dissociation of spectrin, the major protein of the erythrocyte cytoskeleton, from the membrane. This evidence suggests control of band 3 lateral mobility by at least two separate processes. The process that determines the diffusion coefficient of the mobile band 3 is completely reversible, and it probably involves a metastable state of cytoskeleton structure intermediate between tight binding to the membrane and complete dissociation from it.

The urethral chain: a simplified approach to chain cystourethrography.

A new urethral chain for simplified chain cystourethrography is presented. The device consists of a series of beads threaded on a fine chain, and is inserted without the use of a catheter. No complications have been encountered to date.

Comparison of the effect of linear gramicidin analogues on bacterial sporulation, membrane permeability, and ribonucleic acid polymerase.

Various analogues of linear gramicidin were tested for their biological activity in restoring the normal spore phenotype of gramicidin-negative mutants of Bacillus brevis and for their ability to increase cation conductivity of black lipid membranes and to inhibit bacterial RNA polymerase. Whereas many biologically active gramicidin analogues had no effect on membrane permeability, all biologically active peptides were able to inhibit ribonucleic acid (RNA) polymerase. These observations make it unlikely that membranes are the site of action of gramicidin during bacterial sporulation, but they are consistent with the notion that gramicidin functions to control RNA synthesis during the transition from vegetative growth to sporulation (Sarkar & Paulus, 1972). The relationship between peptide structure and the ability to restore normal sporulation and inhibit RNA polymerase showed that the eight amino-terminal residues have little influence on the function of gramicidin, whereas the highly nonpolar repeating sequence D-leucyl-L-tryptophan is essential for biological activity and may represent the site of interaction with RNA polymerase.

Conformation of gramicidin A channel in phospholipid vesicles: a 13C and 19F nuclear magnetic resonance study.

We have determined the conformation of the channel-forming polypeptide antibiotic gramicidin A in phosphatidylcholine vesicles by using 13C and 19F NMR spectroscopy. The models previously proposed for the conformation of the dimer channel differ in the surface localization of the NH2 and COOH termini. We have incorporated specific 13C and 19F nuclei at both the NH2, and COOH termini of gramicidin and have used 13C and 19F chemical shifts and spin lattice relaxation time measurements to determine the accessibility of these labels to three paramagnetic NMR probes--two in aqueous solution and one attached to the phosphatidylcholine fatty acid chain9 all of our results indicate that the COOH terminus of gramicidin in the channel is located near the surface of the membrane and the NH2 terminus is buried deep within the lipid bilayer. These findings strongly favor an NH2-terminal to NH2-terminal helical dimer as the major conformation for the gramicidin channel in phosphatidylcholine vesicles.

Preparation and properties of O-dansyltyrosine gramicidin C.

Gramicidins A, B, and C are a family of poly-peptide antibiotics which facilitate the passive diffusion of alkali cations and protons through lipid bilayer membranes. It is clear that gramicidin forms a multimeric transmembrane channel and it has been suggested that the channel is an io-conducting dimer in equilibrium on the membrane with non-conducting monomer. We describe the preparation and purification of a derivative of gramicidin C in which the phenolic hydroxyl of the tyrosine at position 11 has been esterified to 8-dimethylaminonaphthalene-1-sulfonate (dansyl). This derivative fluoresces strongly in the visible with an emission maximun in dioxane of 530 nm, an emission lifetime of 16 ns, and a quantum yield of 0.8. Veatch et al. ((1975),J. Mol. Biol. 99, 75) have shown this 0-dansyltyrosine gamicidin C to be a fully active analogue of gramicidin A in artificial lipid bilayer membranes. We here utilize this derivative to further characterize the state of aggregation and rotational mobility of the four interconvertible conformational species formed by gramicidin in nonpolar organic solvents (Veatch et al. (1974), Biochemsitry 13, 5249; Veatch and Blout (1974), Biochemistry 13, 5257). Fluorescence energy transfer from the tryptophans of gramicidin A to the 0-dansyltyrosine of this derivatives supports the conclusion that all of these gramicidin isolated species are aggregates. Decay of fluorescence polarization anisotropy measurements yield a rotational correlation time of 1 ns for the 0-dansyltyrosine chromophore in ethanol in good agreement with the more detailed information previously obtained by 13C-nuclear magnetic resonance for the monomer in dimethyl sulfoxide (Fossel et al. (1974), Biochemistry 13, 5264). However, it is likely that the chromophore has much more rotational mobility than the rest of the gramicidin molecule in the aggregated comformational states.