Melvin P. Silverman

Relationship between proton motive force and potassium ion transport in Halobacterium halobium envelope vesicles

Abstract Membrane vesicles prepared from Halobacterium halobium extrude protons during illumination, and a pH difference (inside alkaline) and an electrical potential (inside negative) develop. The sizes of these gradients and their relative magnitudes are dependent on a complex interaction among the proton-pumping activity of bacteriorhodopsin, Na+ extrusion through an antiport system, and the ability of K+ and Cl− to act as counterions to the electrogenic movement of H+. The net result of these variable effects is that the electrical potential is relatively independent of external pH, whereas the pH difference tends toward zero when the pH is increased to 7.5–8. Although the light-induced pH difference is greater in KCl than in NaCl, and the electrical potential smaller, this is not caused by a high permeability of the vesicle membranes to K+. The vesicle membrane is poorly permeable to K+, as shown by: lack of a K+ diffusion potential in the absence of valinomycin, light-induced electrical potentials which are in excess of the chemical potential difference for K+, and direct measurements of the slow rate of K+ influx during illumination. The finding that the rate of K+ uptake is a linear function of external K+ concentration between 0 and 1 m is inconsistent with the existence of a specific K+ permeation mechanism in these vesicles. Since at external K+ concentrations m the extrusion of Na+ during illumination proceeds much more rapidly than K+ influx, it must be concluded that the vesicles also lose Cl− and water. Measurements of light-scattering changes confirm that under these conditions the vesicles collapse. The light-induced collapse is diminished only when the inward movement of K+ is increased, either by increasing the external K+ concentration or by adding valinomycin.

A Search for Viable Organisms in a Lunar Sample

The hypothesis that the moon could harbor viable life forms was not verified on analysis of the first samnples from the Apollo 11 mission. Biological examnination of 50 grainis of the butlk fines confirmn the negative results obtained by the Manned Spacecraft Center quarantine teamyz. No viable life forms, including terrestrial contaminants, were found when the sample was tested in 300 separate environmtenits. Only colored illorganiic artifacts, resembling mnicrobial clonies, appeared aroun1cd some particles. Manned Spacecraft Center, Houston.

Water soluble cations and the fluvial history of mars

Abstract The electrical conductivity and water soluble Na, K, Ca, and Mg of aqueous solutions of terrestrial soils and finely divided igneous and metamorphic rocks were determined. Soils from dry terrestrial basins with a history of water accumulation as well as soils from the topographic lows of valleys accumulated water soluble cations, particularly Na and Ca. These soils as a group can be distinguished from the rocks or a second group of soils (leached upland soils and soils from sites other than the topographic lows of valleys) by significant differences in their mean electrical conductivity and water soluble Na + Ca content. Similar measurements on multiple samples from the surface of Mars, collected by an automated long-range roving vehicle along a highlands to basin transect at sites with morphological features resembling dry riverlike channels, are suggested to determine the fluvial history of the planet.