Triton's Geyser-Like Plumes: Discovery and Basic Characterization

At least four active geyser-like eruptions were discovered in Voyager 2 images of Triton, Neptune's large satellite. The two best documented eruptions occur as columns of dark material rising to an altitude of about 8 kilometers where dark clouds of material are left suspended to drift downwind over 100 kilometers. The radii of the rising columns appear to be in the range of several tens of meters to a kilometer. One model for the mechanism to drive the plumes involves heating of nitrogen ice in a subsurface greenhouse environment; nitrogen gas pressurized by the solar heating explosively vents to the surface carrying clouds of ice and dark partides into the atmosphere. A temperature increase of less than 4 kelvins above the ambient surface value of 38 +/- 3 kelvins is more than adequate to drive the plumes to an 8-kilometer altitude. The mass flux in the trailing clouds is estimated to consist of up to 10 kilograms of fine dark particles per second or twice as much nitrogen ice and perhaps several hundred or more kilograms of nitrogen gas per second. Each eruption may last a year or more, during which on the order of a tenth of a cubic kilometer of ice is sublimed.     

Amino acid transport in hepatoma cell cultures during tyrosine aminotransferase induction

Alpha-aminoisobutyric acid transport in hepatoma cells in culture was increased by insulin but not by hydrocortisone. Both of these agents induce tyrosine aminotransferase activity in this system. The apparent increase in alpha-aminoisobutyric acid transport and tyrosine aminotransferase activity produced by glucagon is probably caused by insulin contamination. Insulin did not increase transport in this system until after tyrosine aminotransferase activity had reached maximum levels. The mechanisms underlying increased alpha-aminoisobutyric acid transport appear to differ from those for tyrosine aminotransferase induction with hydrocortisone despite their close association in previous whole animal experiments.     

Substitution of the thioredoxin system for glutathione reductase in Drosophila melanogaster

The disulfide reducing enzymes glutathione reductase and thioredoxin reductase are highly conserved among bacteria, fungi, worms, and mammals. These proteins maintain intracellular redox homeostasis to protect the organism from oxidative damage. Here we demonstrate the absence of glutathione reductase in Drosophila melanogaster, identify a new type of thioredoxin reductase, and provide evidence that a thioredoxin system supports GSSG reduction. Our data suggest that antioxidant defense in Drosophila, and probably in related insects, differs fundamentally from that in other organisms.