Cardiac dysfunction in patients seropositive for the human immunodeficiency virus.

To confirm the presence of cardiac dysfunction in a group of patients seropositive for the human immunodeficiency virus with either dyspnea on exertion or a reduced anaerobic threshold, 9 patients with no history of opportunistic infection underwent exercise right-sided heart catheterization. When compared with 13 control patients previously exercised in the same manner, the patients showed elevated exercise pulmonary capillary wedge pressure (14.6 +/- 3.3 mm of mercury versus 9.9 +/- 3.3 mm of mercury; P less than .005) and right atrial pressure (10.1 +/- 2.1 mm of mercury versus 4.7 +/- 3.2 mm of mercury; P less than .001) at a similar exercise oxygen consumption and cardiac index. Of the 9 patients, 8 had at least 1 catheterization value outside the 95% confidence limits for the control group and 4 patients had multiple abnormalities. Values for blood CD4 lymphocytes were 0.2 x 10(9) per liter or more for 7 of the 9. One patient underwent endomyocardial biopsy with findings consistent with a cardiomyopathy. We conclude that cardiac disease may occur at any immunologic stage of human immunodeficiency virus infection. These observations suggest an effect of this disease on the heart.     

Localization of a liver transglutaminase and a large molecular weight transglutaminase substrate to a distinct plasma membrane domain

Rat liver plasma membranes contain transglutaminase activity and a large molecular weight protein aggregate that serves as a substrate for this enzyme (Slife, C.W., Dorsett, M.D., Bouquett, G.T., Register, A., Taylor, E., and Conroy, S. (1985) Arch. Biochem. Biophys. 241, 329-336; Slife, C.W., Dorsett, M.D., and Tillotson, M.L. (1986) J. Biol. Chem. 261, 3451-3456). When purified plasma membranes were sonicated and the different plasma membrane domains were separated by sedimentation through a linear sucrose gradient, virtually all of the transglutaminase activity and the large molecular weight transglutaminase substrate were associated with membrane fragments which migrated to a very dense region of the gradient (1.18 g/cm3). The bile canalicular markers, 5'-nucleotidase and HA-4 antigen, were predominantly found at 1.11 g/cm3, while most of the sinusoidal/lateral marker, CE-9 antigen, was detected at 1.14 g/cm3. Smooth membrane vesicles were observed chiefly at the lighter densities upon morphological analysis, while many filament-bearing, plasma membrane segments and junctional complexes were contained in the heavy transglutaminase fractions. These data show that the plasma membrane transglutaminase and the large molecular weight transglutaminase substrate are associated with a distinct region of the plasma membrane.     

Tsc3p is an 80-amino acid protein associated with serine palmitoyltransferase and required for optimal enzyme activity

Serine palmitoyltransferase catalyzes the first step of sphingolipid synthesis, condensation of serine and palmitoyl CoA to form the long chain base 3-ketosphinganine. The LCB1/TSC2 and LCB2/TSC1 genes encode homologous proteins of the alpha-oxoamine synthase family required for serine palmitoyltransferase activity. The other alpha-oxoamine synthases are soluble homodimers, but serine palmitoyltransferase is a membrane-associated enzyme composed of at least two subunits, Lcb1p and Lcb2p. Here, we report the characterization of a third gene, TSC3, required for optimal 3-ketosphinganine synthesis in Saccharomyces cerevisiae. S. cerevisiae cells lacking the TSC3 gene have a temperature-sensitive lethal phenotype that is reversed by supplying 3-ketosphinganine, dihydrosphingosine, or phytosphingosine in the growth medium. The tsc3 mutant cells have severely reduced serine palmitoyltransferase activity. The TSC3 gene encodes a novel 80-amino acid protein with a predominantly hydrophilic amino-terminal half and a hydrophobic carboxyl terminus that is membrane-associated. Tsc3p coimmunoprecipitates with Lcb1p and/or Lcb2p but does not bind as tightly as Lcb1p and Lcb2p bind to each other. Lcb1p and Lcb2p remain tightly associated with each other and localize to the membrane in cells lacking Tsc3p. However, Lcb2p is unstable in cells lacking Lcb1p and vice versa.     

Effect of glyphosate on carrot and tobacco cells

The growth of suspension-cultured carrot (Daucus carota L.) and tobacco (Nicotiana tabacum L. cv. Xanthi) cells was inhibited by glyphosate (N-[phosphonomethyl]glycine). This inhibition was reversed by adding combinations of phenylalanine, tyrosine, and tryptophan or casein hydrolysate. Casein hydrolysate and phenylalanine + tyrosine + tryptophan were the most effective treatments. Reversal of glyphosate-induced inhibition occurred only if the aromatic amino acids were added during the first 8 days of glyphosate incubation. Glyphosate uptake was not reduced when the aromatic amino acids or casein hydrolysate were added.     

Subcellular location and identification of a large molecular weight substrate for the liver plasma membrane transglutaminase

When the particulate fraction from a rat liver homogenate was incubated with [3H]putrescine and calcium, the radioactive amine was incorporated into the membranes via a transglutaminase-mediated reaction. Fractionation of the membranes by isopycnic density gradient centrifugation revealed that the radioactive label was coincident with the 5'-nucleotidase and transglutaminase activities which serve as markers for the plasma membrane (Slife, C. W., Dorsett, M. D., Bouquett, G. T., Register, A., Taylor, E., and Conroy, S. Arch. Biochem. Biophys. 241, 329-336). If the labeled membranes were treated with digitonin and fractionated, the radioactivity and the plasma membrane enzyme activities coincidentally shifted to a greater density. Examination of the [3H]putrescine-labeled membranes by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography showed that the largest amount of radioactivity was associated with a large molecular weight material that did not enter the acrylamide gel. Pulse-chase experiments indicated that the large aggregate already was present in the native membrane, or that it was formed very rapidly during the putrescine incubation. The complex did not result from putrescine cross-linking between proteins since dansylcadaverine and [3H]histamine were also selectively incorporated into it. These data show that there are protein substrates in the plasma membrane which are accessible to the membrane-associated transglutaminase and that the substrates form a large molecular weight aggregate which is not dissociated by sodium dodecyl sulfate and disulfide reducing agents.     

Effects of aspartate and other compounds on glyphosate uptake and growth inhibition in cultured carrot cells

The strong correlation between glyphosate uptake and growth inhibition of cultured carrot (Daucus carota L. cv Danvers) cells incubated in the presence of aspartate suggests that aspartate reverses glyphosate inhibition of growth primarily by reducing intracellular glyphosate concentration. Other compounds which reverse glyphosate inhibition of cell growth gave a range of effects on glyphosate uptake: succinate, α-ketoglutarate, glutamate, pyruvate, and malate at 10 millimolar and phenylalanine at 2 millimolar reduced uptake by 0, 8, 11, 16, 27, and 34%, respectively. These results suggest that more than one mechanism of reversal may operate in these cells.

Glyphosate and aspartate produced only minor effects on intracellular ammonia, media pH, and cell viability. This suggests that ammonia toxicity may not be an important mechanism of action of glyphosate in this system.