Nucleic acid relationships among Acholeplasma species.

3H-labeled Acholeplasma DNA probes were generated in vitro by the nick-translation method and used to determine the nucleotide sequence homology among the type strains of the eight currently recognized species of Acholeplasma. Very little nucleotide sequence homology (less than or equal to 18%) was found among the eight species, with heteroduplexes showing at least 12% or more mismatching as determined by thermal elution midpoints. The small amount of nucleotide sequence homology among the eight species indicates that these species are quite distinct and are not closely related to each other genomically.     

Free and polymerized tubulin in cultured bone cells and Chinese hamster ovary cells: the influence of cold and hormones

A low pH method of liposome-membrane fusion (Schneider et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:442) was used to enrich the mitochondrial inner membrane lipid bilayer 30-700% with exogenous phospholipid and cholesterol. By varying the phospholipid-to- cholesterol ratio of the liposomes it was possible to incorporate specific amounts of cholesterol (up to 44 mol %) into the inner membrane bilayer in a controlled fashion. The membrane surface area increased proportionally to the increase in total membrane bilayer lipid. Inner membrane enriched with phospholipid only, or with phospholipid plus cholesterol up to 20 mol %, showed randomly distributed intramembrane particles (integral proteins) in the membrane plane, and the average distance between intramembrane particles increased proportionally to the amount of newly incorporated lipid. Membranes containing between 20 and 27 mol % cholesterol exhibited small clusters of intramembrane particles while cholesterol contents above 27 mol % resulted in larger aggregations of intramembrane particles. In phospholipid-enriched membranes with randomly dispersed intramembrane particles, electron transfer activities from NADH- and succinate-dehydrogenase to cytochrome c decreased proportionally to the increase in distance between the particles. In contrast, these electron- transfer activities increased with decreasing distances between intramembrane particles brought about by cholesterol incorporation. These results indicate that (a) catalytically interacting redox components in the mitochondrial inner membrane such as the dehydrogenase complexes, ubiquinone, and heme proteins are independent, laterally diffusible components; (b) the average distance between these redox components is effected by the available surface area of the membrane lipid bilayer; and (c) the distance over which redox components diffuse before collision and electron transfer mediates the rate of such transfer.     

Food sharing: a model of manipulation by harassment

Most analyses of food-sharing behavior invoke complex explanationssuch as indirect and delayed benefits for sharing via kin selectionand reciprocal altruism. However, food sharing can be a moregeneral phenomenon accounted for by more parsimonious, mutualisticexplanations. We propose a game theoretical model of a generalsharing situation in which food owners share because it is in their own self-interest—they avoid high costs associatedwith beggar harassment. When beggars harass, owners may benefitfrom sharing part of the food if their consumption rate islow relative to the rate of cost accrual. Our model predictsthat harassment can be a profitable strategy for beggars if they reap some direct benefits from harassing other than sharedfood (such as picking up scraps). Therefore, beggars may manipulatethe owner's fitness payoffs in such a way as to make sharingmutualistic.     

Ultrastructural changes in isolated rat hepatocytes exposed to different CCl4 concentrations

Ultrastructural data are presented on time-course changes in isolated rat hepatocyte suspensions exposed either to 1.2 or 1.8 mM CCl4 for up to 1 h. The subcellular changes at the lower concentration, but not the higher, are shown to closely parallel those reported to occur in rat hepatocytes following ingestion of CCl4.     

Epidermal capillariasis in South African clawed frogs (Xenopus laevis)

Significant morbidity and mortality of South African clawed frogs, Xenopus laevis, can be caused by parasitism of the epidermis by a capillarid nematode. These worms produce an erosive dermatitis that is complicated by infection with gram-negative microorganisms. The nematode apparently has a direct life cycle that can be completed within the epidermis of the frog. These characteristics are suggested by the lack of an intermediate host and failure to detect visceral migration. Another unique feature of the parasite was the presence of larvated eggs, in utero. Some have named the parasite Capillaria xenopodis, whereas others called it Pseudocapillaroides xenopi to distinguish it form the typical members of the genus Capillaria.     

Active Uptake of Amino Acids by Leaves of an Epiphytic Vascular Plant, Tillandsia paucifolia (Bromeliaceae)

Specialized epidermal trichomes on the leaves of the epiphyte, Tillandsia paucifolia (Bromeliaceae) accumulate amino acids from solution. Simultaneous net uptake of 17 amino acids was determined using high performance liquid chromatography. Uptake occurs against concentration gradients at least as high as 10⁴.     

Multiple metabolic pools of phosphoinositides and phosphatidate in human erythrocytes incubated in a medium that permits rapid transmembrane exchange of phosphate.

1. A Hepes-based medium has been devised which allows rapid Pi exchange across the plasma membrane of the human erythrocyte. This allows the metabolically labile phosphate pools of human erythrocytes to come to equilibrium with [32P]Pi in the medium after only 5 h in vitro. 2. After 5-7 h incubation with [32P]Pi in this medium, only three phospholipids, phosphatidic acid (PtdOH), phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2) are radioactively labelled. The concentrations of PtdIns4P and PtdIns4,5P2 remain constant throughout the incubation, so this labelling process is a reflection of the steady-state turnover of their monoester phosphate groups. 3. During such incubations, the specific radioactivities of the monoesterified phosphates of PtdIns4, PtdIns4,5P2 and PtdOH come to a steady value after 5 h that is only 25-30% of the specific radioactivity of the gamma-phosphate of ATP at that time. We suggest that this is a consequence of metabolic heterogeneity. This heterogeneity is not a result of the heterogeneous age distribution of the erythrocytes in human blood. Thus it appears that there is metabolic compartmentation of these lipids within cells, such that within a time-scale of a few hours only 25-30% of these three lipids are actively metabolized. 4. The phosphoinositidase C of intact human erythrocytes, when activated by Ca2+-ionophore treatment, only hydrolyses 50% of the total PtdIns4,5P2 and 50% of 32P-labelled PtdIns4,5P2 present in the cells: this enzyme does not discriminate between the metabolically active and inactive compartments of lipids in the erythrocyte membrane. Hence at least four metabolic pools of PtdIns4P and PtdIns4,5P2 are distinguishable in the human erythrocyte plasma membrane. 5. The mechanisms by which multiple non-mixing metabolic pools of PtdOH, PtdIns4P and PtdIns4,5P2 are sustained over many hours in the plasma membranes of intact erythrocytes are unknown, although some possible explanations are considered.     

Turkey erythrocyte membranes as a model for regulation of phospholipase C by guanine nucleotides

Phosphoinositides of human, rabbit, rat, and turkey erythrocytes were radiolabeled by incubation of intact cells with [32P]Pi. Guanosine 5'-O-(thiotriphosphate) (GTP gamma S) and NaF, which are known activators of guanine nucleotide regulatory proteins, caused a large increase in [32P]inositol phosphate release from plasma membranes derived from turkey erythrocytes, but had no effect on inositol phosphate formation by plasma membranes prepared from the mammalian erythrocytes. High performance liquid chromatography analysis indicated that inositol bisphosphate, inositol 1,3,4-trisphosphate, inositol 1,4,5-trisphosphate, and inositol 1,3,4,5-tetrakisphosphate all increased by 20-30-fold during a 10-min incubation of turkey erythrocyte membranes with GTP gamma S. The increase in inositol phosphate formation was accompanied by a similar decrease in radioactivity in phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2). GTP gamma S increased inositol phosphate formation with a K0.5 of 600 nM; guanosine 5'-(beta, gamma-imido)trisphosphate was 50-75% as efficacious as GTP gamma S and expressed a K0.5 of 36 microM. Although GTP alone had little effect on inositol phosphate formation, it blocked GTP gamma S-stimulated inositol phosphate formation, as did guanosine 5'-O-(2-thiodiphosphate). Turkey erythrocytes were also shown to express phosphatidylinositol synthetase activity in that incubation of cells with [3H] inositol resulted in incorporation of radiolabel into phosphatidylinositol, PIP, and PIP2. Incubation of membranes derived from [3H]inositol-labeled erythrocytes with GTP gamma S resulted in large increases in [3H] inositol phosphate formation and corresponding decreases in radiolabel in PIP and PIP2. The data suggest that, in contrast to mammalian erythrocytes, the turkey erythrocyte expresses a guanine nucleotide-binding protein that regulates phospholipase C, and as such, should provide a useful model system for furthering our understanding of hormonal regulation of this enzyme.