The effects of ionophores and metabolic inhibitors on methanogenesis and energy-related properties of Methanobacterium bryantii

The effects of numerous ionophores and inhibitors were tested on methane synthesis, intracellular ATP and potassium concentrations, and the proton motive force of the methanogenic archaebacterium Methanobacterium bryantii. M. bryantii had an internal pH near 6.8 (and hence little ΔpH during growth) with an electrical potential of ?127 mV in growth medium and ?105 mV in a pH 6.5 buffer. The study has identified agents which, in M. bryantii, can effectively cause a decline of intracellular ATP (gramicidin, acetylene) and potassium concentrations (gramicidin, nigericin), inhibit methane synthesis (acetylene, gramicidin, nigericin, triphenylmethylphosphonium bromide), eliminate the electrical potential (high extracellular potassium ion concentrations), and dissipate artificially imposed, inside alkaline, pH gradients (monensin, nigericin, carbonyl cyanide m-chlorophenylhydrazone). Carbonyl cyanide m-chlorophenylhydrazone was generally ineffective in media or buffers reduced with cysteine-sulfide but could be effective in cysteine-free solutions reduced with hydrogen sulfide.     

Cloning and orientation of the gene encoding polynucleotide phosphorylase in Escherichia coli.

Mutations which affect the activity of polynucleotide phosphorylase (PNPase) map near 69 min on the bacterial chromosome. This region of the chromosome has been cloned by inserting the kanamycin-resistant transposon Tn5 near the argG and mtr loci at 68.5 min. Large SalI fragments of chromosomal DNA containing the Tn5 element were inserted into pBR322, and selection was made for kanamycin-resistant recombinant plasmids. Two of these plasmids were found to produce high levels of PNPase activity in both wild-type and host strains lacking PNPase activity. The pnp gene was further localized and subcloned on a 4.8 kilobase HindIII-EcoRI fragment. This fragment was shown to encode an 84,000-molecular weight protein which comigrated with purified PNPase during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The orientation of the pnp gene was determined by insertion of Tn5 into the 4.8 kilobase fragment cloned in pBR322. Some of the insertions had lost the ability to elevate the level of PNPase activity in the host bacterium. Restriction mapping of the positions of the Tn5 insertions and analysis of plasmid-encoded polypeptides in UV-irradiated maxi-cells indicated that the pnp gene is oriented in the counterclockwise direction on the bacterial chromosome.     

Skeletal growth in a medieval population from Sudanese Nubia

Long bone growth is analyzed for 180 children from a Medieval population at Kulubnarti in Sudanese Nubia (550–1450 A.D.). A regional interpopulation comparison is made with growth data from Wadi Halfa in Lower Nubia, and an intrapopulation analysis is undertaken to assess diachronic changes in growth at Kulubnarti. Changes in growth patterns are interpreted in the context of mortality and morbidity profiles and relationships between the three variables are discussed. It is suggested that changes in the sociopolitical environment may have been responsible in part for altering levels of biological stress and impacting growth.     

Solubilization of phospholipids by detergents. Structural and kinetic aspects

Most amphiphiles in biological membranes including phospholipids, steroids, and membrane proteins are insoluble amphiphiles and would form liquid crystals or insoluble precipitates alone in aqueous media. Detergents are soluble amphiphiles and above a critical concentration and temperature form micelles of various sizes and shapes. Much of the recent progress in studying the insoluble amphiphiles is due to the formation of thermodynamically stable isotropic solutions of these compounds in the presence of detergents. This process, which is commonly denoted as "solubilization,' involves transformation of lamellar structures into mixed micelles. The information available to date on the solubilization of phospholipids, which constitute the lipid skeleton of biomembranes, by the common detergents is discussed in this review, both with respect to the kinetics of this process and the structure of the various phospholipid-detergent mixed micelles formed. It is hoped that this discussion will lead to somewhat more useful, although still necessarily fairly empirical, approaches to the solubilization of phospholipids by detergents.     

Significance of the delta 5 and delta 4 steroidogenic pathways in the hamster preovulatory follicle

Isolated hamster granulosa cells and theca from preovulatory follicles were incubated in vitro for 2 and 6 h in the absence/or presence of LH and steroid substrates. The purpose of the experiments was to determine, in theca, the relative activities of the delta 5 and delta 4 pathways under controlled conditions, and to compare the ability of granulosa cells and theca to form progesterone from exogenous pregnenolone. The results of the experiments show that the delta 5 pathway in theca predominates before and up to 2 h after LH stimulation. The delayed effect of LH after 2 h is a switch from delta 5 to delta 4 as the major metabolic pathway. Progesterone formation from exogenous pregnenolone is 7 to 10 times greater in unstimulated granulosa cells than in theca. Acute effects of LH lead to increased conversion of exogenous pregnenolone to progesterone in granulosa cells but not theca. LH does, however, acutely stimulate the thecal conversion of DHEA to androstenedione. The longer term effect of LH in both cell types is to increase pregnenolone conversion to progesterone.     

Structural and functional studies of the adrenal zona glomerulosa in sodium-depleted and sodium-loaded sheep

Cell and Tissue Research - The effects of alterations in sodium status upon the morphology of the adrenal zona glomerulosa in sheep have been examined qualitatively and quantitatively, using...     

FREE-FLOW ELECTROPHORETIC SEPARATION AND ELECTRICAL SURFACE PROPERTIES OF SUBCELLULAR PARTICLES FROM GUINEA PIG BRAIN

Continuous free-flow electrophoretic separation has been used to obtain relatively pure preparations of synaptosomes and synaptic vesicles from crude fractions of guinea pig brain homogenates. Measurements of the contents of protein, neuraminic acid, and bound acetylcholine; the activities of succinic dehydrogenase, adenosine triphosphatase, choline acetylase, and 5'-nucleotidase; and the uptake of ¹⁴C-labeled choline arid acetylcholine in the presence and absence of hemicholinium, all confirm the electron microscope evidence that the electrophoretic preparations are at least as pure as those obtained by ultracentrifugal methods. The electrophoretic mobility measurements have been used to calculate zeta potentials and surface charge densities for these particles.