Respiration-driven proton translocation in Thiobacillus versutus and the role of the periplasmic thiosulphate-oxidizing enzyme system

The periplasmic location of enzymes A and B of the thiosulphate-oxidizing multienzyme system of Thiobacillus versutus has been further confirmed by differential radiolabelling of periplasmic and cytoplasmic proteins. The stoichiometries of respiration-driven proton translocation in T. versutus were determined using the oxygen pulse and the initial rate methods. A value for the H⁺/O quotient (number of protons translocated per oxygen atom reduced) of about 2.8 was found for the oxidation of thiosulphate, and of about 2.5 for sulphite. The H⁺/O quotient for endogenous respiration was about 5.7. The data are shown to be in good agreement with the scheme proposed previously for thiosulphate oxidation by this organism. Proton generation during the oxidation of thiosulphate or sulphite is indicated to occur in the periplasm rather than by pumping across the cytoplasmic membrane. The results also suggest that a H⁺/O quotient of six occurs during NADH oxidation (from endogenous metabolism measurements) and that the terminal cytochrome oxidase, aa₃, does not function as a proton pump.Abbreviations DCCD dicyclohexyl carbodiimide - FCCP carbonyl cyanide p-trifluoromethoxyphenylhydrazone - HQNO 2-n-heptyl-4-hydroxyquinoline N-oxide - TMPD N,N,N,N-tetramethyl-p-phenylenediamine - IEF isoelectric focusing - HIC hydrophobic interaction chromatography - EAI ethyl acetimidate hydrochloride - IAI isethionyl acetimidate     

The genetic structure of a primate species: Rhesus macaques and other Cercopithecine monkeys

Among rhesus macaques (Macaca mulatta)and other cercopithecine monkeys, social groups occupying adjacent home ranges (i.e., members of the same local population) exchange individuals and genes and thus exhibit marked genetic similarities. To assess the degree to which this pattern extends beyond the local population, the genetic structure of M. mulattaand six other primate species was determined using Nei’s (1973) gene-diversity analysis. The genetic similarities seen among social groups in the Dunga Gali population of M. mulatta (Melnick et al.,1984a) can be seen over the entire species range. Comparison of these results with the structures of other similarly organized primate species indicates that (1) the average social group contains most of its local population’s genetic diversity, (2) the average local population contains the majority of the genetic diversity found in the region to which it belongs, and (3) the proportion of species gene diversity found in the average regional population varies substantially between species. Genetic homogeneity within local and regional populations is probably the product of gene flow. The application of a number of analytical models of selection and gene flow strongly suggests that gene flow, genetic drift, and zoogeography offer a more parsimonious and plausible explanation for interspecific variation in regional differentiation than does stabilizing selection.     

Age Structure and Community Diversity of Nematodes Associated with Maize in Iowa Sandy Soils

Age structure of nematode populations around maize growing in sandy soils in Iowa was studied at soil depths of 0-15and 15-30 cm for 2 years. Numbers of Longidorus breviannulatus were generally greater at 0-15 cm than at 15-30 cm deep until mid to late season. The decline in numbers of females as the season progressed indicates that fecundity slowed and is evidence of only one generation per year. Peak populations of Pratylenchus scribneri and Xiphinema americanum occurred in late August or early September. Adults of Hoplolaimus galeatus were few in the roots but common in the soil, indicating that fertilization occurred mostly in the soil. Numbers of P. scribneri were generally greater at the lower depth, especially late in the season. Community diversity (H'') was less when nematode biomass was used instead of numbers. Numbers of H. galeatus did not decline over the winter. Numbers of L. breviannulatus, P. scribneri, and X. americanum declined significantly over the winter, but not between spring cultivation and planting.     

Gradients of Intercellular CO(2) Levels Across the Leaf Mesophyll

Most current photosynthesis models, and interpretations of many wholeleaf CO₂ gas exchange measurements, are based on the often unstated assumption that the partial pressure of CO₂ is nearly uniform throughout the airspaces of the leaf mesophyll. Here we present measurements of CO₂ gradients across amphistomatous leaves allowed to assimilate CO₂ through only one surface, thus simulating hypostomatous leaves. We studied five species: Eucalyptus pauciflora Sieb. ex Spreng., Brassica chinensis L., Gossypium hirsutum L., Phaseolus vulgaris L., and Spinacia oleracea L. For Eucalyptus, maximum CO₂ pressure differences across the leaf mesophyll were 73 and 160 microbar when the pressures outside the lower leaf surface were 310 and 590 microbar, respectively. Using an approximate theoretical calculation, we infer that if the CO₂ had been supplied equally at both surfaces then the respective mean intercellular CO₂ pressures would have been roughly 12 and 27 microbar less than the pressures in the substomatal cavities in these cases. For ambient CO₂ pressures near 320 microbar, the average and minimum pressure differences across the mesophyll were 45 and 13 microbar. The corresponding mean intercellular CO₂ pressures would then be roughly 8 and 2 microbar less than those in the substomatal cavities. Pressure differences were generally smaller for the four agricultural species than for Eucalyptus, but they were nevertheless larger than previously reported values.     

Tubulin isotypes and their interaction with microtubule associated proteins

Summary To assay the functional significance of the multiple but closely related - and -tubulin polypeptides (termed isotypes) that are expressed in mammalian cells, we have generated a number of sera that uniquely discriminate among these isotypes. These sera have been used to demonstrate that there is no subcellular sorting of either - or -tubulin isotypes among microtubules of diverse function, either in cells growing in culture or in tissues consisting of cell types that contain specialized kinds of microtubule. In spite of this failure to segregate between functionally distinct kinds of microtubule, the fact that isotype-specific amino acid sequences have been strictly conserved over extensive periods of evolutionary time argues persuasively for a functional role for the different tubulin gene products. One possibility is that they are required for specific interactions with microtubule associated proteins (MAPs), and that tubulin isotypes have coevolved with different cell type-specific MAPs with which they must interact. We have tested this hypothesis by examining the distribution of -tubulin isotypes in mammalian cerebellum in relationship to the known patterns of expression of a number of MAPs, and find that these patterns correlate in the case of M 2 and MAP 3, and M 6 and MAP 1 a. These data, plus emerging data based on a structural analysis of tau, MAP 1 b and MAP 2 obtained via sequence determination of cloned cDNAs, are discussed in terms of the possible functional significance of tubulin isotype/MAP interactionsin vivo.     

Attachment and multiplication,morphology and protein production of human fetal primary liver cells cultured in hormonally defined media

In Vitro Cellular &; Developmental Biology - Plant -     

Effects of selective opioid agonists on feline colonic transit.

The mu agonist morphine and the non-specific opioid antagonist naloxone both may accelerate feline colonic transit; the effects of morphine are dose dependent. Kappa and delta receptor function was studied in the present work. Colonic transit of a radionuclide marker instilled into the cecum was quantitated for 6 hr in a crossover study. The delta agonist [D-Pen2,D-pen5]enkephalin (1 mg/kg, i.m.) prolonged the cecum and ascending colon half-emptying time by 337% (P less than 0.05), and delayed the progression of the geometric center over time. The kappa agonist U-50,488 (1 mg/kg, i.m.) had no apparent effect on the cecum and ascending colon, but delayed filling of the descending colon. Loperamide, an antidiarrheal agent, also delayed colonic transit. Thus, selective opioid agonists have both site and functional differences in their effect on feline colonic transit.     

Levels of chromosomally encoded Umu proteins and requirements for in vivo UmuD cleavage

Summary Most of the inducible mutagenesis observed in Escherichia coli after treatment with many DNA damaging agents is dependent upon the products of the umuD,C operon. RecA-mediated proteolytic processing of UmuD yields a carboxyl-terminal fragment (UmuD) that is active for mutagenesis. Processing of UmuD is therefore a critical step in the fixation of mutations. In this paper we have analyzed the requirements for UmuD processing in vivo. Standard immuno-detection assays, coupled with a sensitive chemiluminescence detection assay, have been utilized to probe levels of chromosomally encoded Umu proteins from whole-cell E. coli extracts. We found that the derepression of additional SOS gene products, other than RecA, was not required for UmuD processing. Moreover, efficient cleavage of UmuD was observed only in the presence of elevated levels of activated RecA, suggesting that efficient processing would occur only under conditions of severe DNA damage. Detection of chromosomally encoded Umu proteins has allowed us, for the first time, to measure directly the cellular steady-state levels of these proteins under various SOS inducing conditions. UmuD was present at 180 copies per uninduced cell and was measured at 2400 copies per cell in strains that lacked a functional repressor. Induced levels of UmuC were approximately 12-fold lower than UmuD with 200 molecules per cell. These levels of cellular UmuC protein suggest that it functions through specific protein-DNA or protein-protein interactions, possibly as a lesion recognition protein or by interacting with DNA polymerase III.