Mitochondrial genome in animal cells. Structure, organization, and evolution

In the past decade, the development of new DNA, RNA, and protein technologies has greatly incremented the knowledge about the organization and expression of mitochondrial DNA. The complete base sequence of mitochondrial DNA of several animals is known and many data are rapidly accumulating on the mitochondrial genomes of other systems. Here we discuss the results so far obtained that disclosed unexpected features of mitochondrial genetics. Furthermore, mitochondrial DNA has become established as a powerful tool for evolutionary studies in animals. Evidences are presented demonstrating that the evolution of mitochondrial DNA has proceeded in different ways in the various taxonomic groups. Data on heteroplasmic animals, which demonstrate the rapid evolution of mitochondrial DNA, are also presented.     

VIP and related peptides induce rapid homologous desensitization in the human lymphoma SUP T1 cell line

Incubation of human SUP T1 lymphoblasts with VIP, helodermin and related peptides induced homologous desensitization within 5 min as indicated by: 1) a secondary decrease in cellular cyclic AMP levels, even in the presence of phosphodiesterase inhibitors, 2) a reduced capacity of cells to bind [125I]helodermin, 3) decreased helodermin stimulation of adenylate cyclase activity in membranes, and 4) unaffected NaF- and Gpp[NH]p-stimulated adenylate cyclase activities. The desensitizing ability of all peptides correlated with their efficacy to occupy cell receptors, except for [D-Phe2]VIP, a partial VIP agonist with low intrinsic activity, that did not desensitize.     

Induction of NADP-dependent malic dehydrogenase activity in brain of singi fish, heteropneustes fossilis (bloch), by 3,5,3′-triiodothyronine

For elucidation of thyroid hormone-induced responsiveness of fish brain, various doses (0.012, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2 and 4 μg/g) of triiodothyronine (T₃) were injected in Singi fish, Heteropneustes fossilis (Bloch), for 3 consecutive days and the changes in cytosolic NADP-dependent malic enzyme (ME, EC 1.1.1.40) activity in whole brain tissue were determined. Compared to the control, the ME activity increased with lower doses (0.012, 0.025 and 0.05 μg/g) and decreased with higher doses (1, 2 and 4 μg/g) of T₃, showing a biphasic nature of thyroid hormone action. The enzyme activity remained unaltered with 0.1, 0.25 and 0.5 μg of T₃/g in comparison to the control. Immersion of the fishes in cycloheximide-containing medium (0.5 mg/l) inhibited the T₃ (0.025 μg/g)-induced rise in ME activity. On the other hand, the NAD-dependent cytosolic malate dehydrogenase (EC 1.1.1.37) activity and the total protein content of brain cytosol remained unaltered with all doses of T₃ used. The thyroid hormone specificity of cytosolic NADP-dependent malic enzyme in fish brain is thus documented.     

Gene replacement in Dictyostelium: generation of myosin null mutants.

The eukaryotic slime mold Dictyostelium discoideum has a single conventional myosin heavy chain gene (mhcA). The elimination of the mhcA gene was achieved by homologous recombination. Two gene replacement plasmids were constructed, each carrying the G418 resistance gene as a selective marker and flanked by either 0.7 kb of 5' coding sequence and 0.9 kb of 3' coding sequence or 1.5 kb of 5' flanking sequence and 1.1 kb of 3' flanking sequence. Myosin null mutants (mhcA- cells) were obtained after transformation with either of these plasmids. The mhcA- cells are genetically stable and are capable of a variety of motile processes. Our results provide genetic proof that in Dictyostelium the conventional myosin gene is required for growth in suspension, normal cell division and sporogenesis, and illustrate how gene targeting can be used as a tool in Dictyostelium.     

Conformational analysis of PKI(5-22)amide, the active inhibitory fragment of the inhibitor protein of the cyclic AMP-dependent protein kinase.

Fourier-transform i.r. spectroscopy, 1H-n.m.r. spectroscopy and X-ray scattering were used to study the conformation and shape of the peptide PKI(5-22)amide, which contains the active site of the inhibitor protein of the cyclic AMP-dependent protein kinase [Cheng, Van Pattern, Smith & Walsh (1985) Biochem. J. 231, 655-661]. The X-ray-scattering solution studies show that the peptide has a compact structure with Rg 0.9 nm (9.0 A) and a linear maximum dimension of 2.5 nm (25A). Compatible with this, Fourier-transform i.r. and n.m.r. determinations indicate that the peptide contains approx. 26% alpha-helix located in the N-terminal one-third of the molecule. This region contains the phenylalanine residue that is one essential recognition determinant for high-affinity binding to the protein kinase catalytic site.     

Immunophenotyping of acute myeloid leukaemia: relevance of analysing different lineage-associated markers

The immunophenotype of 135 previously untreated patients with FAB defined acute myeloid leukaemia (AML) was studied at diagnosis. The panel of reagents included monoclonal antibodies (MoAb) recognising myeloid-associated determinants (CD11, CD13, CD14, CD33 and others) as well as MoAb directed towards lymphoid antigens (CD7, CD10, CD19) and TdT. The results indicate that CD13 and/or CD33 are consistently expressed in AML and only rarely in ALL blasts (131/135 + ve cases, versus 4/130 in ALL). Lymphoid antigen expression was rarely detected when CD10 and CD19 were investigated in AML (0.9% and 2% + ve cases, respectively), whereas significant positivities were found for TdT and CD7 (20% and 10% respectively). Concerning FAB subtypes, two new MoAb (LAM3 and LAM7) proved very useful in the specific recognition of AML with monocytic features. The phenotype CD13+ and/or CD33+, CD9+, HLA-DR- was found to be almost exclusive for M3 AML. The response to induction chemotherapy was analysed in CD7+ and in TdT+ patients. In the latter group a statistically significant lower response rate was found with respect to TdT-ve-AML patients.     

A peptidyl alpha-amidation activity in chromaffin granules of bovine adrenal medulla

Peptidyl alpha-amidation activity in bovine adrenal medulla has been localized in chromaffin granules by density gradient centrifugation. The activity was found to be both soluble and membrane-associated. Both enzymatic activities were stimulated by the addition of Cu2+ and ascorbate. The pH maximum for alpha-amidation in the chromaffin granules in pH 8.0-8.5. By gel filtration, the soluble enzyme activity appeared as a protein of approx. 40 kDa. It is suggested that this enzyme is involved in the carboxyl-terminal amidation of metorphamide, amidorphin and neuropeptide Y.     

Aggregation of 27 oral bacteria by human whole saliva

Twenty-seven oral strains of the genera Actinomyces (5), Bacteroides (3), and Streptococcus (19) were tested for aggregation by human whole saliva, as well as the effect of culture medium, Ca-ions, and bacteria concentration thereupon. Of the media tested, GF-broth gave rise to less interference by autoaggregation or higher aggregation titers than BHI and TSB, and was used throughout this study. In most cases, Ca-ions (1 mM) only enhanced the rate of induced aggregation, whereas raising the bacteria concentration increased the rate of both induce- and autoaggregation. The final titers, ranging from 1–64, were hardly affected by these parameters, except those of S. rattus HG 59 and S. mutans HG 199, which were respectively increased and decreased by Ca-ions. Saliva-induced aggregation was observed for 21 strains of A. viscosus, A. naeslundii, A. israelii, B. gingivalis, B. intermedius, S. cricetus, S. mutans, S. rattus, S. sanguis, and S. sobrinus, mostly within 15 min to 3 h. Seventeen of these strains also showed autoaggregation, usually well after the onset of induced aggregation. Any potential induced aggregation of B. gingivalis HG 91 was always masked by autoaggregation, as well as that of the S. mutans strains under a particular set of conditions. The aggregation rate and titer varied considerably in a mutually unrelated and strain-dependent way. These microtiterplate data were matched by the 5 spectrophotometric patterns observed for saliva-bacterial interaction, which moreover, gave the better differentiation between induced and autoaggregation. In conclusion, most strains tested can show rapid saliva-induced aggregation in a strain-dependent way, yet strongly affected by the experimental conditions and interference from autoaggregation.     

Beta 1 and beta 2 adrenergic agonists in exocrine pancreatic secretion in the rabbit

The effect of Dobutamine (a beta 1-adrenergic agonist) and Terbutaline (a beta 2-adrenergic agonist) on exocrine pancreatic secretion was studied in anaesthetized rabbits, simultaneously controlling pancreatic blood flow and blood pressure. The secretion of fluid and ions (bicarbonate, sodium and potassium) was unaffected by the infusion of Dobutamine (8 micrograms.kg-1.min-1) or Terbutaline (10 micrograms.kg-1.min-1). Neither were pancreatic blood flow or mean blood pressure altered. Dobutamine or Terbutaline depress the function of the acinar cells, amylase secretion being more affected by the action of Terbutaline. The results show that beta 1 and beta 2-adrenergic stimulation has no effect on the ductular cells but does decrease the secretion by the acinar cells.