Effect of desglycine-arginine vasopressin on the excitability of the command neurons of the defensive reflex in the edible snail

Perfusion of the snail (Helix lucorum L.) CNS with DG-AVP (concentration 10(-6) M) in the course of low frequency intracellular stimulation (2-4-minute interval) of the defensive reflex command neurons led to an increase in the excitability. It was expressed both in the reduction of the spike generation latency, in the increased number of spikes in response to fixed stimuli, and in the activation of pacemaker potentials. If DG-AVP was added to the medium during endoneuronal habituation, there was no increase in the excitability. It is supposed that modification of the neuronal excitability may be caused by the DG-AVP effect on the pacemaker mechanism.     

Drought resistance in pearl millet

The influence of wilting on the levels of free proline, soluble proteins, reducing sugars, starch and on the activities of nitrate reductase, invertase, amylase and pyrophosphatases have been studied in the leaf tissue of five cultivars of pearl millet at their vegetative stage under pot culture conditions. The metabolic changes could not be correlated with the yield behaviour of the cultivars under a drought condition in the field.     

Dynamics of lipid-protein interactions. Interaction of apolipoprotein A-II from human plasma high density lipoproteins with dimyristoylphosphatidylcholine

ApoA-II and dimyristoylphosphatidylcholine (DMPC) spontaneously associate to give three different complexes whose structures are determined by the initial reactant concentration and by the reaction temperature with respect to Tc (23.9 degrees C), the gel to liquid crystalline transition temperature of DMPC. At an initial lipid to protein ratio of 45/1, a single complex (2.29 x 10(5) daltons) is quantitatively formed at all temperatures between Tc - 4 degrees C and Tc + 6 degrees C. When the 45/1 complex is mixed with DMPC liposomes there is lipid exchange but no net transfer of lipid, so that the structure of the complex remains unaltered. At an initial molar ratio of 100 to 300:1, the reaction scheme is more complex. At 24 degrees C a 240/1 complex (1.5 x 10(6) daltons) is formed from a precursor 75/1 complex (3.43 x 10(5) daltons) if excess (approximately 300 mol/mol) lipid is present. The 75/1 complex exhibits lipid exchange in the presence of added DMPC liposomes at 24 degrees C, and both the 75/1 and the 240/1 complex can be converted to smaller protein-rich complexes in the presence of added apoA-II. These results suggest that the initial lipid/protein ratio and the physical state of a lipid or lipid . protein complex determines the composition and structure of the resulting complex and support the view that lipid-protein interactions are stronger than protein-protein or lipid-lipid interactions.     

Tubulin subunit carboxyl termini determine polymerization efficiency

Cleavage of tubulin by subtilisin removes a small (Mr less than 2000) fragment from the C-terminal end of both alpha and beta subunits. The resulting protein is much reduced in negative charge. The cleaved, less acidic protein retains its competence to polymerize in a GTP-dependent and cold-, GDP-, and podophyllotoxin-sensitive manner and assembles into sheets or bundles of twisted filaments. The critical concentration for polymerization of the cleaved protein is about 50-fold lower than that for intact tubulin. It is proposed that the C termini of the subunits normally impede polymerization.     

Progesterone metabolism in T47Dco human breast cancer cells--II. Intracellular metabolic path of progesterone and synthetic progestins

We show here that progesterone added to the medium of proliferating T47Dco human breast cancer cells is metabolized with a half life of 2-4h. The final metabolic product, 5 alpha-pregnan-3 beta,6 alpha-diol-20-one, (P-metabolite) is released into the medium. This structure suggested that the intracellular metabolism of progesterone involves the enzymes 5 alpha-reductase, 3 beta-hydroxysteroid dehydrogenase, and 6 alpha-hydroxylase. To investigate this pathway, the cells were incubated with a variety of potential substrates. In addition to progesterone, only precursors with the 5 alpha-configuration served as substrates for the enzymes leading to P-metabolite formation. Some precursors with a 5 beta-configuration were also metabolized by T47Dco cells. This metabolism reflected activity by either 3 beta-hydroxysteroid dehydrogenase and/or 6 alpha-hydroxylase but, in contrast to progesterone metabolism, the rates were different and the products were often mixtures. In T47Dco and MCF-7 human breast tumor cells, the reduction at C-3 followed by 6 alpha-hydroxylation, appear to be the major, and possibly only, route of progesterone metabolism. In contrast, preliminary data suggest that in normal human breast epithelial cells, this is not an exclusive route. Androgens are partially subject to the same metabolic enzymes, but synthetic progestins are not metabolized by T47Dco during an 18 h incubation.     

Nitroimidazole conjugates of bis(thiosemicarbazonato)Cu(II) - Potential combination agents for the PET imaging of hypoxia

Combination agents comprising two different pharmacophores with the same biological target have the potential to show additive or synergistic activity. Bis(thiosemicarbazonato)copper(II) complexes (e.g. ⁶⁴Cu-ATSM) and nitroimidazoles (e.g. ¹⁸F-MISO) are classes of tracer used for the delineation of tumor hypoxia by positron emission tomography (PET). Three nitroimidazole-bis(thiosemicarbazonato)copper(II) conjugates were produced in order to investigate their potential as combination hypoxia imaging agents. Two were derived from the known bifunctional bis(thiosemicarbazone) H₂ATSM/A and the third from the new precursor diacetyl-2-(4-N-methyl-3-thiosemicarbazone)-3-(4-N-ethylamino-3-thiosemicarbazone) - H₂ATSM/en. Oxygen-dependent uptake studies were performed using the ⁶⁴Cu radiolabelled complexes in EMT6 carcinoma cells. All the complexes displayed appreciable hypoxia selectivity, with the nitroimidazole conjugates displaying greater selectivity than a simple propyl derivative used as a control. Participation of the nitroimidazole group in the trapping mechanism is indicated by the increased hypoxic uptake of the 2- vs. the 4-substituted ⁶⁴Cu-ATSM/A derivatives. The 2-nitroimidazole derivative of ⁶⁴Cu-ATSM/en demonstrated superior hypoxia selectivity to ⁶⁴Cu-ATSM over the range of oxygen concentrations tested. Biodistribution of the radiolabelled 2-nitroimidazole conjugates was carried out in EMT6 tumor-bearing mice. The complexes showed significantly different uptake trends in comparison to each other and previously studied Cu-ATSM derivatives. Uptake of the Cu-ATSM/en conjugate in non-target organs was considerably lower than for derivatives based on Cu-ATSM/A.     

Alteration of domain architecture of chicken erythrocyte chromatin

The higher-order organisation of chromatin in chicken erythrocyte nuclei as a function of the ionic strength of the nuclear suspension buffer and also of the time of incubation in this buffer prior to nuclease digestion has been investigated. This organisation is described in terms of a physical parameter called the domain length. The 45-kbp-long domains of control nuclei were unravelled to give rise to domains of length 150 kbp on overnight equilibration at 0 degree C of the nuclei in standard isolation buffer containing 0.135 M NaCl prior to nuclease digestion. However, transition to the equilibrium state was preceded by a metastable and irregular domain architecture when the nuclei were incubated for only 1 h. In contrast, the domain length remained unchanged when nuclei were incubated in the isolation buffer alone for identical periods of time. The proteins dissociated at the higher ionic strength were characterised and their role in stabilising the domain structure is discussed.     

Propagation of Zea mays L. by Shoot Tip Culture: A Feasibility Study

A procedure for the stimulation of axillary bud developmentfrom young shoots of maize, their subculture to root-inducingmedia and transfer as rooted plants to soil is described. Axillarybud development was enhanced by the addition of kinetin andauxin to the culture medium. Root initiation on explanted axillarybuds, while successful with some cultivars, was variable. Anumber of mature plants with normal tassels and ears were producedfrom the lowermost buds of an original stem explant. Buds fromhigher positions on the explant exhibited different potentialitieswith some, those normally from cob producing nodes, producingshort-stalked plants with terminal female influorescences. Agradient of bud potentiality along the stem appears to be establishedextremely early after each is initiated. Zea mays., corn, maize, shoot tip culture, clone, vegetative propagation