Biological activity of gibberellin analogues

In order to determine the significance of the C-6 carboxyl group for the biological activity gibberellin A₃, 6-epigibberellin A₃, 7-norgibberellin A₃, 6-methyl-7-norgibberellin A₃, and 7-homogibberellin A₃ were studied using dwarf pea, dwarf maize, dwarf rice, dwarf barley and -amylase bioassays. All gibberellin A₃(GA₃)derivatives tested were considerably less active than GA₃. In all biossays, 6-epi-GA₃ showed a low activity of the same order, whereas 6-methyl-7-nor-GA₃ was inactive. Surprisingly, 7-nor-GA₃ had some activity in the dwarf rice (root application), dwarf barley, and -amylase bioassay, in contrary to its low potency in the dwarf pea, dwarf maize, and dwarf rice (micro drop) bioassay. 7-Homo-GA₃ was primarily active in the dwarf maize, dwarf barley and dwarf rice bioassay. It also caused antigibberellin effects in dwarf rice. The results demonstrate that the C-6 carboxyl group is not absolutely essential for biological activity of gibberellins. The different activities of 7-nor-GA₃ observed in the various test systems may indicate that the C-6 carboxyl group is a structural requirement more for uptake and/or transport processes than for receptor affinity.Abbreviation GA₃ gibberellic acid     

Analysis of cellular interactions in density-dependent inhibition of 3T3 Cell proliferation

Subpopulations of different proliferative status are determined during cell-density dependent proliferation of 3T3 cells. From these data the probability of conversion of proliferative to quiescent cells is derived and found to correlate well with published data on binding of growth-inhibiting factors secreted from growth-inhibited cells.Based on material presented at the Symposium Intercellular Communication Stuttgart, September 16–17, 1982     

Formation of human immunoreactive LMW and HMW-kininogens during coagulation. Comparison with bradykinin activity

Variations of the levels of human HMW and LMW kininogens have been studied in serum and in plasma incubated in vitro during 30 hours, at three different temperatures: 4 degrees, 22 degrees and 37 degrees C. There is a small difference between the level of LMW kininogen in plasma and in serum, but the serum and plasma level of LMW kininogen are almost stable during the time of incubation at the three temperatures. However, HMW kininogen is reduced in serum to about fifty percent of its plasma level. It decreases in plasma and in serum during incubation, overall at 4 degrees C. A strict parallelism stays between the radioimmunoassay and the bioassay.     

Stimulation of bone resorption in organ culture by cholera toxin

Bone resorption in organ cultures of neonatal mouse calvaria was stimulated by choleragen (cholera enterotoxin) in a dose-related manner (0.5 to 5.0 ng/ml). Stimulation was potentiated by the cyclic nucleotide phosphodiesterase inhibitor isobutylmethylxanthine (4 μM) and was inhibited by human calcitonin (100 ng/ml), but not by indomethacin (0.7 μM), an inhibitor of the fatty acid cyclooxygenase. The action of choleragen on cyclic AMP accumulation and bone resorption was consistent with the known characteristics of this toxin: 1. choleragen increased cyclic AMP accumulation in bone cultures; 2. there was a lag period (20 – 120 min) prior to an increase in cyclic AMP accumulation following addition of choleragen; 3. incubation with choleragen for only 4 h stimulated bone resorption in the subsequent 44 h as much as did continuous incubation with choleragen for 48 h; and 4. choleragenoid, the biologically inactive toxoid, did not stimulate bone resorption in the concentration range in which choleragen was active. We conclude that activation of adenylyl cyclase and the subsequent increase in cyclic AMP production can stimulate bone resorption, and that cyclic AMP may, therefore, be involved in the enhanced bone resorption mediated by parathyroid hormone and other agents which increase cyclic AMP in bone.     

Relationship between the chromatoid body and the acrosomal system in early spermatids of Myxine glutinosa L.

Summary A transient close relationship between the chromatoid body and the developing acrosome is demonstrated in early spermatids of Myxine glutinosa.This work was supported by the Norwegian Research Council for Science and Humanities (NAVF, Grant Nr. D 61.44) and the Austrian Fonds zur Förderung der wissenschaftlichen Forschung, Projekt 2183     

Cell surface charge and regulation of cell division of 3T3 cells and transformed derivatives.

The cell surface charge of 3T3, 3T6, SV40-3T3 cells and trypsin-, neuraminidase- and serumtreated preparations of these has been characterized by microcell electrophoresis. At 25 °C, density-inhibited 3T3 cells show a decrease in electrophoretic mobility when treated with various stimuli of cell division. This effect is not observed at 25 °C for transformed derivatives. The surface charge configuration of various cell preparations exhibits a thermal transition which is located within a temperature range characteristic of each preparation. These and other results from cell electrophoresis, taken together with those obtained in agglutination studies by other authors, are considered evidence for the occurrence in the plasma membrane of these cells of a twodimensional phase separation. The temperature range of this phase separation is shifted on treating the cells by growth stimuli. This effect might be an indication of a basic trigger mechanism in the cell cycle.     

Sensitivity of the S1 neuronal calcium network to insulin and Bay‐K 8644 in vivo: Relationship to gait,motivation, and aging processes

Neuronal hippocampal Ca²⁺ dysregulation is a critical component of cognitive decline in brain aging and Alzheimer''s disease and is suggested to impact communication and excitability through the activation of a larger after hyperpolarization. However, few studies have tested for the presence of Ca²⁺ dysregulation in vivo, how it manifests, and whether it impacts network function across hundreds of neurons. Here, we tested for neuronal Ca²⁺ network dysregulation in vivo in the primary somatosensory cortex (S1) of anesthetized young and aged male Fisher 344 rats using single‐cell resolution techniques. Because S1 is involved in sensory discrimination and proprioception, we tested for alterations in ambulatory performance in the aged animal and investigated two potential pathways underlying these central aging‐ and Ca²⁺‐dependent changes. Compared to young, aged animals displayed increased overall activity and connectivity of the network as well as decreased ambulatory speed. In aged animals, intranasal insulin (INI) increased network synchronicity and ambulatory speed. Importantly, in young animals, delivery of the L‐type voltage‐gated Ca²⁺ channel modifier Bay‐K 8644 altered network properties, replicating some of the changes seen in the older animal. These results suggest that hippocampal Ca²⁺ dysregulation may be generalizable to other areas, such as S1, and might engage modalities that are associated with locomotor stability and motivation to ambulate. Further, given the safety profile of INI in the clinic and the evidence presented here showing that this central dysregulation is sensitive to insulin, we suggest that these processes can be targeted to potentially increase motivation and coordination while also reducing fall frequency with age.     

Reversible bacteriophage resistance by shedding the bacterial cell wall

Phages are highly abundant in the environment and pose a major threat for bacteria. Therefore, bacteria have evolved sophisticated defence systems to withstand phage attacks. Here, we describe a previously unknown mechanism by which mono- and diderm bacteria survive infection with diverse lytic phages. Phage exposure leads to a rapid and near-complete conversion of walled cells to a cell-wall-deficient state, which remains viable in osmoprotective conditions and can revert to the walled state. While shedding the cell wall dramatically reduces the number of progeny phages produced by the host, it does not always preclude phage infection. Altogether, these results show that the formation of cell-wall-deficient cells prevents complete eradication of the bacterial population and suggest that cell wall deficiency may potentially limit the efficacy of phage therapy, especially in highly osmotic environments or when used together with antibiotics that target the cell wall.     

The Crystal Structure and Small-Angle X-Ray Analysis of CsdL/TcdA Reveal a New tRNA Binding Motif in the MoeB/E1 Superfamily

Cyclic N⁶-threonylcarbamoyladenosine (‘cyclic t⁶A’, ct⁶A) is a non-thiolated hypermodification found in transfer RNAs (tRNAs) in bacteria, protists, fungi and plants. In bacteria and yeast cells ct⁶A has been shown to enhance translation fidelity and efficiency of ANN codons by improving the faithful discrimination of aminoacylated tRNAs by the ribosome. To further the understanding of ct⁶A biology we have determined the high-resolution crystal structures of CsdL/TcdA in complex with AMP and ATP, an E1-like activating enzyme from Escherichia coli, which catalyzes the ATP-dependent dehydration of t⁶A to form ct⁶A. CsdL/TcdA is a dimer whose structural integrity and dimer interface depend critically on strongly bound K⁺ and Na⁺ cations. By using biochemical assays and small-angle X-ray scattering we show that CsdL/TcdA can associate with tRNA with a 1:1 stoichiometry and with the proper position and orientation for the cyclization of t⁶A. Furthermore, we show by nuclear magnetic resonance that CsdL/TcdA engages in transient interactions with CsdA and CsdE, which, in the latter case, involve catalytically important residues. These short-lived interactions may underpin the precise channeling of sulfur atoms from cysteine to CsdL/TcdA as previously characterized. In summary, the combination of structural, biophysical and biochemical methods applied to CsdL/TcdA has afforded a more thorough understanding of how the structure of this E1-like enzyme has been fine tuned to accomplish ct⁶A synthesis on tRNAs while providing support for the notion that CsdA and CsdE are able to functionally interact with CsdL/TcdA.