Inhibition by heparin and dextran sulfate of stimulated rat pancreatic adenylate cyclase

Heparin inhibited the adenylate cyclase activity of semipurified rat pancreatic plasma membranes stimulated by hormones and by Gpp(NH)p but not by fluoride or when in the persistently active state. When observed, the inhibition was rapid and sustained. It was of a noncompetitive type and never exceeded 20% for secretin. The inhibition of Gpp(NH)p-stimulated activity was more pronounced (48% inhibition at a heparin concentration of 50 μg/ml). For the C-terminal octapeptide of pancreozymin (CCK-8)-stimulated adenylate cyclase, the inhibition amounted to 93% at 50 μg/ml. This inhibition was competitive at low heparin concentration and of a mixed type above 10 μg/ml. Besides, heparin inhibited (I₅₀ = 6 μg/ml) the binding of peptides of the CCK family to their specific receptors without affecting the apparent K_d value of binding. Taken together, these relatively specific effects of heparin gave evidence in favor of the existence of CCK spare receptors. Dextran sulfate was more potent than heparin as an inhibitor of adenylate cyclase activation while chondroitin-4-sulfate and chondroitin-6-sulfate were ineffective. Dansylated pancreatic plasma membranes exhibited characteristics of adenylate cyclase activation by CCK-8 which were similar to those found for untreated membranes exposed to heparin.     

Vererbung der Chloroplasten-DNA bei Munzia-Oenotheren

Die Analyse der DNA aus den Chloroplasten der Oenothera berteriana und der Oe. odorata durch Fragmentierung mit den Restriktionsendonukleasen EcoR I, BamH I, Bst I, Kpn I sowie Sma I und anschließende elektrophoretische Trennung der Bruchstücke erbrachte eindeutige molekulare Unterschiede zwischen den beiden Plastomen. Die vorhandenen Unterschiede erlauben die Identifizierung der elterlichen Chloroplasten-DNAs in einer ganzen Reihe von Hybriden, die aus reziproken Kreuzungen sowie aus daran anschließenden Rückkreuzungsfolgen hervorgegangen sind. Die so ermittelte genetische Konstitution der Piastiden der einzelnen Hybridformen stimmt mit der aus der Kreuzungsherkunft erschlossenen überein. Die Chloroplasten-DNA der jeweiligen Mutterpflanze findet sich unverändert in den Bastarden wieder, deren genetische Information im Zellkern aus Chromosomenkomplexen beider Elternformen verschieden gemischt ist. Die Unterschiede sind auch dann reproduzierbar, wenn die Piastiden der einen Art mit dem gesamten Kerngenom der anderen Art kombiniert oder noch zusätzlich vom Cytoplasma der anderen Art umgeben sind. Die DNA in den Chloroplasten hat sich also weder unter dem Einfluß artfremder Kern-Chromosomen-Komplexe noch unter dem Einfluß artfremden Cytoplasmas verändert.     

Microtubules in the epidermal cells of Carausius morosus (Br.). Their pattern and relation to pigment migration

The existence of one or several systems of microtubules, consisting of a central bundle that branches off towards the basal and distal ends of epidermal cells of Carausius morosus has been shown by indirect immuno-fluorescence microscopy using monospecific anti-tubulin. The pattern of microtubules coincides with the position of the ommochrome granules and their migration path during physiological colour change. The ommochrome granules stick to isolated bundles of microtubules. Small bundles of microtubules extend almost perpendicularly towards the apical cell membrane where they are attached. Distally they are covered by pore channels within the cuticle. Parallel to the basal cell membrane and in close contact with it, there are very small bundles of microtubules. These findings strongly support the idea that during physiological colour change the ommochrome granules migrate along a firmly fixed system of microtubules.     

The isolation and amino acid/sugar composition of human fibroblastoid interferon.

Human fibroblastoid interferon produced from an established human cell line was purified by controlled-pore glass and concanavalin A-Sepharose column chromatography followed by preparative two-dimensional gel electrophoresis. The purification procedure provided a 10% recovery of pure interferon with good reproducibility. The purified protein was homogeneous with respect to its molecular weight of 20,000 and net electrical charge at pH 2.5. Interferon of high specific activity of 5 x 10(8) units/mg of protein was directly demonstrated in the polyacrylamide gel before staining with Coomassie brilliant blue. Parallel purification of a sham-induced interferon preparation did not yield an equivalent product indicating the purified interferon is not derived from uninduced cells or from the fetal calf serum of the tissue culture growth medium. Pure interferon was radioiodinated by Bolton-Hunter reagent. Amino acid analysis of the pure preparation shows interferon to be a leucine-rich glycoprotein containing a high percentage of glutamic/glutamine residues and that disulfide bridges(s) are important for its biological activity.     

Association of binding sites for guanine nucleotides with adenylate cyclase activation in rat pancreatic plasma membranes. Interaction of gastrointestinal hormones

1. The activation of rat pancreatic adenylate cyclase by guanosine 5'-(beta-gamma-imido)triphosphate (p[NH]ppG) and GTP, and by the two gastrointestinal hormones pancreozymin (as C-terminal octapeptide) and secretin was correlated with the binding of [8-3H]guanosine 5'-(beta-gamma-imido)triphosphate to rat pancreatic plasma membranes. 2. The low basal adenylate cyclase activity was stimulated 17-fold by p[NH]ppG (after a 2 min lag period), 3,5-fold only by GTP, 21-fold by C-terminal octapeptide of pancreozymin, and 8-fold by secretin. GTP inhibited competitively the activation of adenylate cyclase by p[NH]ppG with a Ki,app almost identical with the Ka,app (0.3 micron). p[NH]ppG and GTP enhanced the stimulation by secretin more markedly than that by the C-terminal octapeptide of pancreozymin, leading to the same maximal activity. Both hormones suppressed the lag period of activation by p[NH]ppG. 3. The binding of [8-3H]p[NH]ppG was dependent on time, temperature and Mg2+ and it was also a saturable and reversible process. Scatchard plots with a concavity upward were linearized after co-addition of ATP, Mg2+ and an ATP-regenerating system that abolished low-affinity sites for p[NH]ppG without saturating higher affinity sites, GTP, ITP and UTP inhibited [8-3H]p[NH]ppG binding to the high-affinity sites in concentration ranges identical with those found for adenylate cyclase activation. Considerable binding of [8-3H]p[NH]ppG was still evident at 20 degrees C, but enzyme activation was not observed any more, except in the presence of hormones.     

Bienenbrut statt Ameisenpuppen als Futtermittel zur Handaufzucht nestjunger Singv?gel

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