Viability and dissemination of spermatia of Gracilaria verrucosa (Gracilariales,Rhodophyta)

The dissemination and viability of Gracilaria verrucosa spermatia were tested. Crosses were performed among three males and three females from Cape Gris Nez, northern France. Laboratory experiments show that spermatia have a mean fertile life of about five hours. Field studies show that spermatia are dispersed by stream and tidal currents and that fertilization can occur at least 80 m from a population.     

Serum activity of the key gluconeogenic enzymes in carbon-tetrachloride-induced experimental hepatotoxicity

Serum activity has been measured in three of the key enzymes in the gluconeogenic pathway in rats subjected to experimental hepatotoxicity after intraperitoneal administration of carbon tetrachloride. The levels of phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1,6-biphosphatase (FBPase) showed a similar behavior to the transaminase (AST and ALT), increasing markedly with respect to the controls at 12 h after administration of the poison, reaching their maximum peak of activity at between 24 and 36 h, and returning to normal values at 96 h. The activity of glucose-6-phosphatase was not significantly modified throughout the treatment. These results seem to demonstrate that the determination of the serum activity of PEPCK and FBPase could be a sensitive and specific marker of hepatic cytolysis.     

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.     

Asialoglycoprotein receptors in hepatic regeneration

The hepatic binding protein which is responsible for receptor-mediated endocytosis of desialylated glycoproteins undergoes cell-cycle dependent modulation of its expression. Endocytosis of desialylated orosomucoid by hepatocytes isolated from regenerating liver following two-thirds hepatectomy is reduced by 80% and returns to normal when regeneration is substantially complete. This decrease in endocytotic activity is due to selective loss of cell-surface associated receptor during liver regeneration.     

Axonal Transport, Deposition, and Metabolic Turnover of Glycoproteins in the Rat Optic Pathway

Abstract: Following intraocular injection of [³H]fucose in the rat, radioactive glycoproteins are rapidly transported to the nerve terminals in at least two waves, one with a peak at 8 h and a second with a peak at about a week. The molecular weight distribution of radioactive peptides in ach transport wave as determined by gel electrophoresis in buffers containing sodium dodecyl sulfate is very similar. Most of the many glycopeptides in the first wave of rapid transport pass through the optic tract in unison (apparent half-life of about 15 h) and are preferentially destined for the nerve endings. However, two proteins of apparent M. W. 28,000 and 49,000 are preferentially retained in the axons. The remaining proteins, after reaching the nerve endings (superior colliculus), decay with apparent half-lives ranging from 17 to 34 h. During the second wave a large amount of the 28,000 and 49,000 M. W. peptides are again preferentially retained in the axons. The remaining proteins, on reaching the nerve endings, decay with apparent half-lives ranging from 5 to 9 days. Subcellular fractionation of the superior colliculus supports the hypothesis that the 49,000 and 28,000 M. W. peptides are the predominantly labeled glycoproteins present in myelinated axons (representing over 50% of the radioactive glycoproteins 7 days following injection), although they are probably also present in membranes of the nerve endings. A comparison with glycoprotein transport in other tracts (geniculocortical and nigrostriatal tracts) suggests that glycoprotein transport in these pathways has many similarities to glycoprotein transport in the retinal ganglion cells, and that the optic system is a good general model for axonal transport in the CNS.     

Axonal Transport and Metabolism of Glycoproteins in Rat Sciatic Nerve

The distribution of 5'-nucleotidase activity, dopaminergic [3H]spiperone binding sites, and [3H]quinuclidinyl benzilate (QNB) binding sites in different subcellular fractions of bovine caudate nucleus has been studied. Each activity was enriched in a microsomal (P3) preparation from that tissue. The microsomal preparation was further fractionated by different techniques. First, the P3 fraction, or a sonicated P3 fraction, was fractionated on a discontinuous sucrose density gradient. Second, the P3 fraction, or a digitonin pretreated P3 fraction, was fractionated on a continuous sucrose density gradient. The results obtained demonstrate that 5'-nucleotidase activity does not cofractionate with radioligand binding activity, although no difference between the distributions of [3H]spiperone binding and [3H]QNB binding were seen. It is concluded that the two radioligand binding activities are located on nonglial membranes.     

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.