Association of Serotonin, Dopamine, or Noradrenaline with an Actin-Like Component in Pheochromocytoma (PC12) Cells

A rat pheochromocytoma (PC12) cell line was used to examine the possibility that 5-hydroxytryptamine (serotonin), 3,4-dihydroxyphenylethylamine (dopamine), or noradrenaline may be associated with cytoplasmic actin, as was suggested by previous in vitro binding studies on an actin-like protein from rat brain synaptosomes. When PC12 cells were incubated with [3H]serotonin. [3H]dopamine, or [3H]noradrenaline for 30 min at 37 degrees C, approximately 2-4% of the radioactivity present in the cells was found to be associated with a high-molecular-weight (actin-like) component in supernatant fractions. Evidence relating this monoamine binding component to actin filaments includes: (a) its strong absorption by myosin filaments at low ionic strength: (b) a decrease in its affinity for myosin in the presence of 1 mM ATP, which lowers the affinity of authentic actin for myosin: (c) displacement of bound [3H]serotonin from it by DNase I, which binds strongly to actin and which inhibits [3H]serotonin binding to actin in vitro; (d) an increase in its binding of each monoamine (by 25-40%) after PC12 cells were preincubated with 10 microM cytochalasin B (a drug that induces depolymerization of F-actin). These findings suggest that serotonin, dopamine, or noradrenaline may associate with actin filaments in vivo.     

Properties and Partial Purification of Choline Acetyltransferase from the Nematode Caenorhabditis elegans

We have stabilized and studied choline acetyltransferase from the nematode Caenorhabditis elegans. The enzyme is soluble, and two discrete forms were resolved by gel filtration. The larger of these two forms (MW approximately 154,000) was somewhat unstable and in the presence of 0.5 M NaI was converted to a form indistinguishable from the "native" small form (MW approximately 71,000). We have purified the small form of the enzyme greater than 3,300-fold by a combination of gel filtration, ion-exchange chromatography, and nucleotide affinity chromatography. The purified preparation has a measured specific activity of 3.74 mumol/min/mg protein, and is free of acetylcholinesterase and acetyl-CoA hydrolase activities. The Vmax of the purified enzyme is stimulated by NaCl, with half-maximal stimulation at 80 mM NaCl. The Km for each substrate is also affected by salt, but in different manners from each other and the Vmax; the kinetic parameter Vmax/Km thus changes significantly as a function of the salt concentration.     

Evidence for the participation of disulfide and sulfhydril groups in the specific binding of [3H]prazosin in cerebral cortex

The tritiated ₁ antagonist prazosin [³H]PRZ binds specifically and with high affinity to postsynaptic adrenoceptors in membrane preparations from cerebral cortex. Since adrenoceptors are of protein nature, it was of interest of investigate the possible role of disulfide (—SS—) and sulfhydril (—SH) groups in the binding of [³H]PRZ. Pretreatment of the membranes with the disulfide and sulfhydryl reactivesdl0Dithiothreitol,l-Dithiothreitol, Dithioerythritol or 5,5-Dithiobis-(2-nitrobenzoic acid) (DTNB), alone or in combination with the alkylating agent N-Methylmaleimide (NMM), decreased specific [³HPRZ binding, with minor changes in the non-specific counts. Saturation experiments revealed that all these reagents reduced the affinity of the binding site for [³H]PRZ, as judged by theK _d 25°C, but only the alkylating agent NMM and the oxydizing reagent DTNB produced in addition to the increase inK _d, a decrease of the maximum binding capacity (B _max). The present results provide evidence for a participation of—SS—and/or—SH groups in the recognition site of the ₁-adrenoceptor of cerebral cortex.     

Variations in the sizes of gonads,eggs and larvae of the dace,Leuciscus leuciscus

Synopsis Prespawning female dace were examined in 7 successive years; in 6 years mean egg size (mm³) and egg number were inversely related and hence the ovary weights of equivalent-sized females were constant. Fecundity increased logarithmically with fish length, and an index of reproductive effort (ovary weight ÷ length cubed) also increased. The number of eggs per gram of ovarian tissue decreased with fish length; this was because mean egg size (mm³) increased and not because of a change in the proportion of connective tissue in the ovary. But in 1977, both egg number and mean egg size were low, although very high somatic growth had occurred in the previous, very warm, summer of 1976. Eggs from different-sized female dace were artificially fertilized, and incubated at a constant temperature. Dry weights of larvae, egg dry weights, mean egg size and larval starvation times showed linear correlations with each other and with parental (female) lengths. The progeny from the very smallest parent died several days earlier than those from the other parents. Size-related predation rates may be of more consequence than starvation death in natural populations. The optimum position of dace along the continuum between many small eggs and fewer larger eggs may vary at different levels of reproductive effort.     

The morphology and anatomy ofHydrastis (Ranunculales): Systematic reevaluation of the genus

Evidence from morphology and anatomy (including embryology), as well as from palynology, chemistry and cytology, indicates thatHydrastis is quite divergent from Ranunculaceae (in which the genus has been most often included) as well as from both Glaucidiaceae and Berberidaceae. Distinctive features ofHydrastis, which demarcate it from Ranunculaceae but which are sometimes shared by Berberidaceae, are: the unique mode of origin of the vascular supply to stamens and carpels; the micropyle being formed by both integuments; the xylem not V-shaped in cross section; scalariform vessel perforations present; haploid chromosome number 13; pollen tectum consisting of a compound layer of striae; leaf mesophyll not differentiated; the unique course of stem medullary bundles; D-galactose present. Its distinctive higher haploid chromosome number, as well as its many less-specialized character states (in floral structure, leaf anatomy, and xylem and vessel morphology), suggest thatHydrastis is a relictual primitive group which diverged early from a common ancestral stock of Ranunculaceae, Berberidaceae and probably of Circaeasteraceae; at least some of the features shared byHydrastis and one or another of the families concerned seem to be a heritage from their common ancestor. We propose a reestablishment of a monotypic family, Hydrastidaceae.     

Evidence for adenylylation/deadenylylation control of the glutamine synthetases of Rhodospirillum tenue and Rhodocyclus purpureus

The phylogenetically related phototrophic bacteria Rhodospirillum tenue and Rhodocyclus purpureus modulate activity of their glutamine synthetases by adenylylation/deadenylylation. Evidence for covalent modification includes the inhibitory effect of Mg²⁺ on the activity of glutamine synthetase extracted from cells of either species grown on excess ammonia, and the lack of Mg²⁺ inhibition of activity of the enzyme isolated from N₂-(R. tenue) or glutamine (R. purpureus)-grown cells. In addition, snake venom phosphodiesterase treatment of glutamine synthetase from either species grown on excess ammonia relieved Mg²⁺ inhibition of the enzyme (as measured via the -glutamyl transferase assay), and changed the cation specificity from Mn²⁺ to Mg²⁺ (in the biosynthetic assay).     

Eye movements and the enhancement of edges

A mathematical examination of retinal photochemistry leads to a hypothesis for Mach band phenomena based on eye movements. This retinal model suggests why minimally distinct borders fade under eye fixation and agrees qualitatively with subjective measures of border contrast as a function of overall field luminance.Deceased