Structural changes in (Na+ + K+)-ATPase accompanying detergent inactivation

Structural changes in the purified (Na+ + K+)-ATPase accompanying detergent inactivation were investigated by monitoring changes in light scattering, intrinsic protein fluorescence, and tryptophan to beta-parinaric acid fluorescence resonance energy transfer. Two phases of inactivation were observed using the non-ionic detergents, digitonin, Lubrol WX and Triton X-100. The rapid phase involves detergent monomer insertion but little change in protein structure or little displacement of closely associated lipids as judged by intrinsic protein fluorescence and fluorescence resonance energy transfer. Lubrol WX and Triton X-100 also caused membrane fragmentation during the rapid phase. The slower phase of inactivation results in a completely inactive enzyme in a particle of 400 000 daltons with 20 mol/mol of associated phospholipid. Fluorescence changes during the course of the slow phase indicate some dissociation of protein-associated lipids and an accompanying protein conformational change. It is concluded that non-parallel inhibition of (Na+ + K+)-ATPase and p-nitrophenylphosphate activity by digitonin (which occurs during the rapid phase of inactivation) is unlikey to require a change in the oligomeric state of the enzyme. It is also concluded that at least 20 mol/mol of tightly associated lipid are necessary for either (Na+ + K+)-ATPase or p-nitrophenylphosphatase activity and that the rate-limiting step in the slow inactivation phase involves dissociation of an essential lipid.     

The amphipathic membrane proteins associated with gangliosides: The Paul-Bunnell antigen is one of the gangliophilic proteins

Two amphipathic protein fractions soluble in organic solvents as well as in water have been isolated from the ganglioside fraction of bovine erythrocyte membranes by successive chromatography in chloroform-methanol mixture on DEAE-Sephadex, silicic acid, and α-hydroxypropylated Sephadex G50 (LH60) columns. These two fractions contained a similar low molecular weight protein but with distinctively different amino acid composition. One of these proteins has been characterized by having a strong Paul-Bunnell antigen activity and had a binding affinity to ganglioside. A similar protein without Paul-Bunnell antigen activity was isolated as the major ganglioside-associated protein.     

Temperature Interactions with Growth Regulators and Endogenous Gibberellin-like Activity during Seedstalk Elongation in Carrots

Stecklings (roots) of three cultivars of carrots (Daucus carota L.) were vernalized 10 weeks at 5 C and subsequently grown at each of three greenhouse night/day temperature regimes: high (27/32 C), medium (21/27 C), and low (15/21 C). Floral differentiation occurred first in the easy bolting cv. Scarlet Nantes, intermediate in cv. Danvers 126, and last in cv. Royal Chantenay. Stem elongation arising from the subapical meristematic region always preceded floral differentiation. Extractable gibberellin-like activity in carrot stem apices increased from harvest during the 10-week vernalization period, then remained constant even though floral differentiation and stem elongation occurred during an additional 20-week cold storage period. Low temperature had both an inductive and a direct effect on reproductive development depending on length of low temperature exposure.     

MITOSIS IN THE AQUATIC FUNGUS RHIZOPHYDIUM SPHEROTHECA (CHYTRIDIALES)

The structure of centric, intranuclear mitosis and of organelles associated with nuclei are described in developing zoosporangia of the chytrid Rhizophydium spherotheca. Frequently dictyosomes partially encompass the sides of diplosomes (paired centrioles). A single, incomplete layer of endoplasmic reticulum with tubular connections to the nuclear envelope is found around dividing nuclei. The nuclear envelope remains intact during mitosis except for polar fenestrae which appear during spindle incursion. During prophase, when diplosomes first define the nuclear poles, secondary centrioles occur adjacent and at right angles to the sides of primary centrioles. By late metaphase the centrioles in a diplosome are positioned at a 40° angle to each other and are joined by an electron-dense band; by telophase the centrioles lie almost parallel to each other. Astral microtubules radiate into the cytoplasm from centrioles during interphase, but by metaphase few cytoplasmic microtubules are found. Cytoplasmic microtubules increase during late anaphase and telophase as spindle microtubules gradually disappear. The mitotic spindle, which contains chromosomal and interzonal microtubules, converges at the base of the primary centriole. Throughout mitosis the semipersistent nucleolus is adjacent to the nuclear envelope and remains in the interzonal region of the nucleus as chromosomes separate and the nucleus elongates. During telophase the nuclear envelope constricts around the chromosomal mass, and the daughter nuclei separate from each end of the interzonal region of the nucleus. The envelope of the interzonal region is relatively intact and encircles the nucleolus, but later the membranes of the interzonal region scatter and the nucleolus disperses. The structure of the mitotic apparatus is similar to that of the chytrid Phlyctochytrium irregulare.     

Rapid isolation of plasma membranes in high yield from cultured fibroblasts.

1. A method was developed which allows the rapid preparation of pure plasma membranes in high yield from cultured fibroblasts. 2. Cells are lysed in hypo-osmotic borate/EDTA and, after differential centrifugation, the membranes collected by centrifugation on a sucrose barrier. 3. Electron microscopy of the isolated material shows large membrane vesicles essentially free from contaminating organelles. 4. There is no detectable activity of the endoplasmic-reticulum enzyme marker, NADH2--lipoamide oxidoreductase (EC 1.6.4.3), and that of succinate dehydrogenase (EC 1.3.99.1), a marker for mitochondria, is substantially decreased. Chemical compositions are in good agreement with previous observations. 5. This study confirms the usefulness of applied isotopic markers for isolating plasma membranes.     

Biliary excretion of some anionic derivatives of diethylstilboestrol and phenolphthalein in the guinea pig.

The metabolic fates and modes of excretion of diethylstilboestrol mono[35S]sulphate and diethylstilboestrol di[35S]sulphate were studied in the guinea pig. Comparative studies were also made with [G-3H]diethylstilboestrol and phenolphthalein di[35S]sulphate. Diethylstiboesterol di[35S]sulphate was extensively eliminated in the bile unchanged. After administration of diethylstilboestrol mono[35S]sulphate, extensive biliary elimination of radioactivity was also recorded. Radioactive components were identified as diethylstilboestrol disulphate, diethylstilboestrol monosulphate monoglucuronide and unchanged diethylstilboestrol monosulphate. When [G-3H]diethylstilboestrol was administered, 3H-labelled diethylstilboestrol monoglucuronide, diethylstilboestrol monosulphate monoglucuronide and diethylstilboestrol disulphate appeared in the bile. Phenolphthalein di[35S]sulphate was excreted unchanged in bile. These findings are discussed in relation to studies carried out in the rat [Barford, Olavesen, Curtis & Powell (1977) Biochem. J. 164, 423--430] and species differences are related to differences in enzyme activities in rat and guinea-pig liver.     

Habitat choice in natural populations of Drosophila

Summary Mark-release-recapture experiments performed with natural populations of Drosophila at Mather, California show that flies tend to return to their area of original capture or an area ecologically similar to it. Such habitat choice explains the microgeographic genetic differentiation we observed in the population. This behavioral difference between the flies may have a genetic component or may be environmentally induced. Either way, the results help explain how high levels of genetic variation are maintained by natural selection in these species.     

A secoisolariciresinol branched fatty diester from Salvia plebeia seed

The structure of a second new lignan diester from Salvia plebeia seed has been determined. Hydrolysis of this diester yields two compounds, 12-methyltetradecanoic acid and secoisolariciresinol.     

Factors affecting the termination of cardiovascular actions of 10, 10-difluoro, 13-dehydroprostacyclin

Experiments were conducted to determine why 10,10-difluoro, 13-dehydroprostacyclin (DF₂-PGI₂) has a long vascular relexant activity but like PGI₂ hads a short duration of effect . DF₂-PGI₂ produced depressor responses in anesthetized dogs which were not affected by nephrectomy suggesting that the kidney was not responsible for the termination of action. DF₂-PGI₂ given intravenously or into the ascending oarta produced depressor responses of a similar magnitude but injection of the same doses into the hepatic portal circulation resulted in a large attenuation of responses. The data suggest hepatitic, but not pulmonary, metabolism of DF₂-PGI₂. Injection or infusion of PGI₂ and DF₂-PGI₂ into the hindlimb circulation caused vasodilation of a similar duration suggesting diffusion from tissue sites as another mechanims of termination of action.     

Specific reduction of development of the Mauthner neuron lateral dendrite after otic capsule ablation in Brachydanio rerio

During development, afferent fibers may stimulate development of postsynaptic target neurons. By surgically ablating an otic vesicle in zebrafish embryos 30 hr after fertilization we deprived the developing Mauthner (M) neuron of vestibular axonal input to its lateral dendrite. After 8 days, 14 M cells were examined by light microscopy, and in each case the size and branching of the lateral dendrite was reduced. No consistent changes were observed in shape and size of other regions of the deprived cells or in the contralateral control cells. Synapses onto five of these pairs of cells were examined by electron microscopy. Except for missing vestibular terminals on the deprived dendrites, the synaptic input to the dendrites and to other regions of the M cell was normal in distribution and pattern. These data suggest that growth-promoting or trophic effects of vestibular axons upon the M cell are localized to its lateral dendrite.