Structural re-evaluation of the neurosecretory system in the crayfish eyestalk

Summary The topography of the neurosecretory system in the decapod eyestalk has not been precisely delineated with light microscopy. Cobalt iontophoresis and electron microscopy have proved useful in clarifying the microstructure of this system. The sinus gland (sg) of the crayfish eyestalk consists of aggregated axon terminals which end at or near the blood space, lontophoresing cobalt back through the cut base of the sinus glands reveals proximal cell bodies in the eyestalk only in the X organ (Xo) region. Electron microscopy demonstrates that axons from about 115 neurosecretory cell bodies in the Xo form the Xo-sg tract. Intermingled with these Xo somata are smaller non-neurosecretory cell bodies which do not send axons into the sinus gland. One of these exhibits catecholamine fluorescence. Backfilling also reveals a second group of fibres which run from the brain along the optic tract and into the sinus gland. These brain-sg fibres are smaller in diameter than Xo-sg axons and lack neurosecretory vesicles. From these fibres collaterals extend into the eyestalk neuropil, especially in the proximity of the visual elements. The possible function of these non-neurosecretory processes within the sinus gland is discussed.This work was supported by a National Research Council of Canada grant     

Potassium-induced insulin release and voltage noise measurements in single mouse islets of Langerhans

Summary Insulin release and membrane potential fluctuations in response to increased extracellular potassium [K⁺] _o have been measured in single perifused islets of Langerhans from normal mice. An increase in [K⁺] _o from 5mm to 50mm induced a transient insulin release with a peak at about 1 min. The peak value was [K⁺] _o -dependent but the half-timet _1/2 for the decline was constant at nearly 1 min. 2.5mm cobalt completely inhibited the potassium-induced stimulation of insulin release. The insulin release elicited by 28 and 50mm [K⁺] _o was similar in terms of peak, total release and half-time from maximum release. Stepwise increase in [K⁺] _o from 10 to 28 to 50mm resulted in a normal response to 28mm but no peak of release after the 28 to 50mm increase. The results indicate good correlation between excess voltage noise, thought to reflect calcium channel activity, and insulin release evoked by changing extracellular potassium.     

Cytochrome function in the cyclic electron transport pathway of chloroplasts

Flash excitation of isolated intact chloroplasts promoted absorbance transients corresponding to the electrochromic effect (P-518) and the α-bands of cytochrome b₆ and cytochrome f. Under conditions supporting coupled cyclic electron flow, the oxidation of cytochrome b₆ and the reduction of cytochrome f had relaxation half-times of 15 and 17 ms, respectively. Optimal poising of cyclic electron flow, achieved by addition of 0.1 μM 3-(3,4-dichlorophenyl)-1,1-dimethylurea, increased phosphorylation of endogenous ADP and prolonged these relaxation times. The presence of NH₄Cl, or monensin plus NaCl, decreased the half-times for cytochrome relaxation to approximately 2 ms. Uncouplers also revealed the presence of a slow rise component in the electrochromic absorption shift, with formation half-time of about 2 ms. The inhibitors of cyclic phosphorylation antimycin and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone abolished the slow rise in the electrochromic shift and prolonged the uncoupled relaxation times of cytochromes b₆ and f by factors of ten or more.These observations indicate that cytochrome b₆, plastoquinone and cytochrome f participate in a coupled electron transport process responsible for cyclic phosphorylation in intact chloroplasts. Estimations of cyclic phosphorylation rates from 40 to 120 μmol ATP/mg chlorophyll per h suggest that this process can provide a substantial fraction of the ATP needed for CO₂ fixation.     

Bacteriochlorophyll a cation radical in solution and in reaction centers of Rhodopseudomonas sphaeroides. Resonance Raman scattering

Resonance Raman spectra of the π-cation of bacterio-chlorophyll a in solution at 30 K are reported and discussed. Outer C

C bonds of the pyrroles and the methine bridges are weakened by the ionization, while C

N and Mg-N bonds remain essentially unaffected. Resonance Raman spectra of reaction centers suggest that the positive charge on P-870⁺ should be localized on a single bacteriochlorophyll molecule by the lifetime of the scattering process (≈ 10^?13 s).     

Orientation of pigments and pigment-protein complexes in the green photosynthetic bacterium Prosthecochloris aestuarii

The orientation of pigments and pigment-protein complexes of the green photosynthetic bacterium Prosthecochloris aestuarii was studied by measurement of linear dichroism spectra at 295 and 100 K. Orientation of intact cells and membrane vesicles (Complex I) was obtained by drying on a glass plate. The photochemically active pigment-protein complexes (photosystem-protein complex and reaction center pigment-protein complex) and the antenna bacteriochlorophyll a protein were oriented by pressing a polyacrylamide gel. The data indicate that the near-infrared transitions (Q_y) of bacteriochlorophyll c and most bacteriochlorophyll a molecules have a relatively parallel orientation to the membrane, whereas the Q_y transitions of the bacteriochlorophyll a in the antenna protein are oriented predominantly perpendicularly to the membrane. Carotenoids and the Q_x transitions (590–620 nm) of bacteriochlorophyll a, not belonging to the bacteriochlorophyll a protein, have a relatively perpendicular orientation to the membrane. The absorption and linear dichroism spectra indicate the existence of different pools of bacteriochlorophyll c in the chlorosomes and of carotenoid and bacteriopheophytin c in the cell membrane. The results suggest that the photosystem-protein and reaction center pigment-protein complexes are oriented with their short axes approximately perpendicular to the plane of the membrane. The symmetry axis of the bacteriochlorophyll a protein has an approximately perpendicular orientation.     

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

Structural changes in the purified $\text{(}\text{Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-ATPase}$ accompanying detergent inactivation were investigated by monitoring changes in light scattering, intrinsic protein fluorescence, and tryptophan to β-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 $\text{(}\text{Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-ATPase}$ and $\text{p-}\text{nitrophenylphosphate}$ activity by digitonin (which occurs during the rapid phase of inactivation) is unlikely 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 $\text{(}\text{Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-ATPase}$ or $\text{p-}\text{nitrophenylphosphatase}$ activity and that the rate-limiting step in the slow inactivation phase involves dissociation of an essential lipid.     

Cytokinin biosynthesis in roots of corn

Removal of the quiescent center (QC) from the root apex of maize (Zea mays L., cv. Kelvedon 33) initiates a set of events which culiminate in the regeneration of an intact apex with a newly formed QC. Concomitant with the formation of a new QC is a marked reduction in extractable cytokinins in the tissue of the proximal meristem. Replacing the excised QC with a Dowex (acidic cation-exchange resin) bead affects both root growth and QC regeneration. Root growth is inhibited by plain Dowex beads and Dowex beads treated with zeatin; this inhibition is reversed if the beads have been treated with CaCl₂ (±zeatin). Dowex beads treated with zeatin delay the formation of a new QC; this effect is the same whether or not the beads also contain CaCl₂. The results of this investigation support the notions that cytokinin biosynthesis in roots is a result of activities of both the QC and the proximal meristem, and that cytokinins, at least if supplied exogenously, can play a role in root morphogenesis by delaying the regeneration of the QC.Abbreviations used throughout the text PM proximal meristem - QC quiescent center - RC root cap     

Non-random X-chromosome expression early in mouse development

We have used a sensitive electrophoretic technique for estimating the activity, or ratio, of two allozymes of the X-chromosome-linked enzyme phosphoglycerate kinase (PGK-1), in order to investigate the randomness of X-chromosome expression in the derivatives of the three primary cell lineages of the early mouse conceptus. The maternally derived Pgk-1 allele is preferentially expressed in the derivatives of the primitive endoderm and trophectoderm lineages at 6 1/2 days post coitum in Pgk-1^a/Pgk-1^b heterozygous conceptuses, and in the one informative 5 1/2-day heterozygous conceptus analysed. This evidence for preferential expression of the maternally derived X chromosome (X^m), so soon after the time of X-chromosome inactivation, favors the possibility that the preferential expression of X^m is a consequence of primary non-random X-chromosome inactivation, rather than a secondary selection phenomenon. The majority of embryos analysed at 4 1/2 and 5 1/2 days pc produced only a single PGK-1 band, corresponding to the allozyme produced by the Pgk-1 allele on X^m, although 50% of these embryos should have been heterozygous females. Possible explanations are discussed.     

Neurological and electroencephalographic changes in newborns treated with prostaglandins E2 and E2

Six newborns with obstructive right heart lesions were examined neurologically and electroencephalographically during treatment with prostaglandin (PG) E₁ or E₂ given to maintain patency of the ductus arteriosus and to increase pulmonary blood flow. PG was administered intravenously or intraarterially in the aortic isthmus proximal to the ductus arteriosus. Besides a rise in arterial oxygen saturation, all patients had some sign of central nervous system involvement. The electroencephalogram showed minor changes suggestive of sedation. In addition, three patients in whom PG given intravenously presented various combinations of neurological abnormalities (“myoclonic jerks”, apnoeic spells, hiccup) of subcortical origin. Side-effects subsided after stopping the treatment anf posed no problem in the management of the patients. These findings confirm the usefulness and safety of the PG therapy and indicate that the intraaortic route of administration is preferable.