Steroidal Saponins are not Main Building Units of the Prolamellar Body in Etioplasts

Sugar-containing lipids were analyzed by thin layer chromatographyin various cell fractions of etiolated Aoena leaves, Auena intactetioplasts and prolamellar bodies isolated from Cucurbita etioplasts.We confirmed the presence of steroidal saponins, avenacosidesA and B in etiolated leaves and crude etioplast fraction ofAvena, but scarcely detected them in Avena intact etioplastspurified by Percoll density gradient centrifugation. Saponinswere hardly detected in the paracrystalline prolamellar bodiesfrom Cucurbita etioplasts. We concluded that steroidal saponinsare not main building units of the prolamellar body in the etioplasts. (Received August 5, 1982; Accepted February 15, 1983)     

Glycoproteins of mouse zona pellucida: Analysis of their reactivity to lectins

Zonae pellucidae were isolated as an intact structure from superovulated mouse eggs using a new simplified method, and the proteins were fractionated by SDS-polyacrylamide gel electrophoresis. Location of proteins by silver stain showed three bands previously designated as ZP-1, ZP-2 and ZP-3. The reactivities of these proteins to specific lectins were examined after transferring them to nitrocellulose paper by the “Western” blotting technique. Ricinus communis agglutinin-I, Triticum vulgaris agglutinin, Dolichos biflorus agglutinin and Glycine max agglutinin reacted to all three zona proteins. However Concanavalin A reacted only to ZP-2 and Arachis hypogaea agglutinin only to ZP-1 and ZP-3. These results indicate that the carbohydrate of each zona protein is unique.     

Cysteine Sulfinic Acid in the Central Nervous System: Uptake and Release of Cysteine Sulfinic Acid by a Rat Brain Preparation

Abstract: Uptake and release of cysteine sulfinic acid by synaptosomal fractions (P₂) and slices of rat cerebral cortex were investigated. The P₂ fraction had a Na⁺-dependent high-affinity uptake system for cysteine sulfinic acid (K_m, 12μM), which was restricted to the synaptosomes. High-affinity uptake of cysteine sulfinic acid was competitively inhibited by glutamate, aspartate, and cysteic acid. None of the various centrally acting drugs tested specifically inhibited this transport system. Release of [¹⁴C]cysteine sulfinic acid from preloaded cortical slices or P₂ fractions was examined by a superfusion method, which avoided reuptake of released [¹⁴C]cysteine sulfinic acid. High K⁺ (56 m M ) and veratridine (10μM) stimulated the release of cysteine sulfinic acid from slices and the P₂ fraction in a partly Ca²⁺-dependent manner. Diazepam at concentrations of 10 and 100 μM markedly inhibited the stimulated release, but not the spontaneous release, by cortical slices. On the contrary, it had no effect on the stimulated release of cysteine sulfinic acid from the P₂ fraction.     

Phytoplankton photosynthesis in the subsurface chlorophyll-maximum layer of the tropical North Pacific Ocean

Maximum quantum yield (φ_m^B) and maximum photosynthetic rate (P_m^B) of light-saturation curves of phytoplankton photosynthesis were determined for nannoplankton (< 20 μm) and netplankton (>20 μm) from the subsurface chlorophyll-maximum layer at 14 stations in the tropical North Pacific Ocean in the spring of 1976. The maximum quantum yield $\text{(φ}{}_{\mathrm{m}}{}^{\mathrm{B}}\text{±}\text{s.e.}\text{)}$ was significantly higher for nannoplankton (0.056 ± 0.006 moles CO₂·Einstein^?1 absorbed) than netplankton (0.039 ± 0.002 moles CO₂·Einstein^?1 absorbed). The importance of nannoplankton in the maximum photosynthetic rate (P_m^B) appears to be less consistent. At least 60% of the theoretical maximum quantum yield (0.12 moles CO₂·Einstein^?1 absorbed) was probably incorporated into the particulate fraction at the subsurface chlorophyll-maximum layer.     

The glycine-rich sequence of the beta subunit of Escherichia coli H(+)-ATPase is important for activity

A short sequence motif rich in glycine residues, Gly-X-X-X-X-Gly-Lys-Thr/Ser, has been found in many nucleotide-binding proteins including the beta subunit of Escherichia coli H(+)-ATPase (Gly-Gly-Ala-Gly-Val-Gly-Lys-Thr, residues 149-156). The following mutations were introduced in this region of the cloned E. coli unc operon carried by a plasmid pBWU1: Ala-151----Pro or Val; insertion of a Gly residue between Lys-155 and Thr-156; and replacement of the region by the corresponding sequence of adenylate kinase (Gly-Gly-Pro-Gly-Ser-Gly-Lys-Gly-Thr) or p21 ras protein (ras) (Gly-Ala-Gly-Gly-Val-Gly-Lys-Ser). All F0F1 subunits were synthesized in the deletion strain of the unc operon-dependent on pBWU1 with mutations, and essentially the same amounts of H(+)-ATPase with these mutant beta subunits were found in membranes. The adenylate kinase and Gly insertion mutants showed no oxidative phosphorylation or ATPase activity, whereas the Pro-151 mutants had higher ATPase activity than the wild-type, and the Val-151 and ras mutants had significant activity. It is striking that the enzyme with the ras mutation (differing in three amino acids from the beta sequence) had about half the membrane ATPase activity of the wild-type. These results together with the simulated three-dimensional structures of the wild-type and mutant sequences suggest that in mutant beta subunits with no ATPase activity projection of Thr-156 residues was opposite to that in the wild-type, and that the size and direction of projection of residue 151 are important for the enzyme activity.     

Dopamine Inhibits Calcium-Independent γ-[3H]Aminobutyric Acid Release Induced by Kainate and High K+ in the Fish Retina

Kainic acid (KA) at micromolar concentrations stimulated the release of gamma-[3H]aminobutyric acid [( 3H]GABA) from a particulate fraction of the carp (Cyprinus carpio) retina. The KA action was dose-dependent but Ca2+-independent. A similar response was elicited by another glutamate receptor agonist, quisqualic acid, and high K+, but not by an aspartate agonist, N-methyl-D-aspartic acid. The stimulatory action of KA on the [3H]GABA release was selectively blocked by the KA blockers gamma-D-glutamylglycine and cis-2,3-piperidine dicarboxylic acid. Dopamine (DA), which is contained in DA interplexiform cells in the carp retina, inhibited the [3H]GABA release induced by KA and high K+ in a dose-dependent manner. 5-Hydroxytryptamine and two well-known GABA antagonists, bicuculline (Bic) and picrotoxin (Pic), also mimicked the DA effect on the GABA release at a comparable concentration. This inhibitory effect of DA as well as Bic and Pic on the [3H]GABA release evoked by KA was clearly antagonized by a DA blocker, haloperidol. The action of these agents (KA, DA, GABA antagonist) belonging to three different receptor categories on the GABAergic neurons (possibly external horizontal cells; H1 cells) is discussed in relation to other electrophysiological studies on the lateral spread of S-potentials between H1 cells.     

Apical Junctional Fluctuations Lead to Cell Flow while Maintaining Epithelial Integrity

Epithelial sheet integrity is robustly maintained during morphogenesis, which is essential to shape organs and embryos. While maintaining the planar monolayer in three-dimensional space, cells dynamically flow via rearranging their connections between each other. However, little is known about how cells maintain the plane sheet integrity in three-dimensional space and provide cell flow in the in-plane sheet. In this study, using a three-dimensional vertex model, we demonstrate that apical junctional fluctuations allow stable cell rearrangements while ensuring monolayer integrity. In addition to the fluctuations, direction-dependent contraction on the apical cell boundaries, which corresponds to forces from adherens junctions, induces cell flow in a definite direction. We compared the kinematic behaviors of this apical-force-driven cell flow with those of typical cell flow that is driven by forces generated on basal regions and revealed the characteristic differences between them. These differences can be used to distinguish the mechanism of epithelial cell flow observed in experiments, i.e., whether it is apical- or basal-force-driven. Our numerical simulations suggest that cells actively generate fluctuations and use them to regulate both epithelial integrity and plasticity during morphogenesis.