The ideal hydrodynamic form of the concavo‐convex productide brachiopod shell

Shiino, Y & Suzuki, Y. 2011: The ideal hydrodynamic form of the concavo‐convex productide brachiopod shell. Lethaia, Vol. 44, pp. 329–343. Water‐flume experiments were performed to determine whether the concavo‐convex Permian brachiopod Waagenoconcha imperfecta was hydrodynamically adapted for feeding. The generation of passive currents inside the valves was observed experimentally. The use of four transparent, hollow polyhedron models, each differing in a single morphological feature, permitted observation of the currents inside the valves and allowed evaluation of the hydrodynamic significance of the ears and the prominent geniculated trail. Regardless of the direction of ambient flow, only the approximate‐imitation model generated a stable flow pattern consisting of inhalation from the ear gapes and exhalation from the anterior trail gape; models lacking or with small changes in these morphological features failed to generate stable flow patterns. The stable flow pattern was probably maintained by a pressure difference between the posterior lower ear gapes (maximum pressure) and the anterior trail gape (minimum pressure). Notably, bilaterally rotating internal currents formed parallel to the brachial ridges; such flow patterns would facilitate the capture of food particles by the animal via tentacles on its lophophore, which is most likely were located on the brachial ridges. Our results demonstrate that the immobile brachiopod W. imperfecta, an animal incapable of widely opening its valves, probably fed on the passive internal currents generated by its shell form. This unique valve morphology appears to be perfectly adapted from a hydrodynamic point of view. □Biomechanics, ecomorphology, evolution, morphological disparity, Productidina, suspension feeder.     

Melanin Granules Prevent the Cytotoxic Effects of l‐DOPA on Retinal Pigment Epithelial Cells in Vitro by Regulation of NO and Superoxide Radicals

Inasmuch as the nitrogen cycle elicits the direct reduction of N₂ to NH₃ through enzymatic reactions, and inasmuch as l ‐DOPA ( l ‐dihydroxyphentlalamine), a catecholamine, can be a source of nitric oxide (NO), it is possible that melanin granules in the eye affect the generation of NO, which causes damage to the retinal pigment epithelial (RPE) cells during the oxidation of l ‐DOPA. In order to confirm this possibility, we analyzed the correlations of NO generation, cell growth, and superoxide dismutase (SOD) activities in two types (melanotic and amelanotic) of bovine RPE cells following exposure to l ‐DOPA. NO generation from l ‐DOPA was determined using an NO detector that is reliant on redox currents. The concentration of NO was measured in terms of diffusion currents run between a working electrode and a counter electrode, both being set in culture medium placed in a Petri dish. For the assays, l ‐DOPA was added to the medium at various concentrations (5, 29.9, 79.4, 152.7 or 249 μM), and 6 min after addition, an NO‐trapping agent 2,4‐carboxyphenyl‐4,4,5,5‐tetramethylimidazole‐1‐oxyl 3‐oxide (carboxy‐PTIO) was also added. The melanotic and amelanotic types of RPE cells were cultured separately in medium with l ‐DOPA under an atmosphere containing 20, 10 or 5% oxygen. Cell numbers were counted using a Coulter counter, and SOD activities were determined following incubation for 24, 48 or 72 hr using a modification of the luminol assay. The results obtained indicated that: (a) NO was produced from l ‐DOPA in a concentration‐dependent manner and was trapped quantitatively by carboxy‐PTIO; (b) the generation of NO was inhibited more markedly in the melanotic cell line than in the amelanotic one, suggesting an increased tolerance to l ‐DOPA‐derived cytotoxicity in the former; and (c) the SOD activities were more affected by oxygen concentration in the melanotic cells than in the amelanotic ones. From these results, it is concluded that melanin granules in RPE cells have a role in preventing the cytotoxicity derived from l ‐DOPA and in regulating the generation of NO and superoxide radicals.     

FLAVOPROTEINS IN THE LEAVES OF HIGHER PLANTS CATALYZING THE OXIDATION OF L-GLUTAMATE

1. Two forms of enzyme capable of catalyzing the oxidation of L-glutamate(and L-aspartate) were isolated from the leaves of spinach andseparated from each other by column-chromatographic purificationon calcium phosphate and anion exchangers. They were distinguishedas GD₁ (L-glutamate dehydrogenase 1) and GD₂ (L-glutamate dehydrogenase2). The purification procedures and some fundamental propertiesof the partially purified enzymes were investigated.
2. It wasdiscovered that the enzymes did not require any cofactor,ie., neither dialysis nor precipitation with ammonium sulfatecaused a fall in enzyme activities and the addition of DPN andTPN to the reaction mixture did not accelerate the reactionrate
3. From the results of spectroscopic investigation GD₁ andGD₂were shown to be flavoproteins, although their prostheticgrouphas not yet been identified The activity of GD₁ was enhancedby the addition of FAD or FMN, while GD₂ was not acceleratedby these factors.
4. The characteristics of the two enzymes includingsubstrate specificity,MICHAELIS constant, optimum pH of thereaction and specificityfor electron acceptors were compared.
5. From the stoichiometric study of the oxidation of L-glutamatewith these enzymes, it was confirmed that the reaction is representedby the following equation: L-glutamate+oxidized dye+h₂o
6. Among various inhibitors tested,molecular oxygen which couldfunction as electron acceptor ofL-glutamate oxidation in thepresence of GD₁ was found to causea strong inhibition uponthe same reaction with TTC as el acceptor.The inhibition wasconfirmed to be due to hydrogen peroxideproduced as a resultof the aerobic oxidation of L-glutamate.

(Received July 25, 1962; )     

Reductive carboxylation and amination of keto acids by spinach chloroplasts

1. In spinach chloroplasts, the occurrence of malic enzyme,isocitrate dehydrogenase, glutamate dehydrogenase and alaninedehydrogenase was confirmed. 2. In the presence of ammonia, pyruvate and -ketoglutarate andpyruvate were photoreductively aminated to glutamate and alanine,respectively. 3. In the absence of ammonia, pyruvate and -ketoglutarate werephotoreductively carboxylated to malate and isocitrate, respectively. 4. Photoreductive carboxylation of pyruvate and -ketoglutaratewas suppressed by molecular oxygen. Inhibition was partly dueto oxidation of photoreduced NADP or NAD. (Received August 4, 1969; )     

Amino-acid Sequence of λ Phage Endolysin

WE wish to present a preliminary report of the amino-acid sequence of λ endolysin. This protein is a lytic enzyme¹ and its structural gene, R, maps toward the right end of λ DNA². Conditional mutants as well as frame-shift mutants (R. Thomas, personal communication) have been isolated and analysed³. Hogness et al.⁴ developed a technique to assay the gene activity of the fragmented λ DNA, which suggested that it might be possible to isolate a small segment of DNA containing the endolysin gene. Purification, immunological properties and end group analysis of λ endolysin were studied by Black and Hogness^5–7.     

Prothoracicotropic Hormone Bioassay: Pupal-Adult Bombyx Assay

Blockage of adult development by brain removal and its resumption by application of the prothoracicotropic hormone (PTTH) were studied using pupae of a racial hybrid J-122 × C-115 of Bombyx mori . A log-linear dose-response relationship was obrained after injection of a PTTH solution. The Bombyx -unit of PTTH has been defined from this dose-response curve.     

ON THE NATURE OF MOSS OXALIC ACID OXIDASE

Moss oxalic acid oxidase freed from catalase by boiling is stronglyinhibited by the "metal-complexing" compounds such as thiocyanate,azide, diethyldithiocarbamate, and hydrosulfite. Inactivatedby dialysis against thiocyanate or azide, the enzyme can bereactivated to a considerable extent by the addition of ferricsalt, cytochrome-c or hemoglobin, not by other metal ions, suchas Cu²⁺, Zn²⁺ , Mn²⁺, and Fe²⁺. Nitrate, chlorate, monoiodoacetate,and iodide also act as strong inhibitors towards moss oxalicacid oxidase. Some enzyme fractions which were obtained by the sodium sulfateprecipitation method were stimulated by Fe³⁺, but not by cytochrome-cor by other metallic ions. This stimulation was inhibited bythiocyanate, azide and monoiodoacetate. ¹ Present address: Biological Institute, University of Toyama,Toyama     

THE DISTRIBUTION OF FORMYLTETRAHYDROFOLATE SYNTHETASE IN PLANTS, AND THE PURIFICATION AND PROPERTIES OF THE ENZYME FROM PEA SEEDLINGS

1. Formyltetrahydrofolate synthetase (E. C. 6. 3. 4. 3) was foundto be widely distributed in higher plants and the high enzymeactivity was observed in green leaves of Brassica and Alliumspecies, spinach, and in pea seedlings. In pea seedlings, theenzyme activity changed during the course of germination, andmost of the enzyme activity was located in a soluble fractionof the cytoplasm.
2. The enzyme was labile and lost the activityrapidly, even whenstored at 5 in the presence of 0.1 M mercaptoethanol.It was,however, found that ammonium sulfate was very effectivein stabilizingthe enzyme activity.
3. The enzyme has been purifiedapproximately 500-fold from extractsof pea seedlings by treatmentswith ammonium sulfate, protaminesulfate, hydroxylapatite, calciumphosphate gel, and DEAE-cellulosecolumn chromatography.
4. Thepurified enzyme was specific for formate, ATP and FAH₄,andthe Michaelis constants for these reactants were 2.1 10^–2M, 5.1 10^–4 M, and 5.6 10^–3 M, respectively.
5. The optimum pH was found to be 8.0, and the optimal temperaturewas observed at 37. Both NH₄^$ and a divalent cation (Mg^SS orMn^SS) were required for the optimal activity.

¹ Studies on the Enzymatic Synthesis and Metabolism of FolateCoenzymes in Plants. II. (For the previous paper see reference(8)) A part of this paper was presented at the Meeting of theKansai Division of the Agricultural Chemical Society of Japan,Kyoto, January 29, 1966.