Assembly and disassembly of brain tubulin is affected by high ammonia levels

Rats were fed a diet containing ammonium for up to 6 months. High ammonia levels were attained in brain. The amount of polymerized tubulin in microtubules increased, while the amount of free tubulin remained unchanged. Polymerization of tubulin from brain of ammonium fed rats (30 min, 37°C) was approximately 60% of control. Depolymerization of the microtubules was also affected and took approximately 3 times longer than in controls. These results indicate that both assembly and disassembly of tubulin in brain are impaired by high ammonia levels. Interestingly, the amount of microtubule-associated proteins was not affected.     

Proteolytic stimulation and solubilization of membrane-bound acetylcholinesterase from muscle sarcotubular system

Incubation of membranes derived from sarcotubular system of rabbit skeletal muscle with increasing concentrations of Triton X-100 produced both stimulation of the AChE activity and solubilization of this enzyme. Mild proteolytic treatment of microsomal membranes produced a several fold activation of the still membrane-bound acetylcholinesterase (AChE) activity. Attempts were made to solubilize AChE from microsomal membranes by proteolytic treatment. About 30–40% of the total enzyme activity could be solubilized by means of trypsin or papain. Short trypsin treatment of the microsomal membranes produced first an activation of the membrane-bound enzyme followed by solubilization. Incubation of muscle microsomes for a short time with papain yielded a significant portion of soluble enzyme. Membrane-bound enzyme activation was measured after a prolonged incubation period. These results are compared with those of solubilization obtained by treatment of membranes with progressive concentrations of Triton X-100. The occurrence of molecular forms in protease-solubilized AChE was investigated by means of centrifugation analysis and slab gel electrophoresis. Centrifugation on sucrose gradients revealed two main components of 4.4S and 10–11S in either trypsin or papain-solubilized AChE. These components behaved as hydrophilic species whereas the Triton solubilized AChE showed an amphipatic character. Application of slab gel electrophoresis showed the occurrence of forms with molecular weights of 350,000; 175,000; 165,000; 85,000 and 76,000. The stimulation of membrane-bound AChE by detergents or proteases would indicate that most of the enzyme molecules or their active sites are sequestered into the lipid bilayer through lipid-protein or protein-protein interactions and these are broken by proteolytic digestion of the muscle microsomes.     

A protein-free diet changes synaptosomal membrane fluidity and tyrosine and glutamate transport

Synaptosomes were isolated from cerebrums of rats fed standard (20% protein) or protein-free diets for 30 days. Arrhenius plots of their (Na⁺/K⁺)ATPase activities revealed a transition temperature of 25.5°C for control rats and 23.4°C for rats on protein-free diet, indicating that the latter increases synaptosomal membrane fluidity. The only change observed in the composition of the synaptosomal membranes was a 26% decrease of sialic acid. In synaptosomes from rats on protein-free diet the uptake of tyrosine was slightly reduced while that of glutamate was not affected. However, the exit of glutamate was reduced.     

Fine needle aspiration of peripheral neuroepithelioma of soft tissues.

Peripheral neuroepithelioma of soft tissue is a malignant primitive neuroectodermal tumor that appears both in children and adults and usually has a poor outcome. Fine needle aspiration on two patients with tumors in the lower limbs showed small round cells with unipolar processes and a tendency to form Homer-Wright rosettes. The cells had a round to oval nucleus with fine chromatin, up to four small, conspicuous nucleoli and vacuolated, periodic acid-Schiff-positive cytoplasm. The diagnosis was supported by electron microscopic study of the aspirate, which showed features of neuroblastic differentiation (i.e., neurosecretory granules), and by histologic, immunohistochemical and cytogenetic study of the resected tumors.     

Biological basis for the management of ‘lugs negra’ (Sarcothalia crispata Gigartinales,Rhodophyta) in southern Chile

The present paper describes growth dynamics in a natural bed of the resource luga negra (Sarcothalia crispata) in Guapilinao, southern Chile (41°57 S, 73°31 W). This resource is currently harvested and exported as raw material for the production of carrageenan. Seasonal variation in biomass, frond size, density and phenology was determined by periodic sampling. Natural recruitment was evaluated on different substrata added to the field; at the same time, substrata were inoculated under greenhouse conditions. Results showed that luga negra has seasonal growth: biomass increased from a minimum in spring to a maximum in mid to late summer. On the other hand, density was minimal in winter (200 ind. m^–2) and increased to 2000 ind. m^–2 in late spring. Peak abundance of mature tetrasporic fronds occurred in late summer, whereas that of cystocarpic fronds occurred in winter. Recruitment began in summer and extended into winter. Survival on different substrata were compared. Gametophytes had better survival rates on clam shells and 5 mm rope while tetrasporophytes had the best survival rate on clam shells and secondarily on boulders.     

Effects of the diatom-Emiliana huxleyi succession on photosynthesis, calcification and carbon metabolism by size-fractioned phytoplankton

Changes in the species composition, photosynthesis, calcification and size-fractionated carbon metabolism by natural phytoplankton assemblages were monitored in three mesocosms under different nutrient conditions during May 1993. In the 3 enclosures, the decline of the diatom-dominated assemblages was followed by the development of a bloom of the coccolithoporid Emiliania huxleyi. Highest growth of E. huxleyi was observed in the mesocosm with a high N : P ratio, suggesting this species is a good competitor at low phosphate concentrations. The transition from diatom- to E. huxleyi-dominated assemblages brought about a sharp reduction of the phytoplankton standing stock and carbon-specific photosynthetic rate. The relative contribution of the smaller size fraction to total photosynthesis increased as the succession progressed. Calcification rate and E. huxleyi cell-specified calcite production were highest during the early stages of development of the E. huxleyi bloom. Distinct changes in the patterns of ¹⁴C allocation into biomolecules were noticed during the diatom-E. huxleyi succession. The diatom-dominated assemblage showed high relative ¹⁴C incorporation into low molecular weight metabolites (LMWM), whereas proteins and, specially, lipids accounted for the largest proportion of carbon incorporation in the E. huxleyi bloom. The patterns of photoassimilated carbon metabolism proved to be strongly dependent on cellular size, as protein relative synthesis was significantly higher in the smaller than in the larger size fraction, irrespective of the nutrient regime and the successional stage. These results are discussed in relation to the ecological and physiological features of small phytoplankton.     

Phytoplankton biomass and production in shelf waters off NW Spain: spatial and seasonal variability in relation to upwelling

Summary Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied at 125 stations between 1984 and 1992. Three geographic areas (Cantabrian Sea, Rías Altas and Was Baixas), three bathymetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and four oceanographic stages (spring and autumn blooms, summer upwelling, summer stratification and winter mixing) were considered. One of the major sources of variability of chlorophyll and production data was season. Bloom and summer upwelling stages have equivalent mean and maximum values. Average chlorophyll-a concentrations approximately doubled in every step of the increasing productivity sequence: winter mixing — summer stratification — high productivity (upwelling and bloom) stages. Average primary production rates increased only 60% in the described sequence. Mean (± sd) values of chlorophyll-a and primary production rates during the high productivity stages were 59.7 ± 39.5 mg Chl-a m^–2 and 86.9 ± 44.0 mg C m^–2 h^–1, respectively. Significant differences in both chlorophyll and primary production resulted between geographic areas in most stages. Only 27 stations showed the effects of the summer upwelling that affected coastal areas in the Cantabrian Sea and Rías Baixas shelf, but also shelf-break stations in the Rías Altas area. The Rías Baixas area had lower chlorophyll than both the Rías Altas and the Cantabrian Sea areas during spring and autumn blooms, but higher during summer upwelling events. On the contrary, primary production rates were higher in the Rías Baixas area during blooms in spring and autumn. Mid-shelf areas showed the highest chlorophyll concentrations during high productivity stages, probably due to the existence of frontal zones in all geographic areas considered. The estimated phytoplankton growth rates were comparable to those of other coastal upwelling systems, with average values lower than the maximum potential growth rates. Doubling rates for upwelling and stratification stages in the northern and Rías Altas shelf areas were equivalent, despite larger biomass accumulations during upwelling events. Low turnover rates of the existing biomass in the Rías Baixas shelf in upwelling stages suggests that the accumulation of phytoplankton was due mainly to the export from the highly productive rías, while the contribution of in situ production to these accumulations was relatively lower.