Degradation of Macromolecular Organic Compounds in a Tropical Lagoon (Ciénaga Grande,Colombia) and its Ecological Significance

Primary production and decomposition of organic substances were investigated in a tropical lagoon during the rainy season. Production and mineralization were measured using the oxygen method. Total bacteria numbers and biomasses were estimated with epifluorescence microscopy, and the enzymatic degradation capacity of model substrates was determined photometrically. These parameters were measured in the water and sediment of the lagoon itself and also in its effluents and incoming waters. The aim of the study was to determine the sites of highest microbial activity in the lagoon and to compare its activity with other coastal water bodies. Since the shallow water lagoon contains a large amount of particulate matter, it was of special interest to study the degradation of this material and its influence on the microbial population. It was found that up to 14 % of the bacteria colonized the particles and that 62 % of the respiration originated in the particle fraction >8 μm. Highest exoenzymatic activities were measured in the sediment and water of the mangrove belt. It is concluded that decomposition and conditioning of particulate organic matter play dominant roles in the recycling of organic carbon in the lagoon.     

Functional Cortical Network in Alpha Band Correlates with Social Bargaining

Solving demanding tasks requires fast and flexible coordination among different brain areas. Everyday examples of this are the social dilemmas in which goals tend to clash, requiring one to weigh alternative courses of action in limited time. In spite of this fact, there are few studies that directly address the dynamics of flexible brain network integration during social interaction. To study the preceding, we carried out EEG recordings while subjects played a repeated version of the Ultimatum Game in both human (social) and computer (non-social) conditions. We found phase synchrony (inter-site-phase-clustering) modulation in alpha band that was specific to the human condition and independent of power modulation. The strength and patterns of the inter-site-phase-clustering of the cortical networks were also modulated, and these modulations were mainly in frontal and parietal regions. Moreover, changes in the individuals’ alpha network structure correlated with the risk of the offers made only in social conditions. This correlation was independent of changes in power and inter-site-phase-clustering strength. Our results indicate that, when subjects believe they are participating in a social interaction, a specific modulation of functional cortical networks in alpha band takes place, suggesting that phase synchrony of alpha oscillations could serve as a mechanism by which different brain areas flexibly interact in order to adapt ongoing behavior in socially demanding contexts.     

Directed evolution of cellobiose utilization in Escherichia coli K12

The cellobiose catabolic system of Escherichia coli K12 is being used to study the role of cryptic genes in evolution of new functions. Escherichia coli does not use beta-glucoside sugars; however, mutations in several loci can activate the cryptic bgl operon and permit growth on the beta-glucoside sugars arbutin and salicin. Such Bgl+ mutants do not use cellobiose, which is the most common beta-glucoside in nature. We have isolated a Cel+ (cellobiose-utilizing) mutant from a Bgl+ mutant of E. coli K12. The Cel+ mutant grows well on cellobiose, arbutin, and salicin. Genes for utilization of these beta-glucosides are located at 37.8 min on the E. coli map. The genes of the bgl operon are not involved in cellobiose utilization. Introduction of a deletion covering bgl does not affect the ability to utilize cellobiose, arbutin, or salicin, indicating that the new Cel+ genes provide all three functions. Spontaneous cellobiose negative mutants also become arbutin and salicin negative. Analysis of beta-glucoside positive revertants of these mutants indicates that there are separate loci for utilization of each of the beta-glucoside sugars. The genes are closely linked and may be activated from a single locus. A fourth gene at an unknown location increases the growth rate on cellobiose. The cel genes constitute a second cryptic system for beta-glucoside utilization in E. coli K12.      

Study of the interaction of cadmium with membrane-bound succinate dehydrogenase

Cadmium ions inhibit membrane-bound succinate dehydrogenase with a second-order rate constant of 10.42 mM^–1s^–1 at pH 7.35 and 25°C. Succinate and malonate protect the enzyme against cadmium ion inhibition. The protection pattern exerted by succinate and malonate suggests that the group modified by cadmium is located at the active site. The pH curve of inactivation by Cd²⁺ indicates the involvement of an amino acid residue with pKa of 7.23.     

Neurabin/protein phosphatase-1 complex regulates dendritic spine morphogenesis and maturation

The majority of excitatory synapses in the mammalian brain form on filopodia and spines, actin-rich membrane protrusions present on neuronal dendrites. The biochemical events that induce filopodia and remodel these structures into dendritic spines remain poorly understood. Here, we show that the neuronal actin- and protein phosphatase-1-binding protein, neurabin-I, promotes filopodia in neurons and nonneuronal cells. Neurabin-I actin-binding domain bundled F-actin, promoted filopodia, and delayed the maturation of dendritic spines in cultured hippocampal neurons. In contrast, dimerization of neurabin-I via C-terminal coiled-coil domains and association of protein phosphatase-1 (PP1) with neurabin-I through a canonical KIXF motif inhibited filopodia. Furthermore, the expression of a neurabin-I polypeptide unable to bind PP1 delayed the maturation of neuronal filopodia into spines, reduced the synaptic targeting of AMPA-type glutamate (GluR1) receptors, and decreased AMPA receptor-mediated synaptic transmission. Reduction of endogenous neurabin levels by interference RNA (RNAi)-mediated knockdown also inhibited the surface expression of GluR1 receptors. Together, our studies suggested that disrupting the functions of a cytoskeletal neurabin/PP1 complex enhanced filopodia and impaired surface GluR1 expression in hippocampal neurons, thereby hindering the morphological and functional maturation of dendritic spines.     

Subcellular distribution of prostaglandin-E2 and prostaglandin-F2 alpha in atrial tissue from patients with mitral valve disease

The distribution of prostaglandin-E2 (PGE2) and prostaglandin-F2 alpha (PGF2 alpha) was studied in subcellular fractions isolated from homogenates of human atrial fresh tissue by differential centrifugation. Right and left atrial samples were excised from the same heart of six patients with mitral valve disease at the time of open heart surgery. The atrial fractions investigated were mitochondrial (8,500 g pellet), microsomal (100,000 g pellet) and cytosol soluble (100,000 g supernatant) fractions. After extraction of prostaglandins from the three atrial fractions and separation of PGE from PGF series by chromatography on silicic acid column, these prostaglandins were measured by radioimmunoassay. The results showed that PGE2 and PGF2 alpha were located mainly in the soluble cytosolic fraction of right and left atrial tissue (p < 0.001). Furthermore, the prostaglandins levels were higher in left than in right atria of these patients (p < 0.001). The relation between prostaglandins heart generation in response to elevated work load of mitral valve disease is discussed.     

Phenology of Gigartina skottsbergii (Gigartinaceae,Rhodophyta) in Ancud Bay,southern Chile

This study reports the variations in biomass and reproductive phenology in a natural bed of Gigartina skottsbergii over a period of a year and correlates these variations with the abiotic factors solar radiation, number of daylight hours, water temperature and salinity. The results obtained show an annual production cycle with maximum biomass values in spring-summer, correlated with high solar radiation and to a lesser extent with salinity. Sexual reproduction was maximum in autumn-winter, correlated with low temperature and short-day conditions. The population showed a large gametophytic dominance according to size and biomass, which suggests that there is not ecological equivalence between the life history phases of the species. Finally, based on the results, a restriction of harvesting to spring-summer is suggested.     

Crystal structure and statistical coupling analysis of highly glycosylated peroxidase from royal palm tree (Roystonea regia)

Royal palm tree peroxidase (RPTP) is a very stable enzyme in regards to acidity, temperature, H₂O₂, and organic solvents. Thus, RPTP is a promising candidate for developing H₂O₂-sensitive biosensors for diverse applications in industry and analytical chemistry. RPTP belongs to the family of class III secretory plant peroxidases, which include horseradish peroxidase isozyme C, soybean and peanut peroxidases. Here we report the X-ray structure of native RPTP isolated from royal palm tree (Roystonea regia) refined to a resolution of 1.85 Å. RPTP has the same overall folding pattern of the plant peroxidase superfamily, and it contains one heme group and two calcium-binding sites in similar locations. The three-dimensional structure of RPTP was solved for a hydroperoxide complex state, and it revealed a bound 2-(N-morpholino) ethanesulfonic acid molecule (MES) positioned at a putative substrate-binding secondary site. Nine N-glycosylation sites are clearly defined in the RPTP electron-density maps, revealing for the first time conformations of the glycan chains of this highly glycosylated enzyme. Furthermore, statistical coupling analysis (SCA) of the plant peroxidase superfamily was performed. This sequence-based method identified a set of evolutionarily conserved sites that mapped to regions surrounding the heme prosthetic group. The SCA matrix also predicted a set of energetically coupled residues that are involved in the maintenance of the structural folding of plant peroxidases. The combination of crystallographic data and SCA analysis provides information about the key structural elements that could contribute to explaining the unique stability of RPTP.     

Local sharing as a predominant determinant of synaptic matrix molecular dynamics

Recent studies suggest that central nervous system synapses can persist for weeks, months, perhaps lifetimes, yet little is known as to how synapses maintain their structural and functional characteristics for so long. As a step toward a better understanding of synaptic maintenance we examined the loss, redistribution, reincorporation, and replenishment dynamics of Synapsin I and ProSAP2/Shank3, prominent presynaptic and postsynaptic matrix molecules, respectively. Fluorescence recovery after photobleaching and photoactivation experiments revealed that both molecules are continuously lost from, redistributed among, and reincorporated into synaptic structures at time-scales of minutes to hours. Exchange rates were not affected by inhibiting protein synthesis or proteasome-mediated protein degradation, were accelerated by stimulation, and greatly exceeded rates of replenishment from somatic sources. These findings indicate that the dynamics of key synaptic matrix molecules may be dominated by local protein exchange and redistribution, whereas protein synthesis and degradation serve to maintain and regulate the sizes of local, shared pools of these proteins.