Developmental Pattern for Phosphatidylserine Decarboxylase in Rat Brain

In adult rats, a significant portion of brain ethanolamine glycerophospholipids are synthesized by a pathway involving phosphatidylserine decarboxylase, a mitochondrial enzyme. We have now examined whether this enzyme plays a particularly prominent role during development. Activities for both phosphatidylserine decarboxylase and succinate dehydrogenase (another mitochondrial enzyme) were determined in brain homogenates from rats 5 days of age to adulthood. Succinate dehydrogenase activity, expressed on a per unit brain protein basis, increased markedly during development. This pattern has been reported previously and is as expected from the postnatal increase in oxidative metabolism. In contrast, phosphatidylserine decarboxylase activity decreased 40% from 5 to 30 days of age. The apparent Km for brain phosphatidylserine decarboxylase was 85 microM in both young (8- and 20-day-old) and adult animals. Parallel studies in vivo were carried out to determine the contribution of the phosphatidylserine decarboxylase pathway, relative to pathways utilizing ethanolamine directly, to the synthesis of brain ethanolamine glycerophospholipids. Animals were injected intracranially with a mixture of L-[G-3H]serine and [2-14C]ethanolamine and incorporation into the base moieties of the phospholipids determined. The 3H/14C ratio of ethanolamine glycerophospholipids decreased about 50% during development. Our studies in vitro and in vivo both suggest that phosphatidylserine decarboxylase plays a significant role in the synthesis of brain ethanolamine glycerophospholipids at all ages, although it is relatively more prominent early in development.     

The kinetics and reaction mechanism of the nicotinamide-adenine dinucleotide phosphate-specific glycerol dehydrogenase of rat skeletal muscle

The NADP-specific glycerol dehydrogenase of rat skeletal muscle has been partially purified by ammonium sulphate fractionation. The enzyme has been studied kinetically by initial-velocity analysis, product inhibition and inhibition by fluoride. The experimental results indicate that the reaction mechanism for the enzyme is ordered such that the first product leaves the enzyme before the addition of the second substrate.     

Lysophosphatidic acid enhances contractility of isolated airway smooth muscle

Toews, M. L., E. E. Ustinova, and H. D. Schultz.Lysophosphatidic acid enhances contractility of isolated airwaysmooth muscle. J. Appl. Physiol.83(4): 1216-1222, 1997.The effects of the simple phospholipidmediator lysophosphatidic acid (LPA) on the contractile responsivenessof isolated tracheal rings from rabbits and cats were assessed. In bothspecies, LPA increased the contractile response to the muscarinicagonist methacholine, but LPA did not induce contraction on its own.Conversely, LPA decreased the relaxation response to the-adrenergic-agonist isoproterenol in both species. Concentrations ofLPA as low as 10⁸ M wereeffective, and the effects of LPA were rapidly reversed on washing.Phosphatidic acid was much less effective, requiring higherconcentrations and producing only a minimal effect. Contractions induced by serotonin and by substance P also were enhanced by LPA, butKCl-induced contractions were unaffected. LPA inhibited theisoproterenol-induced relaxation of KCl-precontracted rings, similar toits effects on methacholine-precontracted rings, and relaxation inducedby the direct adenylyl cyclase activator forskolin was inhibited in amanner similar to that induced by isoproterenol. Epithelium removal didnot alter the contraction-enhancing effect of LPA. The ability of LPAto both enhance contraction and inhibit relaxation of airway smoothmuscle suggests that LPA could contribute to airway hypercontractilityin asthma, airway inflammation, or other types of lung injury.

     

The hypolimnetic protozoan plankton of a eutrophic lake

The seasonal distribution of benthic species in the water column above and below the thermocline in a small eutrophic lake is described. During summer stratification populations of Spirostomum spp, Loxodes spp., Plagiopyla and Deltopylum become established in the plankton on or below the oxycline/thermocline. At shallow sites no migration occurred and populations of the migratory species in the benthos were sparse, with the exception of Plagiopyla which occurred in high densities in the sediment. Two distinct planktonic populations are established during stratification: an epilimnetic community of obligate planktonic ciliates and a hypolimnetic community of benthic migrants.     

Axonal Transport and Metabolism of Glycoproteins in Rat Sciatic Nerve

The distribution of 5'-nucleotidase activity, dopaminergic [3H]spiperone binding sites, and [3H]quinuclidinyl benzilate (QNB) binding sites in different subcellular fractions of bovine caudate nucleus has been studied. Each activity was enriched in a microsomal (P3) preparation from that tissue. The microsomal preparation was further fractionated by different techniques. First, the P3 fraction, or a sonicated P3 fraction, was fractionated on a discontinuous sucrose density gradient. Second, the P3 fraction, or a digitonin pretreated P3 fraction, was fractionated on a continuous sucrose density gradient. The results obtained demonstrate that 5'-nucleotidase activity does not cofractionate with radioligand binding activity, although no difference between the distributions of [3H]spiperone binding and [3H]QNB binding were seen. It is concluded that the two radioligand binding activities are located on nonglial membranes.     

A kinetic study of pig liver glucose dehydrogenase.

Utilizing a temperature-sensitive mutant of Escherichia coli K-12 defective in the coupling of metabolic energy to active transport, we have demonstrated that the uptake systems for arabinose, galactose, valine, histidine, and glutamine, which are sensitive to the osmotic shock treatment of L. A. Heppel (1965) (J. Biol. Chem.240, 3685), are all totally defective at the nonpermissive temperature (42 °C) whereas the intracellular ATP levels increase twofold. Phosphate bond energy alone is therefore not sufficient to energize the transport of these substrates. We have confirmed the findings of E. A., Berger and L. A. Heppel (1974) (J. Biol. Chem. 249, 7747) regarding a severe arsenate I inhibition of the uptake of substrates belonging to osmotic shock-sensitive transport systems and therefore conclude that both ATP and a functional ecf gene product are required for the coupling of energy to the transport of these solutes.     

A mathematical model of avian influenza with half-saturated incidence

The widespread impact of avian influenza viruses not only poses risks to birds, but also to humans. The viruses spread from birds to humans and from human to human In addition, mutation in the primary strain will increase the infectiousness of avian influenza. We developed a mathematical model of avian influenza for both bird and human populations. The effect of half-saturated incidence on transmission dynamics of the disease is investigated. The half-saturation constants determine the levels at which birds and humans contract avian influenza. To prevent the spread of avian influenza, the associated half-saturation constants must be increased, especially the half-saturation constant H _m for humans with mutant strain. The quantity H _m plays an essential role in determining the basic reproduction number of this model. Furthermore, by decreasing the rate β _m at which human-to-human mutant influenza is contracted, an outbreak can be controlled more effectively. To combat the outbreak, we propose both pharmaceutical (vaccination) and non-pharmaceutical (personal protection and isolation) control methods to reduce the transmission of avian influenza. Vaccination and personal protection will decrease β _m, while isolation will increase H _m. Numerical simulations demonstrate that all proposed control strategies will lead to disease eradication; however, if we only employ vaccination, it will require slightly longer to eradicate the disease than only applying non-pharmaceutical or a combination of pharmaceutical and non-pharmaceutical control methods. In conclusion, it is important to adopt a combination of control methods to fight an avian influenza outbreak.     

Outdoor flight activity and immigration of Rhyzopertha dominica into seed wheat warehouses

The flight activity of lesser grain borer, Rhyzopertha dominica F. (Coleoptera: Bostrichidae), was monitored at two Foundation seed wheat warehouses during the 2003 and 2004 field seasons, using pheromone‐baited Lindgren funnel traps positioned indoors and outdoors. General stored‐product insect activity was also monitored using unbaited sticky traps positioned inside the warehouses around overhead doors. Pheromone‐baited traps were useful for monitoring R. dominica activity, however insect captures decreased when lures were not changed weekly. Flight peaks were documented in early May and again from September through October, and insect captures inside warehouses correlated with timing of outdoor captures. Multiple regression analyses showed that slightly more than half of the variability in R. dominica captures could be explained by mean ambient air temperature and wind speed during the 2 h preceding sunset. Stored‐product Coleoptera captured on unbaited glue boards around overhead doors included Ahasverus advena, Cryptolestes ferrugineus, R. dominica, Sitophilus oryzae, Tribolium castaneum, Trogoderma variabile, and Typhaea stercorea. Door gaskets significantly reduced the number of insect captures on glue boards placed around the overhead doors, and generally restricted their entry to ground level. These studies demonstrated that outdoor pheromone‐baited traps are effective monitoring tools for determining when grain‐handling facilities are most susceptible to infestation and that exclusion may be an effective component of a pest management program.