Yellow Pellets Research Articles

Understanding phospholipid function: Why are there so many lipids?

In the 1970s, phospholipids were still considered mere building blocks of the membrane lipid bilayer, but the subsequent realization that phospholipids could also serve as second messengers brought new interest to the field. My own passion for the unique amphipathic properties of lipids led me to seek other, non-signaling functions for phospholipids, particularly in their interactions with membrane proteins. This seemed to be the last frontier in protein chemistry and enzymology to be conquered. I was fortunate to find my way to Eugene Kennedy's laboratory, where both membrane proteins and phospholipids were the foci of study, thus providing a jumping-off point for advancing our fundamental understanding of lipid synthesis, membrane protein biosynthesis, phospholipid and membrane protein trafficking, and the cellular roles of phospholipids. After purifying and characterizing enzymes of phospholipid biosynthesis in Escherichia coli and cloning of several of the genes encoding these enzymes in E. coli and Saccharomyces cerevisiae, I was in a position to alter phospholipid composition in a systematic manner during the cell cycle in these microorganisms. My group was able to establish, contrary to common assumption (derived from the fact that membrane proteins retain activity in detergent extracts) that phospholipid environment is a strong determining factor in the function of membrane proteins. We showed that molecular genetic alterations in membrane lipid composition result in many phenotypes, and uncovered direct lipid-protein interactions that govern dynamic structural and functional properties of membrane proteins. Here I present my personal "reflections" on how our understanding of phospholipid functions has evolved.

Cadmium, lead and bromine in beached microplastics

Samples of microplastic (n = 924) from two beaches in south west England have been analysed by field-portable-x-ray fluorescence (FP-XRF) spectrometry, configured in a low-density mode and with a small-spot facility, for the heavy metals, Cd and Pb, and the halogen, Br. Primary plastics in the form of pre-production pellets were the principal type of microplastic (>70%) on both beaches, with secondary, irregularly-shaped fragments representing the remainder of samples. Cadmium and Pb were detected in 6.9% and 7.5% of all microplastics, respectively, with concentrations of either metal that exceeded 103 μg g−1 usually encountered in red and yellow pellets or fragments. Respective correlations of Cd and Pb with Se and Cr were attributed to the presence of the coloured, inorganic pigments, cadmium sulphoselenide and lead chromate. Bromine, detected in 10.4% of microplastics and up to concentrations of about 13,000 μg g−1, was mainly encountered in neutrally-coloured pellets. Its strong correlation with Sb, whose oxides are effective fire suppressant synergists, suggests the presence of a variety of brominated flame retardants arising from the recycling of plastics originally used in casings for heat-generating electrical equipment. The maximum bioaccessible concentrations of Cd and Pb, evaluated using a physiological extraction based on the chemical characteristics of the proventriculus-gizzard of the northern fulmar, were about 50 μg g−1 and 8 μg g−1, respectively. These concentrations exceed those estimated for the diet of local seabirds by factors of about 50 and 4, respectively.

An analysis of avoidance generalization and food preference transitivity in goldfish, Carassius auratus

To examine the effect of novelty in food selection by fishes, goldfish were trained by feeding them on red or green food pellets. Individual fish and fish in shoals of two, three, and five were then given a choice between equal numbers of familiar pellets and novel (yellow) pellets. In experimental groups, the yellow pellets were soaked in 15% quinine hydrochloride to make them unpalatable. Fish were next presented with equal numbers of familiar and a second novel pellet. It was expected that fish would generalize from their experience with the unpalatable pellets and demonstrate avoidance to sampling a second novel food item. However, as groups, neither controls nor experimentals were reluctant to sample the second novel pellets. Also, fish did not eat significantly more familiar than novel pellets when both were palatable. A third set of experiments examined food preference transitivity in which each pellet type was presented alone and in three pair-wise combinations to individual fish. Although red and yellow pellets were preferred over green, they were preferred equally, indicating an absence of transitivity in pellet choice and, perhaps, a “preference” for a mixture of red and yellow pellets.

Characterization of fatty acids and proteins associated with the xanthophyll-enriched membrane fraction isolated from the thylakoid membranes of irradiance-stressed Dunaliella salina

It has been previously reported that a considerable amount of lutein and zeaxanthin could be fractionated, upon mild detergent treatment, from the thylakoid membranes of irradiance-stressed unicellular green alga, Dunaliella salina, into a yellow pellet fraction. Such membrane pellet was found to be devoid of chlorophylls and any known proteins of photosynthesis but rather contained a significant amount of unknown polypeptides. It was speculated that this xanthophyll-rich membrane pellet might originate from incomplete solubilization of the photoinhibited thylakoids by weak surfactants, due to extra rigidity imposed by the xanthophylls being directly imbedded into the lipid bilayer. In this study, we further characterized this membrane fraction by studying its associated proteins and fatty acid composition. Analysis by gas chromatography–mass spectrometry indicated that this yellow pellet membrane was enriched in saturated fatty acids, supporting the rigidity notion of the pellet. Protein identification by MALDI-TOF MS further revealed that at least 20 water-soluble proteins were found in association with this pellet. These proteins may originate from unspecific contamination of abundant polypeptides co-precipitated with the membrane upon fractionation. Possible explanations regarding the nature of this xanthophyll-rich membrane are also discussed.

Role of excreta in predator avoidance by the Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae)

The Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae) constructs webs over leaf surfaces and usually lives under these webs. T. kanzawai produces two types of excreta, black and yellow pellets, and uses its webs as a place for excretion. T. kanzawai also uses its webs as a refuge when the predatory mite, Neoseiulus womersleyi (Acari: Phytoseiidae) is present. To clarify what factors deter N. womersleyi from foraging on T. kanzawai webs, I experimentally examined the effects of T. kanzawai excreta on its own fitness (fecundity) and the foraging behaviour of N. womersleyi. When the excreta of T. kanzawai was put on leaf surfaces, the fecundity of T. kanzawai adult females was reduced by the black but not the yellow faecal pellets. On the other hand, predation by N. womersleyi was reduced by the yellow but not the black pellets. Although this effect of the yellow pellets on N. womersleyi did not last on leaf surfaces, it deterred N. womersleyi from staying on the web regardless of its freshness. These results suggest that T. kanzawai deposits black pellets on webs to avoid its negative effect on their own fitness, and yellow pellets are deposited on webs to reduce the risk of predation.

ADP Competes with FAD Binding in Putrescine Oxidase

Putrescine oxidase from Rhodococcus erythropolis NCIMB 11540 (PuO(Rh)) is a soluble homodimeric flavoprotein of 100 kDa, which catalyzes the oxidative deamination of putrescine and some other aliphatic amines. The initial characterization of PuO(Rh) uncovered an intriguing feature: the enzyme appeared to contain only one noncovalently bound FAD cofactor per dimer. Here we show that this low FAD/protein ratio is the result of tight binding of ADP, thereby competing with FAD binding. MS analysis revealed that the enzyme is isolated as a mixture of dimers containing two molecules of FAD, two molecules ADP, or one FAD and one ADP molecule. In addition, based on a structural model of PuO(Rh) that was built using the crystal structure of human monoamine oxidase B (MAO-B), we constructed an active mutant enzyme, PuO(Rh) A394C, that contains covalently bound FAD. These findings show that the covalent FAD-protein linkage can be formed autocatalytically and hint to a new-found rationale for covalent flavinylation: covalent flavinylation may have evolved to prevent binding of ADP or related cellular compounds, which would prohibit formation of flavinylated and functional enzyme.

Colour preferences and coloured bait consumption by weka Gallirallus australis, an endemic New Zealand rail

Native birds are among the non-target species that are killed in poisoning operations directed at introduced mammalian pests in New Zealand. By identifying colours that birds find unattractive, and incorporating them into poisonous baits, some deaths may be avoided. The colour preferences of weka, Gallirallus australis, an endemic New Zealand rail, were tested over 6 days by offering individual weka a choice between six different colours of a novel food pellet. Weka ate significantly more red and yellow pellets on the first day than green, mid-blue, light-blue, or brown pellets but consumption of all colours increased sharply on subsequent days. The colour preferences found agree well with published studies on other bird species. If colour preferences are general across species colour may be useful in deterring birds from poisonous baits. Weka however with their opportunistic and adaptable feeding style rapidly increased their consumption of baits, even those colours they initially avoided. It appears that a more active deterrent than colour will be needed for weka.

Increased Growth Rate in Atlantic Salmon Parr (Salmo salar) by Using a Two-Coloured Diet

Fishes hunting by sight are known to pay a cost of confusion when faced with high densities of uniform food particles. Factors such as swarm size, density, and visual uniformity increase confusion. Therefore, it may be profitable in pisciculture to introduce food particles in low densities or to reduce the uniformity and density of each type of feed pellet. This was tested by feeding Atlantic salmon parr (Salmo salar) brown pellets, yellow pellets, or a mixed diet. Mean growth rates were significantly higher for those fish fed a mixed diet. Of the smaller fish in all groups, those in the mixed diet group showed the highest weight/length ratio. We suggest that small individuals have to pay more attention to conspecifics than do large ones, and thus tolerate less confusion when feeding. Larger individuals, tolerating higher confusion costs, achieve higher feeding rates in high densities of uniform feed pellets.

Distribution and immunochemical properties of rat kidney l-amino-acid oxidase, with a note on peroxisomes

An amino-acid oxidase in rat kidney cells has been located mainly in peroxisomes and the soluble fraction. The peroxisomes were isolated as a bright yellow pellet from the fraction comprising mitochondria and light mitochondria by sucrose density gradient centrifugation. The particles contained l-amino acid oxidase in the ratio to total peroxisomal protein of 1:4 The enzyme in the subcellular particles could be easily solubilized by treatment with Triton X-100 without causing inactivation or immunochemical changes. The enzyme was found to be essentially the same in all subcellular fractions, as judged by the immunochemical studies and electrophoretic data. No enzyme which catalyzes the dehydrogenation of l-lactate or l-a- hydroxyisocaproate without added NAD + or flavin cofactors, other than l-amino-acid oxidase, was present in the rat kidney cells. The soluble fraction in rat kidney cells contained an unknown dialyzable activator of l amino acid oxidase.

Russellite, a new British mineral

In May, 1936, a quantity of pale yellow, rounded fragments, averaging 7 mm. across, was submitted to us by Mr. Arthur Russell for examination, with the information that the material came from the Castle-an-Dinas wolfram mine, and contained bismuth and tungsten. Chemical and spectroscopic examination showed that, besides bismuth and tungsten, the mineral contained only traces of silicon, arsenic, and iron. A sample of the same material had also been given to the British Museum by Mr. E. H. Davison in 1934 and registered provisionally as bismuth tungstate. This, however, would not have provided sufficient of the yellow mineral for chemical analysis. We are also indebted to Mr. Davison for a further generous supply of yellow pellets picked from the wolfram concentrates received since tile present work was begun. The mineral has all the attributes of an alteration product probably of native bismuth. It is fine-grained and compact, with hardness 3½, and on fracture it gives a clay-like odour. Some of the pellets show traces of a micaeeous mineral and quite frequently enclose native bismuth, wolframite, and bismuthinite. Mr. Russell has picked out from tihe material he had collected a few green pellets and some showing both the yellow and the green mineral. Spectrographs of the two are identical, but an X-ray powder photograph of the green mineral is quite distinct from that of tile yellow mineral.