Overexpression of proteins containing tyrosine- or leucine-based sorting signals affects transferrin receptor trafficking.

Targeting of many transmembrane proteins to post-Golgi compartments is dependent on cytoplasmically exposed sorting signals. The most widely used signals conform to the tyrosine- or the leucine-based motifs. Both types of signals have been implicated in protein localization to the same intracellular compartments, but previous results from both cell-free experiments and studies of transfected cell lines have indicated that the two types of signals interact with separate components of the sorting machinery. We have overexpressed several transmembrane proteins in stably transfected Madin-Darby canine kidney cells using an inducible promoter system. Overexpression of proteins containing tyrosine- or leucine-based sorting signals resulted in reduced internalization of the transferrin receptor, whereas recycling and polarized distribution was not influenced. Our results indicate that proteins with tyrosine- and leucine-based sorting signals can be transported along common saturable pathways.     

Titrating the effects of mitochondrial complex I impairment in the cell physiology.

The mitochondrial oxidative phosphorylation system consists of five multimeric enzymes (complexes I-V). NADH dehydrogenase or complex I (CI) is affected in most of the mitochondrial diseases and in some neurodegenerative disorders. We have studied the physiological consequences of a partial CI inhibition at the cellular level. We used a genetic model (40% CI-inhibited human-ape xenomitochondrial cybrids) and a drug-induced model (0-100% CI-inhibited cells using different concentrations of rotenone). We observed a quantitative correlation between the level of CI impairment and cell respiration, cell growth, free radical production, lipid peroxidation, mitochondrial membrane potential, and apoptosis. We showed that cell death was quantitatively associated with free radical production rather than with a decrease in respiratory chain function. The results obtained with human xenomitochondrial cybrid cells were compatible with those observed in rotenone-induced 40% CI-inhibited cells. At high concentrations (5-6-fold higher than the concentration necessary for 100% CI inhibition), rotenone showed a second toxic effect at the level of microtubule assembly, which also led to apoptosis. The correlation found among all the parameters studied helped clarify the physiological consequences of partial CI inhibitions at the cellular level.     

Introduced plants in the indigenous Pharmacopoeia of Northern South America

The intellectual property rights debate focuses on the flow of germplasm from developing tropical countries to developed temperate nations. Few investigators have addressed the converse. We discuss the abundance and importance of introduced plants in pharmacopoeias of northern South America. Introduced species commonly are employed as medicines throughout the region and include at least 216 Eurasian, North American, African, and Pacific species. Among the Shuar of lowland Ecuador, four introduced plants (Citrus aurantium, Cymbopogon citratus, Saccharum officinarum, and Zingiber officinale) are included in their most commonly prescribed remedies. The widespread use of introduced plants is due, in part, to the medicinal value of plants whose primary use is for food (e.g., Musa X paradisiacal Similarly, many introduced ornamentals also have therapeutic value (e.g., Hedychium coronarium). Other species have been introduced specifically as medicines (e.g., Aloe vera). Restrictions on the flow of germplasm and plant knowledge may protect the economic interests of governments and national industry. If applied bilaterally, however, constraints on the movement of plants will limit the continued evolution of traditional medicinal systems in areas where they are most needed.     

Detailed flow patterns in the nasal cavity.

The human nasal cavity filters and conditions inspired air while providing olfactory function. Detailed experimental study of nasal airflow patterns has been limited because of the complex geometry of the nasal cavity. In this work, particle image velocimetry was used to determine two-dimensional instantaneous velocity vector fields in parallel planes throughout a model of the nasal cavity that was subjected to a nonoscillatory flow rate of 125 ml/s. The model, which was fabricated from 26 computed tomography scans by using rapid prototyping techniques, is a scaled replica of a human right nasal cavity. The resulting vector plots show that the flow is laminar and regions of highest velocity are in the nasal valve and in the inferior airway. The relatively low flow in the olfactory region appears to protect the olfactory bulb from particulate pollutants. Low flows were also observed in the nasal meatuses, whose primary function has been the subject of debate. Comparison of sequentially recorded data suggests a steady flow.     

The twin threshold model: risk-intermediate foraging by rufous hummingbirds, Selasphorus rufus

I developed two versions of the twin threshold model (TTM) to assess risk-sensitive foraging decisions by rufous hummingbirds. The model incorporates energy thresholds for both starvation and reproduction and assesses how three reward distributions with a common mean but different levels of variance interact with these critical thresholds to determine fitness. Fitness, a combination of survival and reproduction, is influenced by both the amount of variance in the distributions and the relative position of the common mean between the thresholds. The model predicts that risk-intermediate foraging is often the optimal policy, and that risk aversion is favoured as the common mean of the distributions approaches the starvation threshold, whereas risk preference is favoured as the common mean approaches the reproduction threshold. Tests with free-living hummingbirds supported these predictions. Hummingbirds were presented with three distributions of nectar rewards that had a common mean but Nil, Moderate or High levels of variance. Birds preferred intermediate levels of variance (Moderate) when presented with all three rewards simultaneously, and became more risk-averse as the mean of the distributions was decreased but more risk-prone as the mean was increased. Birds preferred Nil when it was paired with Moderate or with High, but preferred Moderate in the presence of Nil and High together. This reversal of preference is a violation of regularity, conventionally interpreted as irrational choice behaviour. I provide an alternative version of the TTM demonstrating that violations of regularity can occur when relative instead of absolute evaluation mechanisms are used.     

Lactose repressor protein modified with dansyl chloride: activity effects and fluorescence properties

Chemical modification using 5-(dimethylamino)naphthalene-1-sulfonyl chloride (dansyl chloride) has been used to explore the importance of lysine residues involved in the binding activities of the lactose repressor and to introduce a fluorescent probe into the protein. Dansyl chloride modification of lac repressor resulted in loss of operator DNA binding at low molar ratios of reagent/monomer. Loss of nonspecific DNA binding was observed only at higher molar ratios, while isopropyl beta-D-thiogalactoside binding was not affected at any of the reagent levels studied. Lysine residues were the only modified amino acids detected. Protection of lysines-33 and -37 from modification by the presence of nonspecific DNA correlated with maintenance of operator DNA binding activity, and reaction of lysine-37 paralleled operator binding activity loss. Energy transfer between dansyl incorporated in the core region of the repressor protein and tryptophan-201 was observed, with an approximate distance of 23 A calculated between these two moieties.     

Hemopexin-mediated heme uptake by liver. Characterization of the interaction of heme-hemopexin with isolated rabbit liver plasma membranes

Plasma membranes isolated from rabbit liver retain the ability to interact specifically with heme-hemopexin. In this system, apohemopexin does not compete effectively with heme-hemopexin for binding. The membranes bind heme-hemopexin complexes with high affinity (KD = 6.8 X 10(-7) M) and with an apparent capacity of 2.3 pmol/mg of membrane protein. These membranes also retain the ability to remove heme from heme-hemopexin. The release of heme reaches a plateau after 15-30 min at 30 degrees C and does not involve metabolic energy, proteolysis of hemopexin or pH gradients. The apohemopexin formed is rapidly released from the membranes. The accumulation of heme is saturable and is affected by pH and temperature with maximum uptake occurring between pH 5.5 and 6.5 and at 30 degrees C. Interestingly, much more heme (approximately 25 pmol/mg of membrane protein) is accumulated than hemopexin at saturation, implying that the receptor can turn over several times and that a heme-binding component exists in the rabbit liver plasma membrane.     

Decompression outcome following saturation dives with multiple inert gases in rats

This investigation examined the question of whether gas mixtures containing multiple inert gases provide a decompression advantage over mixtures containing a single inert gas. Unanesthetized male albino rats, Rattus norvegicus, were subjected to 2-h simulated dives at depths ranging from 145 to 220 fsw. At pressure, the rats breathed various He-N2-Ar-O2 mixtures (79.1% inert gas-20.9% O2); they were then decompressed rapidly (within 10 s) to surface pressures. The probability of decompression sickness (DCS), measured either as severe bends symptoms or death, was related to the experimental variables in a Hill equation model incorporating parameters that account for differences in the potencies of the three gases and the weight of the animal. The relative potencies of the three gases, which affect the total dose of decompression stress, were determined as significantly different in the following ascending order of potency: He less than N2 less than Ar; some of these differences were small in magnitude. With mixtures, the degree of decompression stress diminished as either N2 or Ar was replaced by He. No obvious advantage or disadvantage of mixtures over the least potent pure inert gas (He) was evident, although limits to the expectation of possible advantage or disadvantage of mixtures were defined. Also, model analysis did not support the hypothesis that the outcome of decompression with multiple inert gases in rats under these experimental conditions can be explained totally by the volume of gas accumulated in the body during a dive.