Purification and characterization of cytochrome c oxidase from rat liver mitochondria.

Cytochrome c oxidase has been purified from rat liver mitochondria using affinity chromatography. The preparation contains 10.5 to 13.4 nmol of heme a + a3 per mg of protein and migrates as a single band during polyacrylamide gel electrophoresis under nondissociating conditions. It has a heme a/a3 ratio of 1.12 and is free of cytochromes b, c, and c1 as well as the enzymes, NADH dehydrogenase, succinic dehydrogenase, coenzyme Q-cytochrome c reductase, and ATPase. The enzyme preparation consists of six polypeptides having apparent Mr of 66,000, 39,000, 23,000, 14,000, 12,500 and 10,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The peptide composition is similar to those found for cytochrome c oxidases from other systems. The enzymatic activity of the purified enzyme is completely inhibited by carbon monoxide or cyanide, partially inhibited by Triton X-100 and dramatically enhanced by Tween 80 or phospholipids.     

Gas exchange characteristics and nitrogen relations of two Mediterranean root hemiparasites:Bartsia trixago andParentucellia viscosa

Plant height, light-saturated rates of photosynthesis (A _max) and foliar nitrogen concentration (N ₁) were measured forBartsia trixago under field conditions in Mallorca. All three variables were postively correlated, and were also positively related to the abundance of nitrogen-fixing legumes in the associated vegetation (putative host species).A _max forB. trixago ranged from 7.7 to 18.8 mol m^-2 s^-1; similar rates were measured for a second hemiparasiteParentucellia viscosa, and both species were within the range of rates measured for six putative hosts (10.6–19.2 mol m^-2 s^-1). Fertilization of unattachedB. trixago plants with inorganic nitrogen (ammonium nitrate) elicited neither the growth nor the photosynthetic responses observed in plants considered to be parasitic on legumes and in receipt of an enriched organic nitrogen supply. Both hemiparasites had high diurnal leaf conductances (g _s) (469–2291 mmol m^-2 s^-1) and were at the upper end of the range of those measured in putative hosts (409–879 mmol m^-2 s^-1). In contrast with the latter, high nocturnal rates ofg _s were also recorded for the two hemiparasites (517–1862 mmol m^-2 s^-1). There was no clear relationship between eitherA _max orN ₁ and eitherg _s, transpiration (E) or water use efficiency (A _max/E) inB. trixago plants. The economics of water loss appear to be independent of both the supply of nitrogen from the host and autotrophic carbon fixation.     

Impact of emotion on consciousness: positive stimuli enhance conscious reportability

Emotion and reward have been proposed to be closely linked to conscious experience, but empirical data are lacking. The anterior cingulate cortex (ACC) plays a central role in the hedonic dimension of conscious experience; thus potentially a key region in interactions between emotion and consciousness. Here we tested the impact of emotion on conscious experience, and directly investigated the role of the ACC. We used a masked paradigm that measures conscious reportability in terms of subjective confidence and objective accuracy in identifying the briefly presented stimulus in a forced-choice test. By manipulating the emotional valence (positive, neutral, negative) and the presentation time (16 ms, 32 ms, 80 ms) we measured the impact of these variables on conscious and subliminal (i.e. below threshold) processing. First, we tested normal participants using face and word stimuli. Results showed that participants were more confident and accurate when consciously seeing happy versus sad/neutral faces and words. When stimuli were presented subliminally, we found no effect of emotion. To investigate the neural basis of this impact of emotion, we recorded local field potentials (LFPs) directly in the ACC in a chronic pain patient. Behavioural findings were replicated: the patient was more confident and accurate when (consciously) seeing happy versus sad faces, while no effect was seen in subliminal trials. Mirroring behavioural findings, we found significant differences in the LFPs after around 500 ms (lasting 30 ms) in conscious trials between happy and sad faces, while no effect was found in subliminal trials. We thus demonstrate a striking impact of emotion on conscious experience, with positive emotional stimuli enhancing conscious reportability. In line with previous studies, the data indicate a key role of the ACC, but goes beyond earlier work by providing the first direct evidence of interaction between emotion and conscious experience in the human ACC.     

Purification and receptor binding properties of complexes between lutropin and monovalent antibodies against its alpha subunit.

A complex between bovine lutropin (LH) and monovalent antibodies (Fab fragments) directed against its alpha subunit, which is common to the glycoprotein hormones, has been purified by gel filtration and chromatography on concanavalin A-Sepharose. The complex is heterogenous with respect to molecular size; 70--80% of the hormone is complexed with either two or three Fab fragments. The LH-Fab alpha complexes retain only about 13% receptor binding activity as compared to LH when measured in a radioligand receptor assay in which the radiolabeled ligand is human choriogonadotropin. (Use of the human hormone as labeled ligand permits direct measurement of competition between receptor and the bovine complex because the alpha portion of the human hormone does not cross react significantly with antibodies directed against bovine alpha subunits.) Complex formation does not lead to dissociation of the lutropin into its subunits, as shown with a homologous LH-beta immunoassay which distinguishes free beta subunit from intact LH. Complexing of LH with Fab-alpha fragments also causes little or no change in the affinity of the hormone's beta subunit for anti-LH-beta antibodies indicating that significant changes in beta subunit conformation did not occur. The data show that at least two well-separated antigenic regions on the alpha subunit are exposed to the surface in the intact hormone. They are also in agreement with the proposal that the loss of binding activity to receptor is due to steric effects rather than to changes in conformation or dissociation, and that there may be sites on the alpha subunit which interact directly with the receptor.     

An experimental simulation of changes in diatom and flagellate blooms

The sequence of events from a diatom to a flagellate bloom were simulated in a large sea-water enclosure. The two factors used to control the sequence were light and nutrients. The results indicate that diatom growth can be manipulated to occur under specific conditions of light intensity and nutrient concentrations. Once diatom growth has begun it appears to be more rapid than that of the flagellates. The importance of this experiment to the study of food chain Ecology in the sea is discussed.