Comets and the formation of biochemical compounds on the primitive Earth – A review

Thirty years ago it was suggested that comets impacting on the primitive Earth may have represented a significant source of terrestrial volatiles, including some important precursors for prebiotic synthesis (Oró, 1961,Nature 190: 389). This possibility is strongly supported not only by models of the collisional history of the early Earth, but also by astronomical evidence that suggests that frequent collisions of comet-like bodies from the circumstellar disk around the star Pictoris are taking place. Although a significant fraction of the complex organic compounds that appear to be present in cometary nuclei were probably destroyed during impact, it is argued that cometary collisions with the primitive Earth represented an important source of both free-energy and volatiles, and may have created transient, gaseous environments in which prebiotic synthesis may have taken place.     

Effect of electrical fields and external ionic currents on pollen-tube orientation

Summary Agapanthus umbelatus pollen tubes (PTs) display a number of different growth patterns when germinated in an electric field of 750 mV· mm^–1. When pollen is germinated near the cathode (82.44% of orientation to the cathode side) or near the anode (55.35% of orientation to the anode), growth is oriented parallel to the applied field but when germinated at an intermediate position, there is random growth. An increase and decrease in the orientation rates as well as reversion of the polarized growth were observed when the growth conditions were systematically altered. These findings reflect the influence of different ionic currents present in the germination medium. These ionic currents induce the formation of ionic gradients, which were monitored by ion-HPLC. The individual omission of Ca²⁺, K⁺, Mg²⁺ and Cl^– suppresses or alters the oriented growth pattern. The presence of ionic gradients is not by itself suficient to trigger the polarization of tube growth as the presence of an electric field which drives the ionic currents is essential for this to occur.Abbreviations PT Pollen tube - DNS 3,5-dinitro salycilic acid; - TP transient polarization - HPLC high precision liquid chroma tography - DC direct current     

The amnesic shellfish poison domoic acid enhances neurotoxicity by excitatory amino acids in cultured neurons

Summary A recent episode of human intoxication by cultured mussels containing a rare excitatory amino acid named domoic acid, received particular attention for its neurological implications. The intoxication produced neurological problems, such as headache, confusion, and loss of memory, particularly severe at times. Neuronal damage was found in the hippocampus and amygdala of four patients. We now report that in neuronal cultures the neurotoxicity of a domoic acid-containing mussel extract is the result of domoic acid potentiation of the excitotoxic effect of glutamic acid and aspartic acid present in high amounts in mussel tissue. Moreover, we show that subtoxic concentrations of domoic acid are sufficient to potentiate glutamic acid and aspartic acid neurotoxicity. We present evidence suggesting that the neurotoxic synergism may be due to a reduction of Mg^{+ +} block at the NMDA receptor-associated channel, following activation of NON-NMDA receptors by domoic acid.     

Lipid accumulation inRhodotorula glutinis on sugar cane molasses in single-stage continuous culture

Microbial lipids produced byRhodotorula glutinis grown in continuous culture with molasses under nitrogen-limiting conditions were evaluated and the effects of growth rate on fatty acid composition were studied. As the growth rate decreased, cell biomass, lipid content and lipid yield gradually increased. The maximum lipid content recorded was 39% (w/w) of dry cell biomass at a dilution rate of 0.04 h^–1. The growth rate also affected fatty acid composition: oleic acid decreased with decreasing growth rate while stearic acid increased.     

Risk of prostate,ovarian, and endometrial cancer among relatives of women with breast cancer.

OBJECTIVE--To investigate the risk of prostate, ovarian, and endometrial cancer among relatives of patients with breast cancer. DESIGN--Cohort study of 947 pedigrees in which the proband had breast cancer, linked with the Icelandic cancer registry. SETTING--Iceland. SUBJECTS--The 947 pedigrees included 29,725 people, of whom 1539 had breast cancer, 467 had prostate cancer, 135 ovarian cancer, and 105 endometrial cancer. MAIN OUTCOME MEASURES--Risk of prostate, ovarian, and endometrial cancer among blood relatives of women with breast cancer compared with risk in spouses. RESULTS--The risk of prostate cancer was significantly raised for all relatives (1.5), first degree relatives (1.4), and second degree relatives (1.3) of women with breast cancer. Risk of ovarian cancer was raised for all relatives (1.9) and first degree relatives (1.9) and risk of endometrial cancer was raised for all relatives only (1.9). The risk of prostate cancer was raised if the proband with breast cancer had a first degree relative with prostate cancer. CONCLUSIONS--Coaggregation exists between breast cancer and cancers of the prostate, ovaries, and endometrium. This risk relation is probably based on genes which act by increasing the risk for cancer at these sites. Environmental factors that are common among relatives may also play a part. Continued research is required into pathophysiological mechanisms that could explain these observations.     

pH control of limonin debittering with entrapped Rhodococcus fascians cells

Summary Rhodococcus fascians cells were immobilized by entrapment in -carrageenan. The ability of the system to continuously degrade limonin was tested against pH. A burst of activity was observed when changing from pH 4.5 to 5.0, and a small increase could be seen above the latter value. Such behaviour was not only a response of the metabolic activity of the cells to changes in the medium pH, but to selectivity towards the chemical form of the limonin substrate, which also depends on pH. Additionally, the immobilized cells showed increased resistance against pH changes, since the system recovered almost full activity when the pH was restored to 7.0 after being operated for long periods at pH 4.0. The decrease in limonin-degrading capability of the immobilized cells at low pH values could be overcome by choosing an appropriate dilution rate.Offprint requests to: J. L. Iborra     

Cultural characteristics and zearalenone production by strains of<Emphasis Type="Underline">Fusarium</Emphasis> from wheat

Conidia of the speciesFusarium culmorum /W.G.Sm./ Sacc. andFusarium graminearum Schwabe are characterized by variability in zearalenone production and dimensions depending on the substrate. The sporulation of isolates from some wheat eultivars have been deprived in vivo and in vitro in the first passage, but not their pathogenicity and toxic metabolites production. Nonsporulating strains produced lower quantités of zearalenone than sporulating ones. Liquid filtrates of such nonsporulating strains had a high phytotoxic effect on wheat caryopses. The crystalline toxin DAS /0,25 ug/ml/ had low phytotoxic effect on wheat caryopses.     

A possible pathomechanism of the idiopathic cold contact urticaria.

Urtica is characterized by an erythematous wheal surrounded by a flare and is frequently caused by physical agents (e.g. cold). The exact mechanism and mediators involved in the mechanism of physical urticaria are not known. This study of the role of the neurogenic factors in cold urticaria showed, that local capsaicin treatment (desensitization) of the skin in patients with cold urticaria resulted in the abolition of whealing in response to cold. This result suggests that C-fibers might play an important role in the pathomechanism of idiopathic contact cold urticaria.     

Conditions for recognition of a physical space as two compartments by the paradise fish (Macropodus opercularis, Pisces, Anabantidae).

By using a series of aquaria which were more or less separated into two compartments by a "gate" made of plastic or glass strips, we studied how paradise fish changed their patterns of movement relative to the nature of the gates. We found that opaque plastic gates were well recognized by the paradise fish (Macropodus opercularis) even if the strips were very thin, but that they only changed their pattern of movement when the strips exceeded a certain width. Thus, paradise fish appear to be able to distinguish a physical space of the same size as consisting of either one or two compartments, depending on the material (transparency) and width of the dividing strips.     

The degradative fate of ubiquitin-protein conjugates in nucleated and enucleated cells.

Covalent ligation of multiple copies of ubiquitin to proteins is known to target intracellular proteins for degradation by large molecular weight cytosolic proteinase(s). Ubiquitin protein conjugates are found in cytosolic cell compartments suggesting that ubiquitination may have multiple roles. We have detected ubiquitinated proteins in the lysosomal apparatus of normal fibroblasts and fibroblasts treated with lysosomal proteinase inhibitors. In contrast rabbit reticulocytes lack lysosomes. We present here direct evidence for ubiquitination of mitochondrial proteins during rabbit reticulocyte maturation. In addition ubiquitination appears to be associated with the terminal differentiation of human keratinocytes. These results suggest that: 1. ubiquitin-protein conjugates may be degraded lysosomally 2. organellar proteins may be degraded by the ubiquitin system 3. ubiquitination is involved in the programmed elimination of proteins and organelles from several cell types during differentiation.