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81.
Light has a profound influence on ochratoxin biosynthesis by Penicillia. When incubated under constant daylight of a certain
intensity, ochratoxin A biosynthesis is decreased by about 20–30% compared to incubation under constant darkness. Under day/night
oscillation, the ochratoxin A polyketide synthase gene, a key gene of the ochratoxin A biosynthesis pathway, is rhythmically
expressed, and moreover, the amount of ochratoxin also oscillates between the amounts produced either during constant darkness
or during constant light. This indicates a partial degradation of ochratoxin A (20–30%) under light conditions until a certain
lower limit is reached. This behavior is dependent on the light intensity. At 1,600 Lux, only weak effects could be observed;
however, at 2,800 Lux, the effects became significant. After growth under constant light conditions, Penicillium produced ochratoxin B at amounts which are 5 times higher than after growth in constant dark or in alternating light/dark
conditions. Growth experiments in the dark on medium with increasing amounts of ochratoxin A revealed that externally applied
ochratoxin is moderately toxic. However, if the same growth experiments are carried out under light conditions, the growth
inhibiting activity of ochratoxin A is greatly increased, indicating that light amplifies the toxic activity of ochratoxin.
Because of the oscillation of the concentration of ochratoxin A during night and day incubation, Penicillium seems to have developed an adaptive mechanism to reduce the amount of ochratoxin A during daylight below a toxic level. 相似文献
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Legall H Stiel H Beck M Leupold D Gruszecki WI Lokstein H 《Journal of biochemical and biophysical methods》2007,70(3):369-376
Peridinin-chlorophyll a protein (PCP) is a unique water soluble antenna complex that employs the carotenoid peridinin as the main light-harvesting pigment. In the present study the near edge X-ray absorption fine structure (NEXAFS) spectrum of PCP was recorded at the carbon K-edge. Additionally, the NEXAFS spectra of the constituent pigments, chlorophyll a and peridinin, were measured. The energies of the lowest unoccupied molecular levels of these pigments appearing in the carbon NEXAFS spectrum were resolved. Individual contributions of the pigments and the protein to the measured NEXAFS spectrum of PCP were determined using a “building block” approach combining NEXAFS spectra of the pigments and the amino acids constituting the PCP apoprotein. The results suggest that absorption changes of the pigments in the carbon near K-edge region can be resolved following excitation using a suitable visible pump laser pulse. Consequently, it may be possible to study excitation energy transfer processes involving “optically dark” states of carotenoids in pigment-protein complexes by soft X-ray probe optical pump double resonance spectroscopy (XODR). 相似文献
87.
The anatomy and the physiology of the prosternal chordotonal organ (pCO) within the prothorax of Sarcophaga bullata is analysed. Neuroanatomical studies illustrate that the approximately 35 sensory axons terminate within the median ventral association centre of the different neuromeres of the thoracico-abdominal ganglion. At the single-cell level two classes of receptor cells can be discriminated physiologically and morphologically: receptor cells with dorso-lateral branches in the mesothoracic neuromere are insensitive to frequencies below approximately 1 kHz. Receptor cells without such branches respond most sensitive at lower frequencies. Absolute thresholds vary between 0.2 and 8m/s(2) for different frequencies. The sensory information is transmitted to the brain via ascending interneurons. Functional analyses reveal a mechanical transmission of forced head rotations and of foreleg vibrations to the attachment site of the pCO. In summed action potential recordings a physiological correlate was found to stimuli with parameters of leg vibrations, rather than to those of head rotation. The data represent a first physiological study of a putative predecessor organ of an insect ear. 相似文献
88.
Kuhlmann CR Tamaki R Gamerdinger M Lessmann V Behl C Kempski OS Luhmann HJ 《Journal of neurochemistry》2007,102(2):501-507
Increased mortality after stroke is associated with development of brain edema. The aim of the present study was to examine the contribution of endothelial myosin light chain (MLC) phosphorylation to hypoxia-induced blood-brain barrier (BBB) opening. Measurements of trans-endothelial electrical resistance (TEER) were performed to analyse BBB integrity in an in vitro co-culture model (bovine brain microvascular endothelial cells (BEC) and rat astrocytes). Brain fluid content was analysed in rats after stroke induction using a two-vein occlusion model. Dihydroethidium was used to monitor intracellular generation of reactive oxygen species (ROS) in BEC. MLC phosphorylation was detected using immunohistochemistry and immunoblot analysis. Hypoxia caused a decrease of TEER values by more than 40%, which was prevented by inhibition of the MLC-kinase (ML-7, 10 micromol/L). In addition, ML-7 significantly reduced the brain fluid content in vivo after stroke. The NAD(P)H-oxidase inhibitor apocynin (500 micromol/L) prevented the hypoxia-induced TEER decrease. Hypoxia-dependent ROS generation was completely abolished by apocynin. Furthermore, ML-7 and apocynin blocked hypoxia-dependent phosphorylation of MLC. Our data demonstrate that hypoxia causes a breakdown of the BBB in vitro and in vivo involving ROS and the contractile machinery. 相似文献
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Expression of selenocysteine (Sec)-containing proteins requires the presence of a cis-acting mRNA structure, called selenocysteine insertion sequence (SECIS) element. In bacteria, this structure is located in the coding region immediately downstream of the Sec-encoding UGA codon, whereas in eukaryotes a completely different SECIS element has evolved in the 3'-untranslated region. Here, we report that SECIS elements in the coding regions of selenoprotein mRNAs support Sec insertion in higher eukaryotes. Comprehensive computational analysis of all available viral genomes revealed a SECIS element within the ORF of a naturally occurring selenoprotein homolog of glutathione peroxidase 4 in fowlpox virus. The fowlpox SECIS element supported Sec insertion when expressed in mammalian cells as part of the coding region of viral or mammalian selenoproteins. In addition, readthrough at UGA was observed when the viral SECIS element was located upstream of the Sec codon. We also demonstrate successful de novo design of a functional SECIS element in the coding region of a mammalian selenoprotein. Our data provide evidence that the location of the SECIS element in the untranslated region is not a functional necessity but rather is an evolutionary adaptation to enable a more efficient synthesis of selenoproteins. 相似文献