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To understand how the protein achieves fluorescence, the isomerization mechanism of the HcRed chromophore is studied both under vacuum and in the solvated red fluorescent protein. Quantum mechanical (QM) and quantum mechanical/molecular mechanical (QM/MM) methods are applied both for the ground and the first excited state. The photoinduced processes in the chromophore mainly involve torsions around the imidazolinone-bridge bond (τ) and the phenoxy-bridge bond (φ). Under vacuum, the isomerization of the cis-trans chromophore essentially proceeds by τ twisting, while the radiationless decay requires φ torsion. By contrast, the isomerization of the cis-trans chromophore in HcRed occurs via simultaneous τ and φ twisting. The protein environment significantly reduces the barrier of this hula twist motion compared with vacuum. The excited-state isomerization barrier via the φ rotation of the cis-coplanar conformer in HcRed is computed to be significantly higher than that of the trans-non-coplanar conformer. This is consistent with the experimental observation that the cis-coplanar-conformation of the chromophore is related to the fluorescent properties of HcRed, while the trans-non-planar conformation is weakly fluorescent or non-fluorescent. Our study shows how the protein modifies the isomerization mechanism, notably by interactions involving the nearby residue Ile197, which keeps the chromophore coplanar and blocks the twisting motion that leads to photoinduced radiationless decay.

The light-driven pump Halorhodopsin (hR) uses the energy stored in an initial meta-stable state (K), in which the bound retinal chromophore has been photoisomerized from all-trans to 13-cis, to drive the translocation of one chloride anion across the membrane. Thus far it was unclear whether retinal twisting or charge separation between the positive Schiff base of the retinal and the chloride anion is the primary mechanism of energy storage. Here, combined quantum mechanical/molecular mechanical (QM/MM) simulations show that the energy is predominantly stored by charge separation. However, a large variability in retinal twisting is observed, thus reconciling the contradictory hypotheses for storage. Surprisingly, the energy stored in the K-state amounts to only one-fifth of the photon energy. We explain why the protein cannot store more: even though this would accelerate chloride pumping, raising the K-state also reduces the relative energy barriers against unproductive decay, in particular via the premature cis to trans back-isomerization. Indeed, the protein has maximized its storage so that the back-isomerization barriers are just high enough (> or =18 kcal/mol) to keep the decay rate (1/100 ms) slower than the remaining photocycle (1/20 ms). This need to stabilize the captured photon-energy until it can be used in subsequent steps is inherent to light-driven proteins.

Chorioamnionitis, as the most frequent cause of second trimester abortions, is commonly diagnosed by histomorphological examination of placental tissue. We determined whether chorioamnionitis induces a fetal extramedullary hematopoietic response and estimated whether chorioamnionitis can be diagnosed from fetal liver alone. Clinical data and morphological and histological findings of 39 second trimester abortions, caused by chorioamnionitis, were compared with 32 age-matched control cases. Using hematoxylin and eosin staining, naphtol-ASD-chloracetate esterase and "Berliner Blau" reaction, total hematopoiesis, erythropoiesis, myelopoiesis and intracytoplasmatic iron of fetal liver were examined. In the study group, total hematopoiesis was increased compared with the controls (94.9% versus 84.4%). The same was seen in erythropoiesis (69.2% versus 56.2%, P>0.05). Chorioamnionitis resulted in a significant increase of fetal myelopoiesis with clustering of leukocytes in 56.4% (P=0.001). Neutrophiles were located predominantly intrasinusoidal and periportal (74.4%), while an isolated periportal location was often observed in controls (50.0%). Isolated perivenous iron storing was more often seen with chorioamnionitis (28.3% versus 3.1%) and correlated with the increasing severity of chorioamnionitis. It can be stated that infectious diseases, such as chorioamnionitis, increase fetal intrahepatic myelopoiesis as one defense mechanism. The morphology of fetal intrahepatic hematopoiesis and iron storing might also be helpful in the diagnosis of chorioamnionitis, especially when the placenta is not available for examination.

Investigations into optimal culture conditions for Bacillus cereus in order to detect bacterial toxins in a cell culture system showed that Dulbecco's modified Eagle's medium supplemented with 5% fetal calf serum is the medium best suited for this purpose. The highest toxicity levels were seen when bacteria were cultured at 21 degrees C. In 42 of 43 Bacillus cereus-strains isolated from milk and milk products, toxin formation was detected using the MTT-test. In 11 strains, toxin formation was even shown when bacteria were cultured at 4 degrees C. When culture supernatants were examined in a commercially available ELISA, all cytotoxic strains were shown to form diarrheal toxin.