室温下有取向紫膜薄层中菌紫质的光静态

在室温条件下有取向PM薄层中的RR分子受光照可以建立多种PSS,这些PSS的建立与湿度和光照所采用的波长等因素有关。不同的PSS有不同的VCD。它们可以在设计制作分子器件时考虑使用。     

Characterization of High-Affinity Dopamine D2 Receptors and Modulation of Affinity States by Guanine Nucleotides in Cholate-Solubilized Bovine Striatal Preparations

3,4-Dihydroxyphenylethylamine (dopamine) D2 receptors, solubilized from bovine striatal membranes using a cholic acid-NaCl combination, exhibited the typical pharmacological characteristics of both agonist and antagonist binding. The rank order potency of the agonists and antagonists to displace [3H]spiroperidol binding was the same as that observed with membrane-bound receptors. Computer-assisted analysis of the [3H]spiroperidol/agonist competition curves revealed the retention of high- and low-affinity states of the D2 receptor in the solubilized preparations and the proportions of receptor subpopulations in the two affinity states were similar to those reported in membrane. Guanine nucleotide almost completely converted the high-affinity sites to low-affinity sites for the agonists. The binding of the high-affinity agonist [3H]N-n-propylnorapomorphine ([3H]NPA) was clearly demonstrated in the solubilized preparations for the first time. Addition of guanylyl-imidodiphosphate completely abolished the [3H]NPA binding. When the solubilized receptors were subjected to diethylaminoethyl-Sephacel chromatography, the dopaminergic binding sites eluted in two distinct peaks, showing six- to sevenfold purification of the receptors in the major peak. Binding studies performed on both peaks indicated that the receptor subpopulation present in the first peak may have a larger proportion of high-affinity binding sites than the second peak. The solubilized preparation also showed high-affinity binding of [35S]guanosine-5'-(gamma-thio)triphosphate, a result suggesting the presence of guanine nucleotide binding sites, which may interact with the solubilized D2 receptors. These data are consistent with the retention of the D2 receptor-guanine nucleotide regulatory protein complex in the solubilized preparations and should provide a suitable model system to study the receptor-effector interactions.     

Transient state characteristics of adaptation to changes in light conditions for the cyanobacterium Oscillatoria agardhii

Transitions in growth irradiance level from 92 to 7 Em^-2 s^-1 and vice versa caused changes in the pigment contents and photosynthesis of Oscillatoria agardhii. The changes in chlorophyll a and C-phycocyanin contents during the transition from high to low irradiance (HL) were reflected in photosynthetic parameters. In the LH transition light utilization efficiencies of the cells changed faster than pigment contents. This appeared to be related to the lowering of light utilization efficiencies of photosynthesis. As a possible explanation it was hypothesized that excess photosynthate production led to feed back inhibition of photosynthesis. Time-scales of changes in the maximal rate of O₂ evolution were discussed as changes in the number of reaction centers of photosystem II in relation to photosynthetic electron transport. Parameters that were subject to change during irradiance transitions obeyed first order kinetics, but hysteresis occurred when comparing HL with LH transients. Interpretation of first order kinetic analysis was discussed in terms of adaptive response vs changes in growth rate.Non-standard abbreviations Chla chlorophyll a - CPC C-phycocyanin - PS II photosystem II - PS I photosystem I - RC II reaction center of photosystem II - P photosynthetic O₂-evolution - I irradiance, Em^-2 s^-1 - light utilization efficiency of cells, mmol O₂·mg dry wt^-1·h^-1/Em^-2 s^-1 - light utilization efficiency of photosynthetic apparatus, mol O₂·mol Chla ^-1·h^-1/Em^-2 s^-1 - P_max maximal rate of O₂ evolution by cells, mol O₂·mg dry wt^-1·h^-1 - P_max maximal rate of O₂ evolution by photosynthetic apparatus, mol O₂·mol·Chla ^-1·h^-1 - LL low light, E m^-2 s^-1 - HL high light, E m^-2 s^-1 - LH low to high light transition - HL high to low light transition - k specific rate of adaptation, h^-1 - specific growth rate, h^-1 - Q pool size of cell constituent, mol·mg dry wt^-1 - q net synthesis rate of cell constituent, mol·mg dry wt^-1·h^-1     

Local denaturation in DNA molecules

A two-dimensional anharmonic model, the so-called Toda-Lennard-Jones model, is considered in order to investigate the problems related to the lifetime of the open states precursors to full denaturation, in inhomogeneous ring-shaped DNA molecules. It is found that a transition from double-stranded to single-stranded DNA occurs locally around physiological temperature. Moreover, the presence of inhomogeneities enhances the hydrogen bond breaking.     

Cellular location,activity states,and macromolecular organization of glucoamylase in Clostridium thermosaccharolyticum

By application of immunocytochemical techniques at the electron microscope level, glucoamylase was localized to the cell periphery in Clostridium thermosaccharolyticum during and following growth on starch, sucrose or glucose. Levels of immunolabelling were found to be relatively independent of growth substrate and of phase of growth, whereas previous studies had demonstrated strong dependence of glucoamylase activity on growth conditions; previously high levels of glucoamylase activity had been detected after growth on starch (i.e. during the stationary phase after growth) and only very low activities detected during exponential growth and following growth on glucose. The results presented demonstrate that levels of the glucoamylase protein are independent of measurable enzyme activity, and imply that the protein is constitutive. This indicates that the protein can exist in active and inactive states in the cell. By analogy with similar systems, we consider it likely that maturation or activation of newly synthesized glucoamylase occurs during (or following) transport through the cytoplasmic membrane. Electron microscopy of individual protein molecules which had been subjected to negative staining revealed that the enzyme consists of two domains of approximately equal size which are linked by a hinge region.     

Molecular modelling of the photoconduction mechanism by charged solitons intrans-polyacetylene: I

It is possible to rationalize the different steps involved in the photoconductivity observed intrans-polyacetylene (t-PA) in terms of a simple chemical model. The interchain electron transfer (IET) and the intrachain polaron capture by neutral solitons proposed by Orensteinat al. may be represented within a simple molecular orbital (MO) picture. An efficiency index for the IET is proposed in terms of the binding energy of the charged polarons and of the electronic chemical potential. The predictive power of the efficiency index is analyzed in the context of the global softness concept. An MO protocol is described to obtain estimates of the IET hopping probabilities.     

Perturbations of the denatured state ensemble: modeling their effects on protein stability and folding kinetics.

By considering the denatured state of a protein as an ensemble of conformations with varying numbers of sequence-specific interactions, the effects on stability, folding kinetics, and aggregation of perturbing these interactions can be predicted from changes in the molecular partition function. From general considerations, the following conclusions are drawn: (1) A perturbation that enhances a native interaction in denatured state conformations always increases the stability of the native state. (2) A perturbation that promotes a non-native interaction in the denatured state always decreases the stability of the native state. (3) A change in the denatured state ensemble can alter the kinetics of aggregation and folding. (4) The loss (or increase) in stability accompanying two mutations, each of which lowers (or raises) the free energy of the denatured state, will be less than the sum of the effects of the single mutations, except in cases where both mutations affect the same set of partially folded conformations. By modeling the denatured state as the ensemble of all non-native conformations of hydrophobic-polar (HP) chains configured on a square lattice, it can be shown that the stabilization obtained from enhancement of native interactions derives in large measure from the avoidance of non-native interactions in the D state. In addition, the kinetic effects of fixing single native contacts in the denatured state or imposing linear gradients in the HH contact probabilities are found, for some sequences, to significantly enhance the efficiency of folding by a simple hydrophobic zippering algorithm. Again, the dominant mechanism appears to be avoidance of non-native interactions. These results suggest stabilization of native interactions and imposition of gradients in the stability of local structure are two plausible mechanisms involving the denatured state that could play a role in the evolution of protein folding and stability.