Pathways of energy flow through the light-harvesting antenna of the photosynthetic purple bacterium rhodobacter sphaeroides

Using low intensity picosecond absorption spectroscopy with independently tunable excitation and probing infrared pulses, we have studied the pathways of energy transport through the light-harvesting antenna pigments of the photosynthetic purple bacterium Rhodobacter sphaeroides. From the observed excited-state rise time of the red-most pigment B896 as a function of excitation wavelength it is concluded that the B850 pigment of LH2 is spectrally heterogeneous. For excitations originating in the B850 pigment this results in a fast channel (9 ps) that is mainly excited in the peak of the B850 absorption band, and a slow channel (35 ps) that is predominantly excited at ~840 nm. Upon excitation of B800, more than 90% of the excitations follow the fast path. From the observed kinetics it is concluded that the majority of the LH2 → LH1 energy transfer takes place within at most a few picoseconds. The rate-limiting step in the whole energy transfer sequence appears to be the B896 → reaction center transfer. The origin of the B850 heterogeneity and the slow 35-ps component is at the moment unclear. Possibly it represents a highly extended form of LH2 in which transfer to LH1 takes a relatively long time, due to a large number of transfer steps.     

鄂尔多斯盆地晚石炭世孢粉组合

本文报道了鄂尔多斯盆地晚石炭世太原组的孢粉组合,共计68属,148种(类型)。本文描述了其中的9个新种,2个新组合和4个未定种,并建立一个组合带,即 Pseudolyosporaradialis-Gulisporites discersus-Thymospora thiessenit。根据孢粉组合情况,可看出盆地东部更接近于华北,西部则发生区系上的变化。整个孢粉组合可与盆地北缘、华北地区的太原组以及欧美等地区的维斯法期 C-D 和斯蒂芬期的孢粉组合比较。地质时代当属晚石炭世。     

Structural basis of the Cks1-dependent recognition of p27(Kip1) by the SCF(Skp2) ubiquitin ligase

The ubiquitin-mediated proteolysis of the Cdk2 inhibitor p27(Kip1) plays a central role in cell cycle progression, and enhanced degradation of p27(Kip1) is associated with many common cancers. Proteolysis of p27(Kip1) is triggered by Thr187 phosphorylation, which leads to the binding of the SCF(Skp2) (Skp1-Cul1-Rbx1-Skp2) ubiquitin ligase complex. Unlike other known SCF substrates, p27(Kip1) ubiquitination also requires the accessory protein Cks1. The crystal structure of the Skp1-Skp2-Cks1 complex bound to a p27(Kip1) phosphopeptide shows that Cks1 binds to the leucine-rich repeat (LRR) domain and C-terminal tail of Skp2, whereas p27(Kip1) binds to both Cks1 and Skp2. The phosphorylated Thr187 side chain of p27(Kip1) is recognized by a Cks1 phosphate binding site, whereas the side chain of an invariant Glu185 inserts into the interface between Skp2 and Cks1, interacting with both. The structure and biochemical data support the proposed model that Cdk2-cyclin A contributes to the recruitment of p27(Kip1) to the SCF(Skp2)-Cks1 complex.     

Characterization of conformational epitope of alginate-derived polymannuronates by surface plasmon resonance

In the present study, we developed a mAb to alginate-derived polymannuronates (ADPM) and examined the antigenic epitopes using surface plasmon resonance (SPR) in conjunction with a large panel of oligomannuronate probes. We found that tetrasaccharide is the minimum-binding unit, and that increases in chain length from the tetrasaccharide to the heptsaccharide further enhance monovalent binding. A sharp increase in affinity was observed when increasing from the octasaccharide to the cosasaccharide, which is due to a further enhancement of the individual antigenic epitope combined with multivalency. Kinetic binding studies further suggested that the conformational epitope is discontinuous and infrequent and that a C6-carboxyl group is important in maintaining the conformational epitope. Moreover, CD analysis revealed there were conformational structures in epitopes. The data support our hypothesis that the conformational epitope for the mAb may be an extended helical segment of ADPM. ADPM exists mainly in linear form, but it can infrequently and spontaneously form extended helices. Although helices are not prevalent in ADPM, the immune system preferentially selects these conformational epitopes because they are unique. Together, our results indicate that the antigenic epitopes in beta-d-mannuronates are conformational and require C6-carboxyl groups.     

Theoretical approach to blood ejection from the human left ventricle

An ejection dynamics mathematical model of human left ventricle (LV) based on physiological data of human heart is proposed in this study. The mathematical equations were expressed in terms of vorticity-stream function equations in a prolate spheroidal coordinate system. These equations combined with specified boundary conditions were numerically solved by using an alternating-direction-implicit (ADI) algorithm with second order accuracy. The unsteady aspects of the ejection process were subsequently introduced into the numerical simulation. The numerical results have shown that the present ellipsoidal model could be available to simulate the ejection process of the human LV. Such a model combined with cardiac muscle mechanics could be studied further to determine altered left ventricular function in cardiac diseases.     

Dysfunction of myocardial sarcoplasmic reticulum in rats with myocardial calcification

We investigated the relationship between cardiac dysfunction and Ca2+ transport in the myocardial sarcoplasmic reticulum (SR) during the pathogenesis of cardiovascular calcification in rats. The possible mechanism of SR dysfunction was explored by detecting the alteration of the nitric oxide/nitric oxide synthase (NO/NOS) pathway in the SR. Using the vitamin D plus nicotine (VDN treatment for 2 week and 6 week) experimental model of cardiac calcification, cardiac function and sarcoplasmic reticulum function were measured. Inhibition of cardiac functions in vivo (peak rate of contraction and peak rate of relaxation, P < 0.05 or P < 0.01) were observed in all calcification groups, simultaneously, Ca2+ release and uptake in the SR as well as the Ca2+ release channel and Ca2+ pump activity were inhibited. Myocardial Ca2+ concentration and cardiac and SR dysfunction were inversely related (P < 0.05). The specific NO/NOS pathway (NO production, NOS activity and nNOS expression in the SR) was upregulated in the SR and associated with calcification (both 2- and 6 week VDN groups). These results indicate that cardiac dysfunction associated with myocardial calcification might be mediated by SR dysfunction, which may result from an impaired SR-specific NO/NOS pathway.     

Morphology and affinities of an Early Cretaceous Ephedra (Ephedraceae) from China

Detailed investigations on Lower Cretaceous Ephedra L. fossils (Gnetopsida) reveal morphological characters similar to those of extant Ephedra rhytidosperma Pachomova, including articulate branches with many fine longitudinal striations, a dichasial branching pattern, uni- or bi-ovulate cones with paired bracts, cones terminal on branchlets, and seeds with a short, straight micropylar tubes, covered by numerous regular and prominent transverse laminar protuberances. Fossils are similar to extant E. rhytidosperma reproductive organs but differ in some vegetative structures and are described and discussed here as Ephedra archaeorhytidosperma Y. Yang et al. Because E. rhytidosperma is currently considered one of the most specialized members in Ephedra L. section Pseudobaccatae Stapf, the occurrence of E. archaeorhytidosperma in the Yixian Formation suggests that Ephedra L. was perhaps a more diverse genus in the Lower Cretaceous. Perhaps the evolution and diversity of Ephedra L. was already in place by the Lower Cretaceous and certainly before the end of the Mesozoic.