裸子植物的盛世--评价"《Heyday of the Gymnosperms:Systematics and Biodiversity of the Late Triassic Molteno Formation》.John M.Anderson and Heidi M.Anderson,2003.Strelitzia,15,1-398pp.National Botanical Institute,Pretoria,South Africa"

近日南非比勒陀利亚国家植物研究所约翰·安特生和海迪·安特生博士寄赠他们多年辛勤研究的成果,专著<裸子植物的盛世:晚三叠世摩尔丹诺组繁殖器官的系统分类和生物学多样性>一本并嘱为其写一个评述.自1967年伊始,约翰·安特生博士等就开始专心致力于南非晚三叠世摩尔丹诺组(Molteno Formation)植物化石的研究. 这是他们迄今为止完成的第三部有关的专著.     

M?ssbauer investigations of high-spin ferrous heme proteins. II. Chloroperoxidase, horseradish peroxidase, and hemoglobin.

Reduced samples of chloroperoxidase, horseradish peroxidase, and deoxyhemoglobin were studied by M?ssbauer spectroscopy in strong magnetic fields. The intricate paramagnetic spectra of chloroperoxidase were evaluated in detail in the framework of a spin Hamiltonian pertinent to high-spin ferrous iron. The studies strongly suggest that, in their reduced states, chloroperoxidase from Caldariomyces fumago and cytochrome P-450 from Pseudomonas putida have similar, if not identical ligand structures of the heme iron. The spectral similarities of these two proteins, noted in an earlier M?ssbauer investigation, are further explored and substantiated. Reduced horseradish peroxidase and deoxyhemoglobin, on the other hand, show high-field M?ssbauer spectra that differ considerably from each other and, in particular, from those of the P-450 type, suggesting a different ligand arrangement of the heme iron for each case.     

Production, Characterization, and Properties of β-Glucosidase and β-Xylosidase from a Strain of Aureobasidium sp.

-Glucosidase and -xylosidase production by a yeastlike Aureobasidium sp. was carried out during solid-state and submerged fermentation using different carbon sources and crude enzymes were characterized. -Glucosidase and -xylosidase exhibited optimum activities at pH 2.0–2.5 and 3.0, respectively. These enzymes had the maximum activities at 65°C and were stable in a wide pH range and at high temperatures.     

Structural fluctuations of myoglobin from normal-modes,M?ssbauer,Raman, and absorption spectroscopy.

A normal-mode analysis of carbon monoxymyoglobin (MbCO) and deoxymyoglobin (Mb) with 170 water molecules is performed for (54)Fe and (57)Fe. A projection is defined that extracts iron out-of-plane vibrational modes and is used to calculate spectra that can be compared with those from resonance Raman scattering. The calculated spectra and the isotopic shift (57)Fe versus (54)Fe agree with the experimental data. At low temperatures the average mean square fluctuations (MSFs) of the protein backbone atoms agree with molecular dynamics simulation. Below 180 K the MSFs of the heme iron agree with the data from Mossbauer spectroscopy. The MSFs of the iron atom relative to the heme are an order of magnitude smaller than the total MSFs of the iron atom. They agree with the data from optical absorption spectroscopy. Thus the MSFs of the iron atom as measured by Mossbauer spectroscopy can be used to probe the overall motion of the heme within the protein matrix, whereas the Gaussian thermal line broadening of the Soret band and the resonance Raman bands can be used to detect local intramolecular iron-porphyrin motions.     

Kinetics and mechanism of G-quadruplex formation and conformational switch in a G-quadruplex of PS2.M induced by Pb²⁺

DNA sequences with guanine repeats can form G-quartets that adopt G-quadruplex structures in the presence of specific metal ions. Using circular dichroism (CD) and ultraviolet-visible (UV-Vis) spectroscopy, we determined the spectral characteristics and the overall conformation of a G-quadruplex of PS2.M with an oligonucleotide sequence, d(GTG(3)TAG(3)CG(3)TTG(2)). UV-melting curves demonstrate that the Pb(2+)-induced G-quadruplex formed unimolecularly and the highest melting temperature (T(m)) is 72°C. The analysis of the UV titration results reveals that the binding stoichiometry of Pb(2+) ions to PS2.M is two, suggesting that the Pb(2+) ions coordinate between adjacent G-quartets. Binding of ions to G-rich DNA is a complex multiple-pathway process, which is strongly affected by the type of the cations. Kinetic studies suggest that the Pb(2+)-induced folding of PS2.M to G-quadruplex probably proceeds through a three-step pathway involving two intermediates. Structural transition occurs after adding Pb(NO(3))(2) to the Na(+)- or K(+)-induced G-quadruplexes, which may be attributed to the replacement of Na(+) or K(+) by Pb(2+) ions and the generation of a more compact Pb(2+)-PS2.M structure. Comparison of the relaxation times shows that the Na(+)→Pb(2+) exchange is more facile than the K(+)→Pb(2+) exchange process, and the mechanisms for these processes are proposed.