云南呈贡梁王山现代花粉雨的研究

本文通过对云南呈贡梁王山5块表土分析,初步研究了主要植物花粉的百分含量与其植物覆盖率之间的数量关系,并用校正系数R值表示。按照R值的大小,分为两组:R>1属于超代表性,包括有松、桤木、马桑、蒿和部分蕨类植物;R<1属于低代表性,包括有油杉、栲和石栎、滇青冈、栎、铁仔。在分析松粉分布特征基础上,认为昆明地区西风急流对松粉的传播是主要因素。     

Effects of chloroquine on the torsional dynamics and rigidities of linear and supercoiled DNAs at low ionic strength

The magnitude and uniformity of the torsion elastic constant (alpha) of linear and supercoiled pBR322 DNAs are measured in 3 mM Tris as a function of added chloroquine/basepair ratio (chl/bp) by studying the fluorescence polarization anisotropy of intercalated ethidium dye. The time-resolved FPA is measured using a picosecond dye-laser for excitation and time-correlated single-photon counting detection. For both linear and supercoiled DNAs, alpha remains uniform except at the very highest chl/bp ratio examined. For the linear DNA, alpha decreases from 5.0 x 10(-12) dyne-cm at chl/bp = 0 to about 3.5 x 10(-12) dyne-cm at chl/bp = 0.5, and remains at that value up to chl/bp = 5, whereupon it increases back up to its original value. For the supercoiled DNA, alpha remains constant at about 5.2 x 10(-12) dyne-cm from chl/bp = 0 up to chl/bp = 5, whereupon it increases in parallel with the linear DNA. The effect of chloroquine on the secondary structure, torsion constant, and torsional dynamics evidently differs substantially between linear and supercoiled DNAs, even under conditions where the supercoiled DNA is completely relaxed and both DNAs bind the same amount of dye. This strongly contradicts any notion that the local structures of linear and relaxed supercoiled DNA/dye complexes with the same binding ratio are identical. The increase in apparent alpha at chl/bp = 5 for both DNAs may be due to stacking of the chloroquine in the major groove and consequent stiffening of the filament.     

Physiological Characterization of Dicarboxylate-Induced Pleomorphic Forms of Bradyrhizobium japonicum

When Bradyrhizobium japonicum I-110 was transferred into medium containing 40 mM succinate or 40 mM fumarate, over 90% of the bacteria acquired a swollen, pleomorphic form similar to that of bacteroids. The induction of pleomorphism was dependent on the carbon substrate and concentration but was independent of the hydrogen ion and sodium ion concentration. Cell extracts of rod-shaped and pleomorphic cells contained enzymes required for sugar catabolism and gluconeogenesis. Variations in these enzyme profiles were correlated with the carbon source used and not with the conversion to the bacteroid-like morphology. Rod-shaped cells cultured on glucose or 10 mM succinate transported glucose and succinate; however, the pleomorphic cells behaved similarly to symbiotic bacteroids in that they lacked the ability to transport glucose and transported succinate at lower rates than did rod-shaped cells.     

Growth hormone-induced alteration of morphology and tubulin expression in 3T3 preadipose cells

Effects of growth hormone on morphology and cytoskeletal protein expression were examined in 3T3-F442A preadipocytes in serum-free medium. Between 2 and 5 days of culture 2 nM methionyl human growth hormone converted 3T3-F442A cells from a flat fibroblastic morphology to a rounded form with numerous membrane convolutions. Growth hormone treated cultures manifested a 30-40% reduction in cell volume. Growth hormone induced changes in morphology and volume preceded and were independent of lipogenesis. In cells treated with growth hormone, expression of alpha and beta-tubulin as determined by Western blotting was found to increase approximately 50% within 72 h as compared to untreated cells. After 7 days, tubulin levels in growth hormone treated cells were approximately 40% of control levels. This indicated that morphological changes and alteration of tubulin expression were signatures of growth hormone action on 3T3-F442A cells.     

Comparison of chemical analyses of boat and helicopter-collected water samples

Helicopters can be used to collect water samples from many lakes over a wide geographic area within a relatively short time period. Here we report the results from an experiment in which sequential water samples from a lake were collected first from a nonmotorized boat and then immediately afterward from a helicopter. No significant differences were found between the means of the measurement of 20 chemical parameters for the two methods of collection. When compared to obtaining samples from a boat, collection of samples from a helicopter platform had no effect on the content of the water samples.     

Temperature-dependent insertion of prolipoprotein into Escherichia coli membrane vesicles and requirements for ATP, soluble factors, and functional SecY protein for the overall translocation process.

The requirements for the translocation of prolipoprotein into membrane vesicles were examined in an in vitro system. As measured by the eventual modification and processing of the prolipoprotein to form mature lipoprotein, the overall translocation process was found to require ATP hydrolysis, the presence of some heat-labile soluble cytoplasmic translocation factors, and the function of a cytoplasmic membrane protein, SecY/PrlA. However, the initial step of complete insertion of prolipoprotein into the membrane vesicles occurred without apparent requirements of a nucleotide, cytoplasmic translocation factors, or a functional SecY/PrlA membrane protein. Immunopurified prolipoprotein spontaneously inserted into membrane vesicles at elevated temperatures and required ATP and cytoplasmic translocation factors to form mature lipoprotein. The prolipoprotein inserted most efficiently into liposomes made of negatively charged phospholipids, indicating the importance of phospholipids in protein translocation. These results suggest that ATP hydrolysis and the actions of both cytoplasmic translocation factors and a functional SecY/PrlA membrane protein occur at a step(s) after the insertion of the precursors into membrane vesicles. The initial step of spontaneous insertion of prolipoprotein into membranes is in good agreement with membrane trigger hypothesis proposed by W. Wickner (Annu. Rev. Biochem. 48:23-45, 1979) and the helical hairpin hypothesis proposed by D. M. Engleman and T. A. Steitz (Cell 23:411-422, 1981).     

Opioid-binding protein (OBCAM) is rich in β-sheets

Based on circular dichroism (CD) and the sequence-predictive method, the opioid-binding cell adhesion molecule (OBCAM) consisted of one half -sheets and one fourth -helices. This is consistent with significant sequence homology of the protein to several members of the immunoglobulin (Ig) superfamily, particularly cell adhesion molecules, which are rich in -sheets. Hydropathy analysis suggests that hydrophobic and hydrophilic regions were evenly distributed along the sequence, but the NH₂- and COOH-termini were hydrophobic. Hydrophobic moments and Fourier-transform amphipathic analyses further suggest that residues 23–30 and 83–93 were amphiphathie -sheets. The overall conformation of OBCAM was unaltered by adding linoleic acid, which is required for opioid ligand binding.