胆红素对人胎盘谷胱甘肽S-转移酶的别构效应

胆红素是人胎盘谷胱甘肽S—转移酶(GST—π)的别构效应剂,在胆红素存在下,底物谷胱甘肽(GSH)呈同促正协同效应:胆红素浓度愈高,Hill氏系数(n_H)也愈大,胆红素本身对酶的结合也呈同促正协同效应。胆红素还能加速GST-π在缺乏疏基保护剂时的自然失活,加速GST-π的氨基被2,4,6—三硝基苯磺酸(TNBS)、胍基被丁二酮以及羧基被N-乙基-N’-(3-二甲胺基丙基)羧二亚胺(EDC)的修饰,但却抑制N-乙基顺丁二酰亚胺(NEMI)对疏基的修饰,胆红素这种对失活作用的影响可能和胆红素引起GST-π空间构象的变化有关,对其他可能性也作了讨论。     

玉米花粉单倍体植株染色体上异染色质的变异

我们用Giemsa BSG C-带技术检查了玉米花药培养获得的花粉单倍体植株根尖细胞染色体上异染色质的变异,观察结果表明,有的植株所显示的C-带数目是与供体植株的相一致,有的植株所显示的C-带数目则发生了显著变化,其中有的增加,有的减少。并讨论了异染色质发生变异的可能原因。还相应地观察到间期核中染色中心的变化是与中期染色体上C-带数目的变化相一致。     

叶龄及树冠不同部位光强对黄花梨光合速率的影响

笔者以黄花梨为试材,研究了叶龄及树冠不同部位光强对其光合速率的影响。结果表明:黄花梨叶片在展叶后约11天即有少量光合产物输出,25天时,单叶净光合速率接近最大值;密植梨树高光合叶幕厚度约125cm左右。     

IL-4 blocks the up-regulation of IL-2 receptors induced by IL-2 in normal human B cells

A negative influence of IL-4 on the IL-2-induced B cell proliferation and differentiation has recently been reported. In this study, we have further investigated a role of IL-4 on human tonsillar B cell proliferation and IL-2R expression. IL-4 enhanced Staphylococcus aureus Cowan 1 strain (SAC)-induced B cell proliferation, reaching the peak on day 3. However, from day 4, IL-4 inhibited IL-2-induced proliferation. In the cross-linking study, IL-4 enhanced the density of 125I-IL-2-binding protein at low affinity binding condition (2 nM of 125I-IL-2) in SAC-activated B cells. However, IL-4 blocked the enhancement in the density of 125I-IL-2-binding proteins induced by IL-2, from day 3, in both high (50 pM of 125I-IL-2) and low affinity binding conditions, suggesting that IL-4 is able to block IL-2-induced IL-2R up-regulation. This was confirmed by a binding study: B cells that cultured for 3 days with SAC plus IL-2 expressed an average of 180 +/- 20 high affinity receptors/cell with a Kd of 12 pM and 5800 +/- 500 low affinity receptors/cell with a Kd of 980 pM. By coculturing with IL-4, high affinity receptors were almost undetectable and the expression of low affinity receptors was reduced by more than 80%. IL-4-mediated inhibition of IL-2-induced IL-2R expression does not seem to be due to the direct interaction between IL-4 and cell surface receptors, inasmuch as preincubation of cells with IL-4 for 60 min at 37 degrees C did not alter the binding of 125I-IL-2 to cells previously cultured for 3 days with SAC plus IL-2. These data suggest that IL-4 has a capacity to block the up-regulation of the high as well as low affinity IL-2R-induced by IL-2 in normal human B cells, and could provide a possible explanation for the decreased responsiveness of B cells to IL-2 in the presence of IL-4.     

纽氏钝绥螨、尼氏钝绥螨及其猎物—桔全爪螨生态学特性的比较研究

本文从天敌与猎物的种群内禀增长力,天敌对猎物不同密度的功能反应及数值反应三个方面来评价和比较纽氏钝绥螨、尼氏钝绥螨时其猎物——枯全爪螨的控制作用。在五种温度下,两种捕食螨的种群内禀增长力都大于桔全爪螨。它们对猎物的功能反应属HollingⅡ型。尼氏钝绥螨的捕食量大于纽氏钝绥螨,在25℃时两种捕食螨捕食量最大,应用Rogers的模型能较好地对试验结果进行模拟。尼氏钝绥螨对桔全爪不同虫态的取食不存在选择效应,纽氏钝绥螨则嗜食若螨和幼螨。两种捕食螨对桔全爪螨的数值反应表明,仅供给桔全爪螨雌成螨作为食物,对两种捕食螨都不利,尤其对尼氏钝绥螨更为明显。综上所述,两种捕食螨能比较有效地控制桔全爪螨种群,当猎物密度较高时,尼氏钝绥螨控制效果优于纽氏钝绥螨,但纽氏钝绥螨控制效果优于纽氏钝绥螨,但纽氏钝绥螨田间种群数量比尼氏钝绥螨稳定。柑桔园中存在其它补充食物时对这两种捕食敌有利。     

Intravenously injected sialidase inactivates attachment sites for lymphocytes on high endothelial venules

Blood-borne lymphocytes initiate entry into secondary lymphoid organs, such as peripheral lymph nodes (PN) and gut-associated Peyer's patches (PP), by a highly specific adhesive interaction between the lymphocytes and the endothelium of specialized blood vessels known as a high endothelial venules (HEV). The selectivity with which functional subpopulations of lymphocytes migrate into particular lymphoid organs is believed to be regulated by the expression of cell adhesion receptors and complementary ligands on lymphocytes and HEV, respectively. The entry of lymphocytes into PN and PP has clearly been shown to involve distinct receptor-ligand pairs. Employing the Stamper-Woodruff in vitro adhesion assay, which measures lymphocyte attachment to HEV in cryostat-cut sections of lymphoid organs, we have previously shown that treatment of PN sections with two different sialidases inactivates HEV-adhesive ligands, whereas treatment of PP tissue sections has no effect on HEV-adhesive function. We now report that in vivo exposure of HEV to sialidase (after i.v. injection of the enzyme) also selectively prevents subsequent in vitro attachment of lymphocytes to PN HEV but not to PP HEV. Consistent with this organ-selective impairment of HEV-adhesive function by sialidase, i.v. injection of the enzyme is shown to prevent short term lymphocyte accumulation within peripheral lymph nodes while having no significant effect on accumulation in PP, blood, or nonlymphoid organs. Histologic examination with the sialic acid-specific lectin from Limax flavus verified that i.v. injected sialidase effectively removes stainable sialic acid moieties from HEV in both PN and PP. This study confirms that sialic acid is required for the adhesive function of PN HEV-ligands. A role for sialic acid as either a recognition determinant or as a regulatory molecule can be envisioned. In view of the fact that many pathogens release sialidase and cause substantially elevated serum levels of this enzyme, the present observations may have pathophysiologic significance. One mechanism by which such pathogens may avoid destruction is to inactivate susceptible HEV-ligands and disrupt the entry of lymphocytes into lymphoid organs where immune responses against the pathogens would normally be initiated.     

H Efflux and Hexose Transport under Imposed Energy Status in Maize Root Tips

The relationship between changes in H⁺ flux and sugar transport in maize Zea mays L. DEA root tips have been investigated using two methods for controlling the cellular nucleotide level: (a) incubation in the presence of a glucose analog, the 2-deoxyglucose, which decreased the ATP level to less than 15% of its initial value within 60 minutes without changing the ADP and AMP levels; (b) an hypoxic treatment which also decreased the ATP level but with a concomitant rise in ADP and AMP. In both cases the rate of hexose transport was not modified until ATP had dropped to 70% of its initial value; then it decreased with the cellular ATP level. The residual uptake rate at very low ATP concentrations still represented 50% of the maximum rate with the dGlc treatment but only the diffusion rate in anoxia. H⁺ efflux was abolished in anoxia but not by the 2-deoxyglucose treatment, in spite of a lower cellular ATP concentration. Our results are consistent with an inhibition of H⁺-ATPase activity in anoxia by the high levels of cellular ADP and AMP, and provide in vivo evidence that sugar uptake is dependent upon the proton motive force rather than cellular ATP concentration. The absence of stimulation of H⁺ extrusion by ferricyanide in either normoxic or hypoxic conditions suggests that a redox system does not appear to contribute to H⁺ secretion under the conditions of this investigation.