钆和镱对人红细胞膜脂及膜蛋白的作用

利用荧光偏振,自旋标标顺磁共振波谱和激光拉曼技术研究了钆和镱对人红细胞膜结构和功能的影响。结果表明,低浓度的Ｇｄ３＋（０．５μｍｏｌ／Ｌ）对（Ｎａ＋＋Ｋ＋）－ＡＴＰ酶和Ｍｇ２＋－ＡＴＰ酶有轻微的激活作用,而随着其浓度的增大,则明显抑制酶的活性,Ｇｄ３＋与Ｙｂ３＋和人红细胞膜作用后,降低膜脂流动性,并使膜蛋白酰胺Ｉ＇－α螺旋振动强度减弱．     

Characterization of Maize Acetyl-Coenzyme A Carboxylase

Maize (Zea mays L.) leaf acetyl-CoA carboxylase (ACCase) was purified about 500-fold by ammonium sulfate fractionation and gel filtration and blue Sepharose affinity and anion-exchange chromatography. Most ACCase activity (85%) recovered from the anion-exchange column was found in a highly purified fraction (specific activity 5.5 [mu]mol acid-stable product min-1 mg-1) that consisted primarily of a single 227-kD biotinylated polypeptide. The fraction represented 29% of the original activity and was designated ACCase I. A second partially purified ACCase activity (ACCase II) eluted earlier during anion-exchange chromatography, contained a single biotinylated polypeptide of 219 kD, was poorly recognized by antiserum raised against the ACCase I polypeptide, and was less inhibited by the herbicides haloxyfop or sethoxydim than was ACCase I. ACCase I and II both utilized propionyl-CoA as substrate about 50% as effectively as acetyl-CoA, and neither utilized methylcrotonyl-CoA. Immunoprecipitation with antiserum and protein blotting of crude extracts of leaf, embryo, and endosperm tissue and suspension cells indicated that most ACCase activity in these tissues was immunologically similar and consisted of ACCase I. Only leaves contained significant amounts of the ACCase II polypeptide; however, no ACCase II polypeptide was found in isolated mesophyll chloroplasts. The ACCase I and II polypeptides appear to be subunits of distinct ACCase isoforms.     

Aluminum Effects on Calcium (45Ca2+) Translocation in Aluminum-Tolerant and Aluminum-Sensitive Wheat (Triticum aestivum L.) Cultivars (Differential Responses of the Root Apex versus Mature Root Regions)

The influence of Al exposure on long-distance Ca2+ translocation from specific root zones (root apex or mature root) to the shoot was studied in intact seedlings of winter wheat (Triticum aestivum L.) cultivars (Al-tolerant Atlas 66 and Al-sensitive Scout 66). Seedlings were grown in 100 [mu]M CaCl2 solution (pH 4.5) for 3 d. Subsequently, a divided chamber technique using 45Ca2+-labeled solutions (100 [mu]M CaCl2 with or without 5 or 20 [mu]M AlCl3, pH 4.5) was used to study Ca2+ translocation from either the terminal 5 to 10 mm of the root or a 10-mm region of intact root approximately 50 mm behind the root apex. The Al concentrations used, which were toxic to Scout 66, caused a significant inhibition of Ca2+ translocation from the apical region of Scout 66 roots. The same Al exposures had a much smaller effect on root apical Ca2+ translocation in Atlas 66. When a 10-mm region of the mature root was exposed to 45Ca2+, smaller genotypic differences in the Al effects effects on Ca2+ translocation were observed, because the degree of Al-induced inhibition of Ca2+ translocation was less than that at the root apex. Exposure of the root apex to Al inhibited root elongation by 70 to 99% in Scout 66 but had a lesser effect (less than 40% inhibition) in Atlas 66. When a mature root region was exposed to Al, root elongation was not significantly affected in either cultivar. These results demonstrate that genotypic differences in Al-induced inhibition of Ca2+ translocation and root growth are localized primarily in the root apex. The pattern of Ca2+ translocation within the intact root was mainly basipetal, with most of the absorbed Ca2+ translocated toward the shoot. A small amount of acropetal Ca2+ translocation from the mature root regions to the apex was also observed, which accounted for less than 5% of the total Ca2+ translocation within the entire root. Because Ca2+ translocation toward the root apex is limited, most of the Ca2+ needed for normal cellular function in the apex must be absorbed from the external solution. Thus, continuous Al disruption of Ca2+ absorption into cells of the root apex could alter Ca2+ nutrition and homeostasis in these cells and could play a pivotal role in the mechanisms of Al toxicity in Al-sensitive wheat cultivars.     

Identification and Characterization of a Biodegradative Form of Threonine Dehydratase in Senescing Tomato (Lycopersicon esculentum) Leaf

Threonine dehydratase (TD; EC.4.2.1.16) is a key enzyme involved in the biosynthesis of isoleucine. Inhibition of TD by isoleucine regulates the flow of carbon to isoleucine. We have identified two different forms of TD in tomato (Lycopersicon esculentum) leaves. One form, present predominantly in younger leaves, is inhibited by isoleucine. The other form of TD, present primarily in older leaves, is insensitive to inhibition by isoleucine. Expression of the latter enzyme increases as the leaf ages and the highest enzyme activity is present in the old, chlorotic leaves. The specific activity of the enzyme present in older leaves is much higher than the one present in younger leaves. Both forms can use threonine and serine as substrates. Whereas TD from the older leaves had the same Km (0.25 mM) for both substrates, the enzyme from the young leaves preferred threonine (Km = 0.25 mM) over serine (Km = 1.7 mM). The molecular masses of TD from the young and the old leaves were 370,000 and 200,000 D, respectively. High levels of the isoleucine-insensitive form of threonine dehydratase in the older leaves suggests an important role of threonine dehydratase in nitrogen remobilization in senescing leaves.     

Interrelationships among fluorometric analyses of spermatozoal function, classical semen quality parameters and the fertility of frozen-thawed bovine spermatozoa

Cryopreserved spermatozoa from 8 bulls were used to examine the interrelationships among flow cytometric spermatozoal quality assessments and classical semen quality parameters and nonreturn rate estimates of fertility. The integrity of the sperm cell membrane and the functional capacity of the mitochondria were quantified by flow cytometry after concurrent staining with carboxydimethylfluorescein diacetate (CDMFDA), propidium iodide (PI), and rhodamine 123 (R123). For each sample a total of 10,000 stained spermatozoa were simultaneously quantified for the intensity of their green and red fluorescence. Three straws from each bull were each examined initially and following incubation at 37 degrees C for 3 hours to assess the rate of senescence. The proportion of spermatozoa retaining membrane integrity and having functional mitochondria, as determined by CDMFDA and R123 staining, were compared with classical semen quality assessments (sperm motility, acrosomal status, cellular and head morphology, presence of vacuoles/craters and cytoplasmic droplets) and with fertility (nonreturn to estrus rates). For individual ejaculates nonreturn rates, the range was from 61.8 to 78.8%, whereas the cumulative rates of several ejaculates for each bull ranged from 71.3 to 83.5%. The proportion of spermatozoa with functional membranes and mitochondria were positively correlated with the percentage of spermatozoa with normal morphology (r=0.82; P=0.01) and motility after 4 hours of incubation (r=0.78; P=0.02), but not with the estimates of fertility. The actual number of spermatozoa per straw staining with CDMFDA and R123 after 4 hours of incubation at 37 degrees C was correlated with the percentage of spermatozoa with normal morphology (r=0.73; P=0.04). Multiple regression equations indicated that combinations of semen quality measurements could be useful in estimating fertilizing potential.     

东方鲎消化道上皮的超微结构观察

本文利用透射电镜对2只成年健康东方鲎消化道上皮的超微结构进行观察。文中重点描述了从食道至直肠的上皮细胞超微结构的主要特点,并对其结构与功能之间的关系进行了初步的讨论。     

藻－菌生态系统代谢功能的生态学研究

在室内模拟条件下,研究了一些生态因子对藻－菌（Ａ＋Ｂ）生态系统代谢有机碳（Ｃ６Ｈ１２Ｏ６）、ＮＨ３－Ｎ和无机磷（ＩＰ）的影响．研究结果表明,当藻－菌生态系统中藻（Ａ）或菌（Ｂ）的起始数量一定时,其代谢Ｃ６Ｈ１２Ｏ６的速率,随与之组合的Ｂ或Ａ的起始数量增加（数量比则相应降低）而增加．在光照和黑暗条件下,Ａ＋Ｂ系统代谢上述３种营养物质的速率均有一定的差异．黑暗下Ｃ６Ｈ１２Ｏ６的平均代谢速率较光照下高１２．３％（Ｐ＜０．０５）,ＩＰ和ＮＨ３－Ｎ的平均代谢速率则分别较光照下低１４．４％（Ｐ＜０．０５）和１６．２％（Ｐ＜０．００１）．在Ａ＋Ｂ系统和Ａ、Ｂ单培养物中,３种营养物质的代谢速率均随有机负荷量增加而增加,而且Ａ＋Ｂ系统的代谢速率分别高于单培养的Ａ和Ｂ,其中ＮＨ３－Ｎ代谢尤为显著．文章还就生态系统结构与功能的关系问题进行了讨论．