Sequences of the Escherichia coli BtuB protein essential for its insertion and function in the outer membrane.

The Escherichia coli btuB gene encodes the outer membrane transporter for vitamin B12, the E colicins, colicin A, and bacteriophage BF23. Several series of mutant forms of BtuB resulting from the insertion of dipeptide sequences and from overlapping in-frame deletions and duplications were constructed. Strains expressing the variant genes in single and multiple copy numbers were analyzed for BtuB function, for the level of BtuB polypeptide in the outer membrane, and for changes in the outer membrane permeability barrier. Most dipeptide insertions had normal transport function and assembly in the membrane. Only 2 of the 27 deletions spanning residues 5 and 514 possessed transport function, and most of the remainder were not stably inserted in the membrane. Most duplications (19 of 21) retained transport function and were inserted in the outer membrane, although some were subject to proteolysis. Even long duplications containing as many as 340 repeated amino-terminal residues retained function, suggesting considerable plasticity in the sequence requirements for membrane insertion of BtuB. Expression of many deletion and duplication proteins conferred increased susceptibility to structurally unrelated inhibitors that are normally excluded by the outer membrane. These results could be consistent with the mutational disruption of extracellular loops or transmembrane segments of BtuB that constitute a gated channel, but the finding that alterations throughout the length of BtuB affect membrane permeability properties suggests that the altered proteins might perturb the outer membrane structure itself.     

Phenotypic features of breast cancer cells overexpressing ornithine-decarboxylase

Polyamines (PA) have been shown to be critical mediators of estradiol-induced breast cancer cell proliferation. This finding suggests that constitutive activation of the PA pathway may promote tumor progression, possibly leading to hormone independence. To test this hypothesis, we transfected hormone-responsive MCF-7 breast cancer cells with a complementary DNA coding for ornithine-decarboxylase (ODC), the first rate-limiting enzyme in PA biosynthesis. Marked ODC over-expression observed in stably transfected clones was associated with a selective increase in cellular putrescine content, while spermidine and spermine levels were not altered. ODC-overexpressing MCF-7 cells were resistant to the antiproliferative effects of low but not high concentrations of the enzyme inhibitor, α-difluoromethylornithine. In agreement with our hypothesis, sensitivity to the growth-promoting action of estradiol was reduced by approximately one third (P < 0.001) in ODC-overexpressing MCF-7 cells compared with vector-only transfected clones. Basal growth under anchorage-dependent conditions was only marginally increased by ODC overexpression (P = 0.048), while clonogenicity in soft agar was actually reduced. These data suggest that activation of PA biosynthesis may contribute in part to the acquisition of estrogen independence by breast cancer cells. Since only putrescine content was increased as a result of ODC overexpression, these data may underestimate the overall influence of the PA pathway on breast cancer phenotype. © 1995 Wiley-Liss, Inc.     

Health in China. From Mao to market reform.

After the Liberation by Mao Ze Dong''s Communist army in 1949, China experienced massive social and economic change. The dramatic reductions in mortality and morbidity of the next two decades were brought about through improvements in socioeconomic conditions, an emphasis on prevention, and almost universal access to basic health care. The economic mismanagement of the Great Leap Forward brought about a temporary reversal in these positive trends. During the Cultural Revolution there was a sustained attack on the privileged position of the medical profession. Most city doctors were sent to work in the countryside, where they trained over a million barefoot doctors. Deng Xiao Ping''s radical economic reforms of the late 1970s replaced the socialist system with a market economy. Although average incomes have increased, the gap between rich and poor has widened.     

Mechanisms of the actions of aromatase inhibitors 4-hydroxyandrostenedione, fadrozole, and aminoglutethimide on aromatase in JEG-3 cell culture

Selective inhibition of estrogen production with aromatase inhibitors has been found to be an effective strategy for breast cancer treatment. Most studies have focused on inhibitor screening and in vitro kinetic analysis of aromatase inhibition using placental microsomes. In order to determine the effects of different inhibitors on aromatase in the whole cell, we have utilized the human choriocarcinoma cell line, JEG-3 in culture to compare and study three classes of aromatase inhibitors, 4-hydroxyandrostenedione, fadrozole (CGS 16949A), and aminoglutethimide. Fadrozole is the most potent competitive inhibitor and aminoglutethimide is the least potent among the three. However, stimulation of aromatase activity was found to occur when JEG-3 cells were preincubated with aminoglutethimide. In contrast, 4-OHA and fadrozole caused sustained inhibition of aromatase activity in both JEG-3 cells and placental microsomes, which was not reversed even after the removal of the inhibitors. 4-OHA bound irreversibly to the active site of aromatase and caused inactivation of the enzyme which followed pseudo-first order kinetics. However, 4-OHA appears to be metabolized rapidly in JEG-3 cells. Sustained inhibition of aromatase induced by fadrozole occurs by a different mechanism. Although fadrozole bound tightly to aromatase at a site distinct from the steroid binding site, the inhibition of aromatase activity by fadrozole does not involve a reactive process. None of the inhibitors stimulated aromatase mRNA synthesis in JEG-3 cells during 8 h treatment. The stimulation of aromatase activity by AG appeared to be due to stabilization of aromatase protein. According to these results, 4-OHA and fadrozole would be expected to be more beneficial in the treatment of breast cancer patients than AG. The increase in aromatase activity by AG may counteract its therapeutic effect and might be partially responsible for relapse of breast cancer patients from this treatment.     

异色芋生物学特性观察

本文对观赏植物异色芋（ＣｏｌｏｃａｓｉａｈｅｔｅｒｏｃｈｒｏｍａＨ．ＬｉｅｔＺ．Ｘ．Ｗｅｉ）在昆明栽培环境下的生物学特性进行总结,为商品化栽培异色芋提供了理论依据,为其分类也提供了一定的有益补充。结果表明：一年生植株不开花,根茎也不产生分枝;二年生植株开花率为７３．６％,根茎平均分枝３．６条。异色芋３月上旬开始萌动,７月中旬抽花梗,８月上旬开花,１１月份地上部分枯萎,因此在昆明异色芋生育期约２６０ｄ。     

甘蔗和烟草幼叶原生质体的核酸含量与核酸酶活性及其影响因素

与幼叶组织相比,酶法新鲜分离的甘蔗和烟草幼叶原生质体内的ＲＮＡ、ＤＮＡ及总核酸含量均降低。其原因可能是刚游离的原生质体内酸性和碱性ＲＮＡ酶与ＤＮＡ酶等活性提高所致。甘蔗叶原生质体内的核酸降低量和ＲＮＡ酶与ＤＮＡ酶活性的增加程度均高于烟草。随用作渗透压稳定剂的甘露醇浓度增加,甘蔗和烟草叶原生质体的ＲＮＡ酶和ＤＮＡ酶活性均相应提高。其中以甘蔗叶原生质体的核酸酶活性增加水平较明显。在细胞壁降解产物的作用下,除了甘蔗原生质体内的ＲＮＡ酶活性略被促进外,其ＤＮＡ酶和烟草叶原生质体内的核酸酶均不受影响     

Secretion of unprocessed human surfactant protein B in milk of transgenic mice

Because of the apparent clinical importance of human pulmonary surfactant B (SP-B), the expression of SP-B was directed to the mammary gland of transgenic mice using previously characterized rat whey acidic protein (WAP) regulatory sequences. rWAP/SP-B mRNA was expressed specifically in the mammary gland, and ranged from 1 to 5% of the endogenous WAP mRNA levels. SP-B was detected immunologically in both tissue and milk. The transgene product had an apparent molecular weight of 40--45 kDa, corresponding to the predicted size of the SP-B proprotein. Incubation of an SP-B-enriched fraction of milk with cathepsin D in vitro produced 20--25 kDa species, consistent with cleavage of the amino terminal domain by cathepsin D. This was confirmed using antibodies specific to the carboxy-terminal domain of SP-B. However, the appearance of only the SP-B proprotein in milk suggests that cathepsin D is not involved in the in vivo processing of SP-B. The SP-B proprotein can be expressed in milk of transgenic mice without any observed effects on mammary gland morphology or lactation     

短盖巨脂鲤卵巢发育组织学研究

通过对短盖巨脂鲤各个生长时期卵巢组织学研究以及成熟卵超微结构观察,获得短盖巨脂鲤生长发育过程中卵巢发育规律;同时对卵母细胞核仁排出物与核质关系及在卵黄形成中的作用等问题作了初步探讨;并根据卵巢的卵母细胞组成确定了其产卵类型。     

东亚大都市学生头型的比较研究

为了研讨居住区域的气候条件和社会经济环境对头型的影响,采用国际通用的人体测量法,调查测量了东亚三个国家四个集团３４７２名６－１７岁学生的头长和头宽,经统计学处理求得其平均值、头指数,回归方程,并作性差和地区差检验,其结果表明：中国大连学生为特圆头型,菲律宾马尼拉学生为圆头型,地理位置在大连和马尼拉之间的日本东京的学生的头型也位于二者之间,生活富裕集团的头长和头宽明显大于生活贫穷集团的学生,但头型二     

Fe-deficiency stress response in Fe-deficiency resistant and susceptible subterranean clover: importance of induced H+ release

Plants can exhibit Fe-deficiency stress response when they areexposed to Fe-deficiency conditions. The relative importanceof the individual Fe-deficiency stress-response reactions, forexample, increased release of H⁺ from roots, enhanced root plasmamembrane-bound Fe³⁺ -reductase activity, and release of reductant,in Fe-deficiency resistance is not understood. To address thisproblem, the Fe-deficiency stress response of two cultivarsof subterranean clover (subclover), Koala (Trifolium brachycalycinumKatzn. and Morley) (Fe-deficiency resistant) and Karridale (T.subterraneum L.) (Fe-deficiency susceptible), were evaluated.The plants were cultured hydroponically at 0 (–Fe) and30 (+Fe) µM Fe³⁺ EDTA conditions. After 6 d Fe treatment,the –Fe Koala and Karridale decreased the pH of the nutrientsolution by 1.83 and 0.79 units, respectively, while the +Feplants increased the pH of the nutrient solution. The H⁺ -releaserate of the –Fe Koala determined 7 d after Fe treatmentinitiation was more than three times higher than that of the–Fe Karridale. The –Fe plants had a significantlyenhanced Fe³⁺ -reduction rate compared with the +Fe plants foreach cultivar, but the resistant cultivar did not exhibit ahigher root Fe³⁺ -reduction rate than the susceptible cultivarat each Fe treatment. Reductant release from the roots of subcloverwas negligible. These results indicate that Fe-deficiency-inducedH⁺ release may be the predominant factor influencing Fe-deficiencyresistance in subclover. Key words: Fe-deficiency, Fe³⁺ reduction, H⁺ release, stress response, Trifolium