Affinity labeling of spinach phosphoribulokinase subsequent toS-methylation at Cys16

The chloroplast enzyme phosphoribulokinase is reversibly deactivated by oxidation of Cys16 and Cys55 to a disulfide. Although not required for catalysis, Cys16 is an active-site residue positioned at the nucleotide-binding domain (Porter and Hartman, 1988). The hyperreactivity of Cys16 has heretofore limited further active-site characterization by chemical modification. To overcome this limitation, the partially active enzyme,S-methylated at Cys16, has been probed with a potential affinity reagent. Treatment of methylated enzyme with bromoacetylethanolamine phosphate results in essentially complete loss of catalytic activity. Inactivation follows pseudo-first-order kinetics and exhibits a rate saturation with an apparentK _d of 3–4 mM. ATP, but not ribulose 5-phosphate, affords substantial protection. Complete inactivation correlates with incorporation of 1 mol of [¹⁴C]reagent per mole of enzyme subunit. Amino acid analysis of the [¹⁴C]-labeled enzyme demonstrates that only cysteine is modified, and mapping of tryptic digests shows that Cys55 is a major site of alkylation. These results indicate that Cys55 is also located in the ATP-binding domain of the active-site.     

大鼠肝癌模型CBRH—3的建立及其生物学特性

用ＤＥＮＡ诱发近交系Ｗｉｓｔａｒ大鼠,经三个月后得原发性肝癌,移植于同品系幼鼠,从而建立了 一株染色体众数正常,ＡＥＰ阳性的大鼠移植性肝癌模型,命名为ＣＢＲＨ－３,病理鉴定为肝细胞型肝 癌。至今已传至６０余代,目前生长稳定。     

气候变化导致青藏高原马鹿种群适应性分布退缩：以类乌齐马鹿国家级自然保护区为例

近50年青藏高原的气候变化速率是全球平均值的2倍,对高原有蹄类的种群分布和多样性维持带来严重影响。本研究以西藏类乌齐马鹿国家级自然保护区的马鹿种群为例,通过2013年和2021年对马鹿和牦牛种群数量、分布的调查,并整合了物种分布模型和种群动态模型,评估了当前和未来气候变化及人类活动(放牧、道路、居民点等)对马鹿种群适应性分布的影响。研究表明,马鹿种群在2013—2021年由890头增加到1 400头,根据种群增长模型预计在2050年马鹿种群数量将达到1 735头,但其适宜栖息地在2050年代下降43.4%,2070年代下降5.1%,表明马鹿种群增长与适宜栖息地缩小之间的冲突将不利于马鹿种群的可持续发展。同时,当前马鹿与牦牛栖息地重合率为19%,2050年代为60%,2070年代为37%,且牦牛与马鹿存在食物竞争,这在一定程度上减少了马鹿原有的适宜栖息地。为保护马鹿,建议减少牦牛的饲养量1 000～1 500头。本研究将种群增长模型、种间竞争关系与物种分布模型整合,把气候变化对物种的影响延伸到种群层面,对其他物种的保护具有借鉴意义。     

脓青素对光抑制条件下菠菜叶绿体的保护作用

在有氧条件下,脓青素可以缓解强光对菠菜叶绿体电子传递的抑制作用。加入解联剂尼日利亚菌素消除跨膜质子梯度会加剧叶绿体的光抑制,但脓青素的保护作用并不消失。脓青素对光系统Ⅰ与光系统Ⅱ均表现出保护作用,但对ＰＳⅡ的保护在光抑制初期较明显;在厌氧条件下,脓青素加剧叶绿体的光抑制,引起ＤＣＩＰ光还原与水到ｐ－ＢＱ电子传递活力的降低。推测脓青素可能通过促进细胞色素ｂ５５９介导的ＰＳⅡ循环电子传递,减轻了叶绿体的光抑制。     

Syncytium-inducing (SI) phenotype suppression at seroconversion after intramuscular inoculation of a non-syncytium-inducing/SI phenotypically mixed human immunodeficiency virus population.

Two distinct biological phenotypes of human immunodeficiency virus (HIV) have been described: the non-syncytium-inducing (NSI) phenotype, best characterized by the inability to infect MT-2 cells, and the syncytium-inducing (SI) phenotype, with the ability to infect MT-2 cells. The earliest virus population observed following HIV transmission is generally of the NSI phenotype, even after exposure to inocula of mixed NSI/SI phenotype. In this study, the issue of intrapatient selection of virus phenotype following transmission was addressed by studying two cases of accidental transmission. A comparison of the sequences of the V1-V2 and the V3 coding regions of the envelope gene and the p17 region of the gag gene showed that the donor-recipient pairs were tightly clustered in all gene segments, but away from local and published transmission controls. The intrasample variation of the p17 sequence was greater in the recipients and smaller in the donors than that of the V3 region sequence, indicating selection of V3 at transmission. In these transmission cases, the effects of an intravenous inoculation of a small quantity of blood containing predominantly SI V3 sequences (6 of 8 clonal sequences) were compared with those of an intramuscular inoculation of a large quantity of blood containing predominantly NSI viruses (14 of 16 clonal sequences). Both SI and NSI V3 regions were demonstrated to be phenotypic expressions of genetically related viral strains. The inoculation of the predominantly SI virus population resulted in the persistence of an SI virus population in the recipient and a rapid CD4+ T-cell decline. The inoculation of the predominantly NSI population resulted in a selective amplification of SI viruses before seroconversion, followed by a suppression of SI viruses at seroconversion and a rapid decline of CD4+ T-cell numbers. These data suggest that the suppression of SI viruses can be accomplished following the development of HIV-specific immunity and that the ability to suppress SI viruses does not prevent the development of immunodeficiency.     

Characterization of the gene for the chromosomal dihydrofolate reductase (DHFR) of Staphylococcus epidermidis ATCC 14990: the origin of the trimethoprim-resistant S1 DHFR from Staphylococcus aureus?

The gene for the chromosomally encoded dihydrofolate reductase (DHFR) of Staphylococcus epidermidis ATCC 14990 has been cloned and characterized. The structural gene encodes a polypeptide of 161 amino acid residues with a calculated molecular weight of 18,417. This trimethoprim-sensitive (Tmps) DHFR, SeDHFR, differs in only three amino acids (Val-31-->Ile, Gly-43-->Ala, and Phe-98-->Tyr) from the trimethoprim-resistant (Tmpr) S1 DHFR encoded by transposon Tn4003. Since in addition the S. epidermidis gene also forms part of an operon with thyE and open reading frame 140 as in Tn4003, the chromosomally located gene encoding the Tmps SeDHFR is likely to be the molecular origin of the plasmid-located gene encoding the Tmpr S1 DHFR. Site-directed mutagenesis and kinetic analysis of the purified enzymes suggest that a single Phe-->Tyr change at position 98 is the major determinant of trimethoprim resistance.     

四川自贡大山铺成渝龟科—新属

描述了产自四川自贡大山铺恐龙化石坑中的三件龟甲标本,命名为一新属新种—周氏四川龟（Sichuanchelyschowigen．etsp．nov．）。该属以椎盾极横宽,中部缘盾极狭长为主要特征,它代表了成渝龟科中一类较特别的类型。     

Construction of a recombinant human GM-CSF/MCAF fusion protein and study on its in vitro and in vivo antitumor effects

A novel cytokine fusion protein was constructed by fusing granulocyte macrophage colony stimulat-ing factor (GM-CSF) with monocyte chemotactic activating factor (MCAF), which acts as a factor directing effector cells (monocytes) to a target site. The recombinant human GM-CSF/MCAF fusion protein could sustain the growth of GM-CSF-dependent cell line TF1 and was chemotactic for monocytes. The in vitro antitumor effect showed that rhGM-CSF/MCAF could activate monocytes to inhibit the growth of several human tumor cell lines, including a promyelocyte leukemia cell line HL-60, a lung adenocarcinoma cell line A549, a hepatoma cell line SMMC-7721 and a melanoma cell line Bowes. Furthermore, the cytotoxicity of monocytes activated by rhGM-CSF/MCAF against HL-60 and A549 was greater than that activated by GM-CSF or MCAF alone, even greater than that activated by a combina-tion of GM-CSF and MCAF, suggesting that the fusion protein has synergistic or enhanced effects. The in vivo anti-tumor effect indicated that     

糖皮质激素及其他甾体激素对大鼠下丘脑薄片释放精氨酸加压素的影响

本工作采用离体孵育技术,观察大鼠下丘脑薄片（含有室旁核和视上核）释放精氨酸加压素（ＡＶＰ）和糖皮质激素（ＧＣ）及其他甾体激素对ＡＶＰ释放的快速影响。结果如下：（１）大鼠下丘脑薄片经过９０ｍｉｎ的恢复之后,在长达６ｈ的孵育过程中能够相当稳定地释放ＡＶＰ,释放量为９．０６±１．２３ｐｇ／ｍｉｎ;（２）皮质酮（Ｂ）在２０ｍｉｎ内可明显地抑制ＡＶＰ的释放,在１０－７—１０－４ｍｏｌ／Ｌ范围内呈剂量－效应关系;（３）在同一剂量（１０－６ｍｏｌ／Ｌ）,皮质醇、１７β－雌二醇和睾丸酮也可快速地抑制ＡＶＰ的释放,而相同剂量的地塞米松、醛固酮、孕酮、ＲＵ４８６和胆固醇却无此效应;（４）ＲＵ４８６（１０－７—１０－３ｍｏｌ／Ｌ）对ＡＶＰ的释放没有影响,但却能（１０－５—１０－３ｍｏｌ／Ｌ）部分地阻断Ｂ的快速抑制效应。这些结果表明,ＧＣ对大鼠下丘脑ＡＶＰ的释放具有不通过传统的基因组机制的快速抑制效应,此种抑制效应可能与ＧＣ的负反馈调节作用有关。