Characterization and chemical properties of phosphoribosylamine, an unstable intermediate in the de novo purine biosynthetic pathway

Incubation of [1-13C]-5-phosphoribosyl pyrophosphate ([1-13C]PRPP) and glutamine with PRPP amidotransferase results in rapid production and disappearance of two new resonances at 89.3 and 85.9 ppm. These resonances coincide with two of the products produced upon incubation of [1-13C]ribose 5-phosphate with NH3. Extensive NMR studies (15N and 1H-13C chemical shift correlation spectra) have allowed assignment of these resonances to beta- and alpha-phosphoribosylamine. These studies represent the first spectral observations of this chemically reactive intermediate. The rate of interconversion of alpha- to beta-phosphoribosylamine as a function of pH has been determined by saturation and inversion-transfer NMR methods. The rate of formation of 5-phosphoribosylamine (PRA) from ribose 5-phosphate and NH3 and its rate of decomposition as a function of pH have been determined with a glycinamide ribonucleotide synthetase trapping system fashioned after earlier studies of Nierlich and Magasanik [Nierlich, D. P., & Magasanik, B. (1965) J. Biol. Chem. 240, 366]. Phosphoribosylamine has a t1/2 = 38 s at 37 degrees C and pH 7.5. The pH-independent equilibrium constant for ribose 5-phosphate and NH3 with phosphoribosylamine has been established, 2.5 M-1, by use of these rate constants as well as by NMR methods. This equilibrium constant and the rates of nonenzymatic interconversion of alpha- and beta-PRA provide essential background for studying the mechanism of glycinamide ribonucleotide synthetase and investigating the possibility of channeling phosphoribosylamine between this enzyme and the first enzyme in the purine pathway.     

Variation in crypt size and its influence on the analysis of epithelial cell proliferation in the intestinal crypt.

The standard model of epithelial cell renewal in the intestine proposes a gradual transition between the region of the crypt containing actively proliferating cells and that containing solely terminally differentiating cells (Cairnie, Lamerton and Steel, 1965 a, b). The experimental justification for this conclusion was the gradual decrease towards the crypt top of the measured labeling and mitotic indices. Recently, however, we have proposed that intestinal crypts normally undergo a replicative cycle so that at any time in any region of the intestine, crypts will be found to have a wide range of sizes. We show here that if this intrinsic size variation is taken into account, then a sharp transition between the proliferative and nonproliferative compartments of individual intestinal crypts is consistent with the labeling and mitotic index distributions of mouse and rat jejunal crypts. Thus there is no need to invoke the region of gradual transition from proliferating to nonproliferating cells as is done in the standard model. The position of this sharp transition is estimated for both the mouse and rat. Experiments to further test our model are suggested and the significance of the results discussed.     

The stereochemical course of phosphoryl transfer catalyzed by herpes simplex virus type I-induced thymidine kinase

Herpes simplex virus type I (HSV-I)-induced thymidine kinase has been shown to catalyze phosphoryl transfer from adenosine 5'-[gamma-(S)-16O,17O,18O]triphosphate to thymidine with inversion of configuration at phosphorus. The simplest interpretation of this result is that phosphoryl transfer occurs by a single in-line group transfer between ATP and thymidine within the ternary enzyme complex.     

血友病患者血清中淋巴腺病病毒/人T细胞Ⅲ型病毒抗体检测

对浙江省1982～1984年注射了美国产浓缩Ⅶ因子制剂的18例血友病患者,用酶联免疫吸附法(ELTSA)检测了血清中淋巴腺病病毒/人T细胞Ⅲ型病毒(LAV/HTLV-Ⅲ)抗体,发现4例阳性,并经免疫荧光试验和Western印迹法证实。2例应用了国产浓缩Ⅷ因子者抗体阴性。一例从美国来华旅游死于艾滋病者,LAV/HTLV-Ⅲ抗体阳性。本研究证明,LAV/HTLVⅢ病毒巳通过美国生产的Ⅷ因子制剂传入中国。     

呼吸链底物和抑制剂对线粒体内膜流动性的影响

用DPH和ANS标记大鼠肝线粒体内膜,以稳态荧光偏振法,研究了呼吸链底物和抑制剂对内膜流动性的影响。1.苹果酸+谷氨酸、琥珀酸分别为底物,均能引起内膜流动性增加。2.琥珀酸对含心磷脂的脂质体的膜流动性无影响。3.在鱼藤酮存在的条件下,苹果酸+谷氨酸对内膜流动性的增加作用消失,但琥珀酸的作用仍然存在。有氰化钾时则琥珀酸的作用消失。4.不论外加底物存在与否,鱼藤酮使内膜的流动性下降,而氰化钾则使之增加。抗霉素A亦可使内膜的流动性增加。上述结果表明:线粒体内膜流动性与其功能密切相关。电子沿呼吸链传递使线粒体内膜流动性增加,这种变化可能与呼吸链成分的氧化还原态有关。     

HBsAg合成肽段的免疫源性和抗肽血清与天然HBsAg的结合测定

我们将三种乙型肝炎表面抗原的合成肽段在联结载体或不接载体的情况下,分别制备成4种免疫原对兔子进行了免疫。大部分兔子都产生了抗肽抗体。其中抗P_(122-48)(auw)与抗P_(122-148)(adw)都能与天然HBsAg反应,而抗P_(122-148)(adw)的抗HBs活力比文献报道的都高,通过结构分析表明:含有天然蛋白上免疫显性区域的免疫原是合成疫苗的理想选者。     

普通烟草和黄花烟草及体细胞杂种过氧化物酶同工酶等电聚焦电泳

日本学者长尾照义(1978)用原生质体融合获得普通烟草与黄花烟草的体细胞杂种植株。1980年陈家玉等在国内首先获得普通烟草(Copus Yeusuku No.4)和黄花烟草(Yellow Flower)的体细胞杂种植株。之后,中国农科院烟草所(1981)也得到相同的结果。陈家玉等(1983)对上述杂种进行了形态学、细胞学和同工酶的分析并取得一定的结果。Dlineee等(1975)分析比较了用等电聚焦技术分离的过氧     

用三维图象量测卵裂前蛙卵膜分子的三维运动

两栖类卵第一次卵裂前,缩时电影显示出卵表面有收缩波。由于卵的体积未变,在收缩时卵的高度必然增加。Sawai(1978)利用棱镜侧面摄取了蝾螈卵轮廓的高度变化,证实了卵裂前卵最高处的高度确有增加。但这一方法不能测知整个卵表面各处的高度变化,而且仅是二维的。在林蛙卵上,我们用荧光漂白恢复技术发现第一次卵裂前卵表面分子有规律性的流动,推测这是卵球的张弛。为了进一步     

绿茶抗氧化剂成分抑制突变作用的初步研究

绿茶水溶性提取物及茶叶中抗氧化剂成份具有明显的抑制AFB_1及Bap诱导的鼠伤寒沙门氏菌回复突变作用。这种抗氧化剂成份还可以抑制AFB_1和Bap诱导的V79细胞基因正向突变,以及AFB_1诱导的V79细胞SCE和染色体畸变。本实验结果提示,绿茶中抗氧化剂成份可能对AFB_1及Bap的致癌性具有抑制作用。本文就茶叶抗氧化剂抑制突变的可能机制进行了初步讨论。