激光光漂恢复技术测定林蛙卵第一次卵裂前卵表面的运动

激光光漂恢复技术测定了异硫氰基荧光素标记的林蛀卵表面分子在第一次卵裂前的运动。发现固着在玻片上的剥离“细胞膜”的分子运动形式为扩散。扩散系数为(4.6±1.3)×10~(-12)cm~2/s,可动部份为15%。完整卵子上的分子运动形式为流动。细胞膜在不停地流动着。它可能起着协助细胞质运动的作用。细胞膜流动的速度随时间而异,卵裂前不久,在大多数的卵子上,出现两个流动较慢的谷,少数细胞只测到一个谷。这可能与光漂起始时间,光斑与未来分裂沟的距离,和卵子间的差异有关。也讨论了这种速度变化与表面收缩波的关系。     

Effects of sodium butyrate on human colonic adenocarcinoma cells. Induction of placental-like alkaline phosphatase

We have examined the effects of the "differentiating agent," sodium butyrate, on the induction of alkaline phosphatase in human colonic tumor cell line LS174T. Culture of these cells in the presence of 2 mM butyrate caused this activity to increase from less than 0.0001 unit/mg of protein to greater than 0.7 unit/mg of protein over an 8-day period. This induction proceeded in a nonlinear fashion with a lag time of 2-3 days occurring before enzymatic activity began to rise. These increases in activity were accompanied by elevations in the content of a placental-like isozyme of alkaline phosphatase as demonstrated by "Western" immunoblots. Dome formation, indicative of differentiation in cultured cells, also required 3 days treatment with butyrate before becoming evident. The rate of biosynthesis of the enzyme, examined using metabolic labeling with L-[35S]methionine and immunoprecipitation, was found to increase continuously between days 2 and 6 of butyrate treatment. "Northern" blot analysis indicated that treatment of these cells with butyrate caused greater than 20-fold induction of a 2700-base mRNA that hybridized to a cDNA probe for placental alkaline phosphatase. The mRNA for alkaline phosphatase produced by these cells upon butyrate treatment was approximately 300-400 bases smaller than the mRNA for alkaline phosphatase found in placenta. Human small intestine also contained two mRNAs that hybridized relatively weakly with the placental alkaline phosphatase probe. These results indicate that a placental alkaline phosphatase-like protein and mRNA are induced by butyrate in LS174T cells with a time course consistent with cellular differentiation preceding induction.     

电刺激大鼠延髓头端腹外侧区对交感节前神经元单位放电的影响

本实验用氨基甲酸乙酯麻醉和箭毒化的雄性大鼠,细胞外记录脊髓胸2节段的交感节前神经元(SPN)单位放电,电刺激同侧颈交感干,逆向激活 SPN,以确定所记录的神经元为交感节前神经元。共分析了80个 SPN 单位放电,其中有自发活动和无自发活动的单位各40个。SPN 轴突传导速度为0.59—3.75m/s。实验观察到电刺激同侧延髓头端腹外侧区(Rostralventrolateral medulla:RVL)可兴奋多数有自发活动的 SPN(19/25),并可使少数静止SPN 产生诱发反应(4/23),潜伏期为6—115ms。电刺激对侧 RVL 结果类似:多数自发活动的 SPN(6/9)呈兴奋反应,及少数静止 SPN(3/17)产生诱发反应,潜伏期为11—105ms。表明 RVL 对双侧 SPN 有兴奋性影响。     

Expression of C4-like photosynthesis in several species of Flaveria

Abstract Photosynthetic metabolism was investigated in leaves of five species of Flaveria (Asteraceac), all previously considered to be C₄ plants. Leaves were exposed to ¹⁴CO₂ for different intervals up to 16s. Extrapolation of ¹⁴C-product curves to zero time indicated that only F. trinervia and F.bidentis assimilated atmospheric CO₂ exclusively through phosphoenolpyruvate carboxylase. The proportion of direct fixation of ¹⁴CO₂ by ribulose-I, 5-bisphosphate carboxylase/oxygenase (Rubisco) ranged from 5 to 10% in leaves of F. australasica. F. palmeri and F. vaginata. Protoplasts of leaf mesophyll and bundle sheath cells were utilized to examine the intercellular compartmentation of principal photosynthetic enzymes. Leaves of F. australasica, F. palmeri and F. vaginata contained 5 to 7% of the leaf's Rubisco activity in the mesophyll cells, while leaves of F. trinervia and F. bidentis contained at most 0.2 to 0.8% of such activity in their mesophyll cells. Thus, F. trinervia and F. bidentis have the complete C₄ syndrome, while F. australasica, F. palmeri and F. vaginata are less advanced, C₄-like species.     

Insulin-stimulated alpha-(methyl)aminoisobutyric acid uptake in skeletal muscle. Evidence for a short-term activation of uptake independent of Na+ electrochemical gradient and protein synthesis.

1. The present study was designed to explore the mechanisms by which insulin stimulates system A of amino acid transport in extensor digitorum longus (EDL) muscles, by using a system A analogue, alpha-(methyl)aminoisobutyric acid (MeAIB). 2. Insulin stimulation of MeAIB uptake was noted after only 30 min of incubation and was maximal at 60 min. Kinetics of the insulin effect on MeAIB uptake were characterized by an increased Vmax. without modification of Km for MeAIB. 3. Incubation of EDL muscles with cycloheximide for 90 min did not modify MeAIB uptake in either the presence or the absence of insulin, indicating the independence of insulin action from protein synthesis de novo. Incubations for 180 min with cycloheximide caused a decrease in basal MeAIB uptake; however, the percentage stimulation of amino acid transport by insulin was unaltered. Basal MeAIB uptake was increased by incubation for 180 min, but under these conditions no change in the percentage effect of insulin was found. 4. Ouabain, gramicidin D, or both, markedly decreased basal MeAIB uptake by EDL muscle, but the percentage effect of insulin was unaltered. 5. We conclude that insulin action on amino acid transport through system A in muscle is rapid, is characterized by an increased Vmax., and is independent of protein synthesis de novo and the Na+ electrochemical gradient. Our data are compatible with insulin acting directly on the system A transporter.     

Distribution of Metabolites and Enzymes of Nitrogen Metabolism between the Mesophyll and Paraveinal Mesophyll of Non-Nodulated Glycine max

The distribution of amino acids and key enzymes involved innitrogen metabolism was determined in mesophyll cells (MC),mesophyll protoplasts (MP), and paraveinal mesophyll protoplasts(PVMP) isolated from fully expanded trifoliolate leaves of non-nodulatedsoybean. Qualitative and quantitative differences were foundin the distribution of amino acids, with MP containing the highestconcentrations. Activity of nitrate reductase, glycolate oxidase,glutamine synthetase and glutamate dehydrogenase was measuredin both tissue types and differences in activities between thetissue types were seen. PVMP had high glutamate dehydrogenaseactivity when compared to MP. Activities of glycolate oxidaseand glutamine synthetase were much higher in MP on a protoplastbasis while nitrate reductase activity was similar between thetwo protoplast types. These results, on the distribution ofmetabolites and associated enzymes, are discussed as to theirpossible significance to nitrogen metabolism in the soybeanleaf. Key words: Amino acids, glutamate dehydrogenase, Glycine max, nitrate reductase, nitrogen metabolism, paraveinal mesophyll, protoplasts     

凝集素抑制林蛙卵裂沟新膜外露的作用

剥去受精膜的林蛙卵分裂时,分裂沟中的新膜会暴露出来。林蛙老膜上有大量均匀分布的麦胚和大豆凝集素受体。卵裂前,将剥去受精膜的蛙卵浸于上述的凝集素溶液中,新膜的外露就被抑制。凝集素愈浓,浸泡时间愈长,抑制愈大。在这些卵的表面可看到一层较厚的由凝集素引起的外被。碱处理过的受精卵表面,凝集素受体减少,凝集素抑制新膜外露的作用亦减弱,由凝集素引起的外被亦薄。凝集素是多价的,会在细胞表面产生交链,形成“外骨骼”,抑制新膜外露。凝集素也可通过受体,影响微丝,产生作用。     

Molecular cloning of rat intestinal mucin. Lack of conservation between mammalian species

We have prepared antisera to deglycosylated rat intestinal mucin and used it to obtain immunoreactive clones from a rat jejunum cDNA library. Four of these clones were sequenced, and all were found to be partial cDNAs that contained 18-base pair tandem repeats characteristic of a mucin. These cDNAs encoded a repetitive peptide with a consensus sequence of TTTPDV. Thus, they bear little resemblance to either of the two human intestinal mucin cDNAs isolated previously (Gum, J. R., Byrd, J. C., Hicks, J. W., Toribara, N. W., Lamport, D. T. A., and Kim, Y. S. (1989) J. Biol. Chem. 264, 6480-6487 and Gum, J. R., Hicks, J. W., Swallow, D. M., Lagace, R. E., Byrd, J. C., Lamport, D. T. A., Siddiki, B., and Kim, Y. S. (1990) Biochem. Biophys. Res. Commun. 171, 407-415). One of these rat mucin clones, designated RMUC 176, was chosen for further analysis. This clone recognized a band of approximately 9 kilobases when used to probe RNA blots. A strong hybridization band was present using rat small intestine and colon RNA but was not detectable when RNA isolated from heart, liver, or kidney was tested. The RMUC 176 clone and the two previously isolated human intestinal mucin cDNA clones were used to probe blots prepared from BamHI-digested DNA of various species. Here, the human probes detected fragments present only in human and chimpanzee DNA, whereas the RMUC 176 clone recognized fragments only in rat and mouse DNA. Thus, the repetitive portions of intestinal mucin genes are apparently not well conserved between phylogenetically distant species.     

The human MUC2 intestinal mucin has cysteine-rich subdomains located both upstream and downstream of its central repetitive region.

The human MUC2 mucin is a large secretory glycoconjugate that coats the epithelia of the intestines, airways, and other mucus membrane-containing organs. Previous work has shown that this mucin contains an extended tandem repeat-containing domain rich in Thr and Pro. In the present work we describe two additional regions of this mucin located both upstream and downstream of the tandem repeat array. The carboxyl-terminal domain contains 984 residues and can be divided into mucin-like (139 residues) and cysteine-rich (845 residues) subdomains. This latter subdomain exhibits varying degrees of sequence similarity to a wide range of mucins and mucin-like proteins including those isolated from rats, pigs, cows, and frogs. We also report here the sequence of 1270 residues lying immediately upstream of the tandem repeats. This region contains a repetitive, mucin-like subdomain and a second cysteine-rich stretch of more than 700 residues. Both cysteine-rich subdomains of this mucin have sequence similarity with von Willebrand factor, a serum protein that exists as a disulfide-linked polymer. This suggests that these cysteine-rich subdomains are important in the catenation of mucin monomers into oligomers, the structures that confer viscoelasticity upon mucus.