The radiolysis of tryptophan and leucine with32Pβ-radiation

Summary We have extended earlier experiments on the radiolysis of DL-tryptophan using³²P-radiation to longer reaction times, observing complete destruction of the tryptophan by secondary, non-radiolytic processes. We have also undertaken the irradiation of DL-leucine with³²P's at -196°, achieving radiolyses to the extents of ca. 20–30%, but observing no concomittant asymmetric bias. The implications of these observations are discussed with regard to the Vester-Ulbricht mechanism for the origin of optical activity.     

Computer programs for analysis of nucleic acid hybridization, thermal denaturation, and gel electrophoresis data.

Computer programs for the analysis of data from techniques frequently used in nucleic acids research are described. In addition to calculating non-linear, least-squares solutions to equations describing these systems, the programs allow for data editing, normalization, plotting and storage, and are flexible and simple to use. Typical applications of the programs are described.     

Sequence composition of the template-active fraction of rat liver chromatin.

Rat liver chromatin has been separated into nuclease-sensitive and -resistant fractions after mild digestion with DNAase II. The nuclease-sensitive material is further fractionated into Mg2+ -soluble and -insoluble chromatin fractions. The kinetics of production of these chromatin fractions have been investigated. After a brief enzyme treatment (5 min at 10 enzyme units/A260 unit of chromatin at pH 6.6), 11% of the input chromatin DNA is found in the Mg2+ -soluble fraction. This DNA has a weight-average single-strand length of about 400 nucleotides and, as determined by renaturation kinetics, comprises a subset of nonrepetitive DNA sequences and a subset of families of middle repetitive sequences. This demonstrates the nonrandom distribution of repetitive and single copy sequences in the Mg2+ -soluble fraction of chromatin. Previous studies have shown that the Mg2+ -soluble fraction is enriched in nonrepeated sequences which are transcribed in vivo (Gottesfeld, J.M., Garrard, W.T., Bagi, G., Wilson, R.F., and Bonner, J. (1974), Proc. Natl. Acad. Sci. U.S.A. 71, 2193-2197). We now report that the Mg2+ -soluble fraction of liver chromatin contains a low proportion of sequences in common with the Mg2+ -soluble fraction of brain chromatin. Thus, fractionation does not depend on some general property of chromatin but is specific with regard to the template activity of the tissue from which the chromatin was obtained.     

Biochemical characteristics of the outer membranes of plant mitochondria

Like the outer membranes of liver mitochondria, those of plant mitochondria are impermeable to cytochrome c when intact and can be ruptured by osmotic shock. Isolated plant outer mitochondrial membranes are also similar to the corresponding liver membranes in terms of phospholipid and sterol content. Sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis experiments indicate that a single class of proteins (apparent molecular weight 30 000) comprises the bulk of the plant outer membrane protein. There are also considerable amounts of polysaccharide associated with these membranes, which may contribute to their osmotic stability.     

Protein migration into nuclei. I. Frog oocyte nuclei in vivo accumulate microinjected histones, allow entry to small proteins, and exclude large proteins

A technique is presented which enables one to measure the extent to which a protein enters and accumulates in the nucleus of the frog oocyte. In this method, the protein, labeled with 125-I, is microinjected into the oocyte. After incubation, the oocyte is manually enucleated and the radioactivity in the nucleus and cytoplasm is determined. Using this technique, proteins lighter than 20,000 daltons were found to enter the nucleus and completely equilibrate between the nucleus and cytoplasm within 24 h. The entry of proteins heavier than 69,000 daltons was severely hindered. Histones and histone fractions entered as quickly as other small proteins, but, in contrast to these proteins, they accumulated in the nucleus to different extents, depending on the total amount of histone injected into the oocyte and the identity of the histone. Evidence is presented that histone fractions compete with each other for accumulation in the nucleus.     

Determination of the active portion of the folic acid molecule in cellular slime mold chemotaxis.

From earlier work it is known that folic acid attracts the amoebae of various species of cellular slime molds (11). Here we have tested a wide variety of pteridines, pyrimidines, and pyrazines to determine what part of the folic acid molecule is chemotactically active. It was shown that the activity lies in the pteridine ring itself. Furthermore, the cell-free supernatants of slime mold amoebae contain an enzyme that renders pterin and folic acid chemotactically inactive, which apparently increases the chemotactic sensitivity of the amoebae to those compounds. Despite the fact that slime mold amoebae secrete small amounts of folic acid-related compounds, there is no evidence that folates are acrasins; rather it is postulated that attraction to folates may be a food-seeking device for the amoebae which prey on folate-secreting bacteria in the soil.     

On the origin of molecular “handedness” in living systems

Elementary particle effects (beta-decay) provide at best only a weakly handed radiation in the biologically effective energy ranges. Global magnetic effects coupled to sunlight are randomized by paleomagnetic reversals. Hence a persistent terrestrial handed bias at possible local biopoetic sites offers a more promising explanation for the origin of the "handedness" of the molecules found among living systems on earth. Magnetite in lava flows maintains a handed bias for surface catalysis through many magnetic reversals. Magnetite contaminated with sulfur has already been proposed by Granick as a biopoetic site because it provides a weak source of chemical energy derived by photochemical conversion. Indirect evidence for this hypothesis has been provided by the molecular structure of ferredoxin - a single strand of the 14 primordial amino acids wrapped around an FeS core. Lava flows have been suggested as biopoetic sites by Fox, since their temperature and chemical composition might allow for the rapid synthesis of prebiotic compounds at the surface of the primitive earth. The additional fact that magnetite in lave flows also provides a persistent handed site for surface catalysis offers a further argument for the experimental investigation of this specific biopoetic environment.     

质膜NAD(P)H氧化酶参予金瓜炭疽(Colletotrichum lagerarium)细胞壁激发子诱导人参细胞产生激发反应(英文)

在人参(Panax ginseng C.A.Meyer)悬浮细胞质膜上测出了NAD(P)H氧化酶活性。这类NAD(P)H氧化酶活性可以被金瓜炭疽细胞壁激发子(Cle)诱导。Cle处理还能诱导人参悬浮细胞的氧进发、促进人参悬浮细胞的皂苷合成、提高苯丙氨酸解氨酶(PAL)的活力、以及诱导查尔式酮酶(CHS)的累积和细胞壁上抗性相关蛋白基因脯氨酸富裕蛋白基因hrgp(Hydroxyprolin-rich glycoproleins)的表达。当用哺乳动物白细胞质膜NADPH氧化酶的特异性抑制剂二亚苯基碘(Diphenylene iodonium,DPI)与奎吖因(quinacrine)预处理人参悬浮细胞30 min 后,Cle诱导的H2O2释放与Cle激活的质膜NAD(P)H氧化酶活性被抑制,同时Cle诱导的PAL活性及CHS的积累下降,皂苷合成与hrgp的表达被抑制。由此推测:人参细胞质膜NAD(P)H氧化酶与哺乳动物白细胞质膜NADPH氧化酶有很大的相似性。在Cle激发人参悬浮细胞产生氧进发的过程中,NAD(P)H氧化酶活性被诱导从而导致H2O2的产生,H2O2作为第二信使,激活苯丙氨酸途径,诱发人参皂苷的合成及hrgp防御基因的表达。这一过程中还涉及到Ca2+内流,胞内Ca2+浓度的升高,蛋白磷酸化与去磷酸化。人参细胞质膜NAD(P)H氧化酶在人参细胞对Cle的反应过程中起一种介导作用。因此可能存在由Cle刺激,NAD(P)H氧化酶被诱导,H2O2释放,到人     

Genetic tailoring of N-linked oligosaccharides: the role of glucose residues in glycoprotein processing of Saccharomyces cerevisiae in vivo

In higher eukaryotes a quality control system monitoring the folding state of glycoproteins is located in the ER and is composed of the proteins calnexin, calreticulin, glucosidase II, and UDP-glucose: glycoprotein glucosyltransferase. It is believed that the innermost glucose residue of the N- linked oligosaccharide of a glycoprotein serves as a tag in this control system and therefore performs an important function in the protein folding pathway. To address this function, we constructed Saccharomyces cerevisiae strains which contain nonglucosylated (G0), monoglucosylated (G1), or diglucosylated (G2) glycoproteins in the ER and used these strains to study the role of glucose residues in the ER processing of glycoproteins. These alterations of the oligosaccharide structure did not result in a growth phenotype, but the induction of the unfolded protein response upon treatment with DTT was much higher in G0 and G2 strains as compared to wild-type and G1 strains. Our results provide in vivo evidence that the G1 oligosaccharide is an active oligosaccharide structure in the ER glycoprotein processing pathway of S.cerevisiae. Furthermore, by analyzing N- linked oligosaccharides of the constructed strains we can directly show that no general glycoprotein glucosyltransferase exists in S. cerevisiae.