Role of Ribonucleic Acid Synthesis in Replication of Deoxyribonucleic Acid

An experiment previously interpreted to show a ribonucleic acid requirement for propagation of deoxyribonucleic replication is reexamined and the earlier interpretation is shown to be incorrect.     

Synthesis of l-(+)-Tartaric Acid from l-Ascorbic Acid via 5-Keto-d-Gluconic Acid in Grapes

5-Keto-l-idionic acid (5-keto-d-gluconic acid, d-xylo-5-hexulosonic acid) was found as a metabolic product of l-ascorbic acid in slices of immature grapes, Vitis labrusca L. cv `Delaware'. Specifically labeled compounds, recognized as metabolic products of l-ascorbic acid in grapes, were fed to young grape tissues to investigate the metabolic pathway from l-ascorbic acid to l-(+)-tartaric acid.     

Structures of Hexadecenoic Acid and Octadecenoic Acid in Lipomyces starkeyi

Taxonomic and some other properties of a yeast strain, Candida sp. 36, which characteristically assimilates n-alkanes, were described. Identification of coenzyme Q, NMR spectroscopy of cell wall polysaccharides, determination of G+C content of DNA and some DNA-DNA hybridization experiments were carried out, in addition to the morphological and physiological observations. All the data were consistent with the suggestion that Candida cloacae Komagata, Nakase and Katsuya and Candida subtropicalis Nakase, Fukazawa and Tsuchiya are the synonyms of Candida maltosa Komagata, Nakase and Katsuya. Candida sp. 36 was identified as C. maltosa, too. The yeast was found to grow most abundantly on n-hexadecane and on n-octadecane in the presence of biotin.     

Role of Acetohydroxy Acid Isomeroreductase in Biosynthesis of Pantothenic Acid in Salmonella typhimurium

Structural genes have been identified for all of the enzymes involved in the biosynthesis of pantothenic acid in Salmonella typhimurium and Escherichia coli K-12, with the exception of ketopantoic acid reductase, which catalyzes the conversion of α-ketopantoate to pantoate. The acetohydroxy acid isomeroreductase from S. typhimurium efficiently bound α-ketopantoate (K_m = 0.25 mM) and catalyzed its reduction at 1/20 the rate at which α-acetolactate was reduced. Since two enzymes could apparently participate in the synthesis of pantoate, a S. typhimurium ilvC8 strain was mutagenized to derive strains completely blocked in the conversion of α-ketopantoate to pantoate. Several isolates were obtained that grew in isoleucine-valine medium supplemented with either pantoate or pantothenate, but not in the same medium supplemented with α-ketopantoate or β-alanine. The mutations that conferred pantoate auxotrophy (designated panE) to these isolates appeared to be clustered, but were not linked to panB or panC. All panE strains tested had greatly reduced levels of ketopantoic acid reductase (3 to 12% of the activity present in DU201). The capacity of the isomeroreductase to synthesize pantoate in vivo was assessed by determining the growth requirements of ilvC⁺ derivatives of panE ilvC8 strains. These strains required either α-ketopantoate, pantoate, or pantothenate when the isomeroreductase was present at low levels; when the synthesis of isomeroreductase was induced, panE ilvC⁺ strains grew in unsupplemented medium. These phenotypes indicate that a high level of isomeroreductase is sufficient for the synthesis of pantoate. panE ilvC⁺ strains also grew in medium supplemented with lysine and methionine. This phenotype resembles that of some S. typhimurium ilvG mutants (e.g., DU501) which are partially blocked in the biosynthesis of coenzyme A and are limited for succinyl coenzyme A. panE ilvC⁺ strains which lack the acetohydroxy acid synthases required only methionine for growth (in the presence of leucine, isoleucine, and valine). This and other evidence suggested that the synthesis of pantoic acid by isomeroreductase was blocked by the α-acetohydroxy acids and that pantoic acid synthesis was enhanced in the absence of these intermediates, even when the isomeroreductase was at low levels. panE ilvC⁺ strains reverted to pantothenate independence. Several of these revertants were shown to have elevated isomeroreductase levels under noninduced and induced conditions; the suppressing mutation in each revertant was shown to be closely linked to ilvC by P22 transduction. This procedure presents a means for obtaining mutants with altered regulation of isomeroreductase.     

Metabolic Conversion of l-Ascorbic Acid to Oxalic Acid in Oxalate-accumulating Plants

l-Ascorbic acid-1-(14)C and its oxidation product, dehydro-l-ascorbic acid, produced labeled oxalic acid in oxalate-accumulating plants such as spinach seedlings (Spinacia oleracea) and the detached leaves of woodsorrel (Oxalis stricta and O. oregana), shamrock (Oxalis adenopylla), and begonia (Begonia evansiana). In O. oregana, conversion occurred equally well in the presence or absence of light. This relationship between l-ascorbic acid metabolism and oxalic acid formation must be given careful consideration in attempts to explain oxalic accumulation in plants.     

Fatty Acid Replacements in a Fatty Acid Auxotroph of Escherichia coli

Unsaturated fatty acids having structural features which are different from those of the monoenoic acids normally synthesized by Escherichia coli can serve as growth factors for an auxotroph requiring unsaturated fatty acids. These analogues were incorporated into the phospholipids, as shown by gas-liquid and thin-layer chromatographic analysis of the phospholipid fatty acid composition. Some of these fatty acids were cisDelta(5)- and cis-Delta(9)-tetradecenoic, cis-Delta(11)-eicosenoic, cis,cis-Delta(11,14)-eicosadienoic, cis,cis,cis-Delta(11,14,17)-eicosatrienoic, trans-Delta(9)- and trans-Delta(11)-octadecenoic acids. Although partial degradation of some of these analogues to shorter even-chain homologues occurred, chain elongation of the exogenous fatty acids was not detected. Trans-olefinic acids were utilized without stereochemical or positional isomerization. These studies provide a basis for exploring the properties of the fatty acids and phospholipids required for the formation, structure, and function of membranes.     

Inhibition of Ribonucleic Acid Synthesis by Nalidixic Acid in Escherichia coli

The effect of low concentrations of nalidixic acid on ribonucleic acid (RNA) synthesis in Escherichia coli was examined. It was observed that RNA synthesis in exponentially growing cells was not significantly affected, in harmony with previous studies. However, RNA synthesis was markedly depressed by nalidixic acid during starvation for an amino acid or during chloramphenicol treatment. This effect was not caused by increased killing or inhibition of nucleoside triphosphate synthesis by nalidixic acid. The pattern of radioactive uracil incorporation into transfer RNA or ribosomes was not changed by the drug. The sensitivity of RNA synthesis to nalidixic acid in the absence of protein production may be useful in probing the amino acid control of RNA synthesis.     

氨基酸分析仪测定饲料添加剂——叶酸的方法

用６ｍｏｌ／Ｌ盐酸于１１０℃条件下水解饲料添加剂——叶酸,使之游离出谷氨酸,用氢氧化钠中和调节ｐＨ到２,氨基酸分析仪测定谷氨酸含量,经与标准叶酸水解样品比较,计算出叶酸的纯度。该方法重现性好,变异系数ＣＶ＝０．０８％,平均回收率为９８．３４％,浓度与峰面积呈线性相关,相关系数ｒ＝０．９９８７,可随氨基酸分析同时进行,不需改变任何分析条件。     

The Hazard of Acid Differentiation in Gomori's Method for Acid Phosphatase

In his original method for the histochemical demonstration of acid phosphatase, Gomori prescribed differentiation of incubated sections by rinsing them in 14% aqueous acetic acid, to remove the nonspecifically precipitated lead deposits. According to him, the enzymatically produced lead phosphate is not washed out by this procedure. As a result of recent improvements in tissue preparation and shorter incubation time, this staining reaction as it is used now is quite sensitive to an acetic acid wash. If this wash is used as recommended originally, it may completely abolish a truly positive reaction. To avoid falsely negative results, and to compare sections of normal and pathological tissue, omission of this differentiation by acetic acid is essential. The risk of mistaking nonspecific lead precipitates in the interpretation of a positive reaction is very small, and can be avoided by running a negative control slide in which no lead phosphate can be produced enzymatically.     

Ultraviolet-Induced Cross-Links in the Deoxyribonucleic Acid of Single-Stranded Deoxyribonucleic Acid Viruses as a Probe of Deoxyribonucleic Acid Packaging

Deoxyribonucleic acid (DNA) from ultraviolet (UV)-irradiated phiX174 sediments in alkali at rates up to 1.7 times that of unirradiated phiX174 DNA and is observed as a condensed, cross-linked structure when examined in the electron microscope by the formamide spreading technique. This structure appears to result from multiple cross-links induced in the tightly coiled DNA contained within the spherical phiX174 capsid. In contrast, the DNA extracted after UV irradiation of the filamentous bacteriophage M13 is not strikingly altered in its sedimentation properties and appears by electron microscopy to be rod-shaped as a result of side-to-side association of the circular DNA. The differences in these UV-induced structures reflect the differences in the packaging of the single-stranded DNA in the two virions.     

Interactions of indoleacetic Acid and gibberellic Acid in leaf abscission control

Debladed midribs of citrus leaves showed the typical delay of abscission in response to indoleacetic acid (IAA), and the typical acceleration of abscission in response to gibberellic acid (GA). Interaction experiments with these 2 hormones indicated that the balance of the 2 hormones may be more important in regulating abscission than the quantity of either. The often reported acceleration of abscission with low quantities of IAA did not seem to exist in citrus. IAA did accelerate abscission in this tissue when its application was delayed for at least 24 hours after deblading, which suggests the 2-stage effect is also present in citrus.

When abscission was first delayed with IAA and then allowed to continue, the rate of abscission proceeded at a slower rate than was typical for this tissue. This slower rate was also typical of the effect observed when GA overcame the abscission retarding effect of IAA. The phenylurethane, Barban, blocked the GA acceleration of abscission, but it did not affect the rate of abscission of control or IAA treated midribs.

     

Characterization of Excess Deoxyribonucleic Acid Synthesized by Pneumococci in the Presence of Polyadenylic Acid and Deoxyribonucleic Acid Precursors

Excess deoxyribonucleic acid (DNA) synthesized by cell suspensions of encapsulated pneumococci in the presence of polyadenylic acid plus all eight of the naturally occurring deoxyribonucleosides and deoxyribonucleotides has been characterized in several ways. The DNA represents complete molecules, is synthesized by a relatively large population at a steady rate, and is replicated in a semiconservative manner.     

Endogenous levels of abscisic Acid and decanoic Acid in dutch iris bulbs and the influence of abscisic Acid and decanoic Acid on iris meristems cultured in vitro

Abscisic acid (ABA) and decanoic acid inhibited shoot elongation and floral development of Dutch iris (Iris hollandica Hoog. cv Ideal) meristems cultured in vitro. No synergism with respect to inhibition of leaf growth between ABA and decanoic acid was observed. With monthly harvest dates, from July 10, 1981 to October 10, 1981, there was a progressive decrease in endogenous level of free ABA in `Ideal' iris bulbs. Bulbs subjected to a full set of the usual preplanting storage conditions flowered, on average, 46 days after planting versus 194 days after planting for bulbs planted directly after harvest. ABA levels at harvest were 4- to 5-fold those after the preplanting storage treatment. In general, ABA levels did not correlate well with the length of time from planting until flowering of iris bulbs. Endogenous decanoic acid levels did not follow any pattern with respect to harvest date or postharvest treatment. After the postharvest high temperature treatment, there was about a 3-fold increase in nonscale decanoic acid concentration. Decanoic acid levels, in nonscale tissue, remained high after each of the other postharvest treatments. It is concluded that there is no good evidence to support the contention that either ABA or decanoic acid is directly involved in iris bulb dormancy.     

乳酸菌酸胁迫反应机制研究进展

乳酸菌可发酵糖类产生乳酸,并广泛应用于食品、药物和饲料等工业。由于有机酸的积累,乳酸菌大部分的生长代谢都在低pH的酸性环境中进行,具有酸胁迫反应。pH的自我平衡、ATR反应机制、对大分子的保护和修复作用及细胞膜的变化等是乳酸菌酸胁迫反应的主要机制,其中,pH自我平衡包括F0F1-ATPase质子泵、精氨酸脱氨酶途径(ADI)和谷氨酸脱羧酶途径(GAD)等。由此可见,乳酸菌酸胁迫反应机制涉及到基因和蛋白的表达调控等,是非常复杂的网络调控体系。