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。     

乌索酸与齐墩果酸衍生物的合成进展

乌索酸和齐墩果酸在多种植物中均有分布.二者互为同分异构体,均属于五环三萜类化合物,由于其结构多样性而具有广泛的生物活性,包括抗肿瘤、抗氧化、抗艾滋病、抗溃疡、抗炎、免疫调节等功能.有关这两种活性物质的衍生化研究一直为科研人员所关注,本文主要综述了近10年来二者衍生物合成方面的新进展,为寻找活性先导化合物、合理设计药物分子提供依据.     

Biotransformation of Cinnamic Acid,p-Coumaric Acid,Caffeic Acid,and Ferulic Acid by Plant Cell Cultures of Eucalyptus perriniana

Biotransformations of phenylpropanoids such as cinnamic acid, p-coumaric acid, caffeic acid, and ferulic acid were investigated with plant-cultured cells of Eucalyptus perriniana. The plant-cultured cells of E. perriniana converted cinnamic acid into cinnamic acid β-D-glucopyranosyl ester, p-coumaric acid, and 4-O-β-D-glucopyranosylcoumaric acid. p-Coumaric acid was converted into 4-O-β-D-glucopyranosylcoumaric acid, p-coumaric acid β-D-glucopyranosyl ester, 4-O-β-D-glucopyranosylcoumaric acid β-D-glucopyranosyl ester, a new compound, caffeic acid, and 3-O-β-D-glucopyranosylcaffeic acid. On the other hand, incubation of caffeic acid with cultured E. perriniana cells gave 3-O-β-D-glucopyranosylcaffeic acid, 3-O-(6-O-β-D-glucopyranosyl)-β-D-glucopyranosylcaffeic acid, a new compound, 3-O-β-D-glucopyranosylcaffeic acid β-D-glucopyranosyl ester, 4-O-β-D-glucopyranosylcaffeic acid, 4-O-β-D-glucopyranosylcaffeic acid β-D-glucopyranosyl ester, ferulic acid, and 4-O-β-D-glucopyranosylferulic acid. 4-O-β-D-Glucopyranosylferulic acid, ferulic acid β-D-glucopyranosyl ester, and 4-O-β-D-glucopyranosylferulic acid β-D-glucopyranosyl ester were isolated from E. perriniana cells treated with ferulic acid.     

Enzymatic Formation of Hexadecenoic Acid from Palmitic Acid

Desaturation of palmitic acid was investigated in an enzyme system prepared from rat liver. 2-trans-Hexadecenoic acid as well as 9-cis-hexadecenoic acid (palmitoleic acid) were found to be formed as monoenoic acid in this system.     

Bacterial Degradation of 4-Hydroxyphenylacetic Acid and Homoprotocatechuic Acid

A species of Acinetobacter and two strains of Pseudomonas putida when grown with 4-hydroxyphenylacetic acid gave cell extracts that converted 3,4-dihydroxyphenylacetic acid (homoprotocatechuic acid) into carbon dioxide, pyruvate, and succinate. The sequence of enzyme-catalyzed steps was as follows: ring-fission by a 2,3-dioxygenase, nicotinamide adenine dinucleotide-dependent dehydrogenation, decarboxylation, hydration, aldol fission, and oxidation of succinic semialdehyde. Two new metabolites, 5-carboxymethyl-2-hydroxymuconic acid and 2-hydroxyhepta-2,4-diene-1,7-dioic acid, were isolated from reaction mixtures and a third, 4-hydroxy-2-ketopimelic acid, was shown to be cleaved by extracts to give pyruvate and succinic semialdehyde. Enzymes of this metabolic pathway were present in Acinetobacter grown with 4-hydroxyphenylacetic acid but were effectively absent when 3-hydroxyphenylacetic acid or phenylacetic acid served as sources of carbon.     

丙酮酸对细菌L-乳酸发酵的促进作用

研究了丙酮酸在不同浓度和添加时间对LactobacilluscaseiL 乳酸发酵过程中葡萄糖转化率和L 乳酸产量的影响。结果表明 ,当丙酮酸的添加量为 30g·L- 1 时 ,L 乳酸的产量达到 74g·L- 1 。在 72h的发酵周期内 ,丙酮酸在 2 4h和 42h添加的效果好于其他时间添加。     

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.     

Abscisic Acid ELISA: Organic Acid Interference

Consideration must be exercised in determination of buffers and solutions used when carrying out enzyme-linked immunosorbent assays (ELISAs). A commercial monoclonal antibody kit for abscisic acid (Idetek, Inc.) gives significant false-positives with tricarboxylic acid cycle intermediates. The organic acids or contaminants interfered with ELISA assays for ABA as indicated by deviations in the slopes of standard curves of ABA in the organic acids. The interference, in the case of α-ketoglutarate, was caused by a contaminant. Of the organic buffers tested—Tris, Tricine, and Hepes—only Hepes showed false-positive ABA. In addition, we present data indicating the presence of ABA in commercial mannitol and provide a simple procedure for removal of the ABA.     

Turnover of Free Sialic Acid, CMP-Sialic Acid, and Bound Sialic Acid In Rat Brain

Abstract: Adult male rats were injected intraventricularly with N-[³H]acetylmannosamine. After different time intervals the rats were killed and free sialic acid, CMP-sialic acid, lipid- and protein-bound sialic acid were isolated from brain and the specific radioactivities determined. Maximal specific radioactivity was reached after approximately 4 h for CMP-sialic acid, after 10–12 h for free sialic acid and after approximately 42 h for lipid-and protein-bound sialic acid. After some days the specific radioactivities of all four pools were the same and decreased equally, with a calculated turnover rate of approximately 3.5 weeks. The conclusion was that this phenomenon was the result of reutilisation of sialic acid and/or precursors. Therefore, the calculated turnover is not the turnover of bound sialic acid, but merely the rate of leakage of sialic acid and/or precursors out of the brain, so that no real turnover can be measured by this method. The first few hours after injection the specific radioactivity of CMP-sialic acid rose above that of free sialic acid. It is supposed that a compartmentalization exists of free sialic acid. The newly synthesized sialic acid molecules are not secreted into the cytoplasmic pool but are preferentially used for the synthesis of CMP-sialic acid. The results and conclusions are discussed in view of the general problems concerning turnover measurements of glycoconjugates.     

以L-天冬氨酸为原料制备D-天冬氨酸的新方法

以L-天冬氨酸为原料经过酯化、消旋、拆分和水解制备D-天冬氨酸。使L-2,3-二苯甲酰酒石酸(L-DBTA)与DL-天冬氨酸-β-甲酯在水溶液中于65~70℃反应形成非对映体盐,冷却到室温,D-天冬氨酸.L-DBTA盐析出,过滤后再经水解得到D-天冬氨酸,收率78.2%,旋光纯度达到99%以上。     

Purification and Characterization of the Heat-Stable Factors Essential for the Conversion of Lignoceric Acid to Cerebronic Acid and Glutamic Acid: Identification of N-Acetyl-l-Aspartic Acid

Abstract: The conversion of lignoceric acid to cerebronic acid, ceramides, cerebrosides, and glutamic acid is catalyzed by a rat brain particulate preparation. The heat-stable factor, prepared from calf cerebellum, together with the heat-labile factor, a pyridine nucleotide, and Mg²⁺ are essential to all of these metabolic pathways. Our previous work showed that the heat-stable factor is composed of at least two components, HSF-1 and HSF-2, and identified HSF-2 as d -glucose-6-phosphate. In the current investigation, HSF-1 was further purified and found to be N -acetyl- l -aspartic acid. In addition, it was discovered that a third component, HSF-3, is also required for heat-stable factor activity. A reconstituted system composed of N -acetylaspartic acid, glucose-6-phosphate, and HSF-3 fully replaced the heat-stable factor essential for the conversion of lignoceric acid to cerebronic acid and glutamic acid. The reconstituted heat-stable factor did not show the initial time lag always observed with the crude heat-stable factor.     

The Selective Effect of Abscisic Acid on Ribonucleic Acid Components

As determined by methylated albumin kieselguhr (MAK) fractionation, GA₃ (gibberellic acid) significantly increased and ABA (abscisic acid) decreased RNA levels. In the case of ABA this effect was selective, the ribosomal RNA manifesting the typical decrease; while the sRNA peak was markedly increased. The pattern of labelled uridine incorporation into RNA resembles the MAK absorbancy profile and here as well, ABA although causing an overall decrease, increases labelling in the sRNA peak. The results are interpreted as a possible selective effect of ABA or alternatively as an accumulation in the sRNA peak of rRNA breakdown products. From in vitro experiments it was furthermore evident that ABA mediated RNA hydrolysis probably does not involve a direct activation of RNase by ABA. The in vivo effect would probably be devious.     

Hyaluronic Acid Degradation by Ascorbic Acid and Influence of Iron

The effects of ascorbic acid, iron and ADP on hyaluronic acid, a compound present in inflamed joints, were investigated in an in vitro system. Ascorbic acid induces degradation of hyaluronic acid which increased in the presence of FeCl, and which is additionally stimulated by ADP chelated ferric ions. The hyaluronic acid degrading reactions induced by the Fe-III/ADP/ascorbic acid system were inhibited by catalase and formate to various extents whereas the presence of superoxide dismutase did not exert any inhibitory effect. Desferrioxamine, a specific iron chelator, completely inhibited hyaluronic acid depolymerisation by ascorbic acid as well as in combination with FeCl₃ or FeCl₃/ADP, respectively. We suggest that the ultimate hyaluronic acid degrading species is OH', generated via the Fe-III/ADP catalysed Haber Weiss reaction. There is also an indication for the involvement of perferryl or/and ferryl species in the degradation process.     

Hyaluronic Acid Degradation by Ascorbic Acid and Influence of Iron

The effects of ascorbic acid, iron and ADP on hyaluronic acid, a compound present in inflamed joints, were investigated in an in vitro system. Ascorbic acid induces degradation of hyaluronic acid which increased in the presence of FeCl, and which is additionally stimulated by ADP chelated ferric ions. The hyaluronic acid degrading reactions induced by the Fe-III/ADP/ascorbic acid system were inhibited by catalase and formate to various extents whereas the presence of superoxide dismutase did not exert any inhibitory effect. Desferrioxamine, a specific iron chelator, completely inhibited hyaluronic acid depolymerisation by ascorbic acid as well as in combination with FeCl₃ or FeCl₃/ADP, respectively. We suggest that the ultimate hyaluronic acid degrading species is OH', generated via the Fe-III/ADP catalysed Haber Weiss reaction. There is also an indication for the involvement of perferryl or/and ferryl species in the degradation process.     

Inactivation of Enzymes by Linoleic Acid Hydroperoxides and Linoleic Acid

The inactivation of the enzymes by linoleic acid hydroperoxides (LAHPO) was tested in connection with the toxicity of oxidized fat. At the same time, the inhibition of enzyme activities by linoleic acid was also tested. Ribonuclease (RNase), trypsin, chymotrypsin and pepsin which are considered to be simple proteins and not to be SH-enzymes were chosen as the enzymes. RNase was largely inhibited by LAHPO, but the other enzymes were inhibited by linoleic acid as well as LAHPO. The inhibition of each enzyme occurred at different pH. This fact may show that the inhibition occurs by binding of such hydrophobic compounds to the enzyme, and that the surface exposition of hydrophobic region may depend on the pH. Not only the reaction of some specific amino acid residue in the protein molecules with LAHPO, but also the binding of these hydrophobic compounds must be remembered in the mechanism of inhibition.     

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.