转化酶在高等植物蔗糖代谢中的作用研究进展

蔗糖转化酶在高等植物蔗糖代谢中起着关键的作用。研究表明,转化酶参与植物的生长、器官建成、糖分运输、韧皮部卸载及调节库组织糖分构成及水平。近年来关于该酶的生化特性、基因表达与调控以及结构与功能等的研究取得了重要进展。本文介绍了转化酶在植物体内的种类、分布、分子结构特点、生理作用及分子生物学研究进展。     

转化酶在高等植物蔗糖代谢中的作用研究进展

蔗糖转化酶在高等植物蔗糖代谢中起着关键的作用。研究表明 ,转化酶参与植物的生长、器官建成、糖分运输、韧皮部卸载及调节库组织糖分构成及水平。近年来关于该酶的生化特性、基因表达与调控以及结构与功能等的研究取得了重要进展。本文介绍了转化酶在植物体内的种类、分布、分子结构特点、生理作用及分子生物学研究进展。     

Studies in the Respiratory and Carbohydrate Metabolism of Plant Tissues2

Feeding strawberry and poplar leaves with iodoacetate, arsenite,or fluoride decreased the contents of sucrose and ascorbate.The content of hexose increased in high concentrations of iodoacetatebut decreased in moderate strengths. Iodo-acetate increasedthe rate of CO₂ output and caused a large decrease in phospholipidwith increase of inorganic phosphate. When iodoacetate was fedin nitrogen, CO₂ output did not increase. An explanation of the results is that the sucrose and ascorbateof the cell are mainly confined to the vacuole and that theabove poisons accelerate the leakage of these compounds fromthe vacuole so that they are metabolized more rapidly in thecytoplasm. An additional possibility is that iodoacetate ‘uncouples’oxidative phosphorylation, thereby stimulating respiration andmore rapid metabolism of both sucrose and ascorbate.     

Studies in the Respiratory and Carbohydrate Metabolism of Plant Tissues1

Oxygen at pressures of 2 and 3 atmospheres caused an initialincrease in CO₂ output of strawberry leaves followed by a decrease.In oxygen at 2 atmospheres, but not in oxygen at 3 atmospheres,the increase in CO₂ output could be attributed to an increasein glucose-6-phosphate and in fructose diphosphate; in oxygenat 3 atmospheres the increase may be due to an increased accessibilityof substrates and enzymes or to other causes. The decline inCO₂ output in oxygen at both 2 and 3 atmospheres was associatedwith large decreases in glucose-6-phosphate and 3-phosphoglycerate,probably due to a large decrease in adenosine triphosphate relatedto a ‘block’ of the tricarboxylic acid cycle.     

Focus on Metabolism: Posttranslational Protein Modifications in Plant Metabolism

Posttranslational modifications (PTMs) of proteins greatly expand proteome diversity, increase functionality, and allow for rapid responses, all at relatively low costs for the cell. PTMs play key roles in plants through their impact on signaling, gene expression, protein stability and interactions, and enzyme kinetics. Following a brief discussion of the experimental and bioinformatics challenges of PTM identification, localization, and quantification (occupancy), a concise overview is provided of the major PTMs and their (potential) functional consequences in plants, with emphasis on plant metabolism. Classic examples that illustrate the regulation of plant metabolic enzymes and pathways by PTMs and their cross talk are summarized. Recent large-scale proteomics studies mapped many PTMs to a wide range of metabolic functions. Unraveling of the PTM code, i.e. a predictive understanding of the (combinatorial) consequences of PTMs, is needed to convert this growing wealth of data into an understanding of plant metabolic regulation.The primary amino acid sequence of proteins is defined by the translated mRNA, often followed by N- or C-terminal cleavages for preprocessing, maturation, and/or activation. Proteins can undergo further reversible or irreversible posttranslational modifications (PTMs) of specific amino acid residues. Proteins are directly responsible for the production of plant metabolites because they act as enzymes or as regulators of enzymes. Ultimately, most proteins in a plant cell can affect plant metabolism (e.g. through effects on plant gene expression, cell fate and development, structural support, transport, etc.). Many metabolic enzymes and their regulators undergo a variety of PTMs, possibly resulting in changes in oligomeric state, stabilization/degradation, and (de)activation (Huber and Hardin, 2004), and PTMs can facilitate the optimization of metabolic flux. However, the direct in vivo consequence of a PTM on a metabolic enzyme or pathway is frequently not very clear, in part because it requires measurements of input and output of the reactions, including flux through the enzyme or pathway. This Update will start out with a short overview on the major PTMs observed for each amino acid residue (PTMs, including determination of the localization within proteins (i.e. the specific residues) and occupancy. Challenges in dealing with multiple PTMs per protein and cross talk between PTMs will be briefly outlined. We then describe the major physiological PTMs observed in plants as well as PTMs that are nonenzymatically induced during sample preparation (PTMs, in particular for enzymes in primary metabolism (Calvin cycle, glycolysis, and respiration) and the C4 shuttle accommodating photosynthesis in C4 plants (PTMs observed in plants

Studies on the Metabolism of Aspergilli

Studies were made on the effect of water level of culture medium on the mycelial compositions and enzyme production in Aspergillus sojae K. S. The mold was grown on the media of various water levels made of powder of defatted soybean and wheat granule. The mycelia grown on the medium of low water level produced more protease and α-amylase, consumed more oxygen, formed less ammonia, and were richer in 2 n H₂SO₄-soluble glycogen, 60% H₂SO₄-soluble carbohydrates, protein and RNA per mg dry weight than the mycelia grown on the medium of high water level. Chromatographic analyses were carried out for nucleotides, sugar phosphates and free carbohydrates in cold TCA-soluble fraction of the mycelia.     

Studies on the Metabolism of Aspergilli

This report is concerned with the time course of changes of several enzymes during endogenous respiration. It was observed that enzymes such as deaminases, amidases and transaminases found in the mycelia increased in activity more or less during endogenous respiration. It was assumed that enzyme formation occurred as the result of glucose starvation or depression of carbohydrate metabolism during endogenous respiration of the mold mycelia on buffer solution.     

Studies on the Metabolism of Aspergilli

Studies were made on the endogenous respiration of Aspergillus sojae K.S. Observing the changes of Kjeldahl-nitrogen in each fraction of the mycelial components, the author concluded that pool amino acids, bound amino acids, protein, nucleic acids and nucleotides covered whole of the nitrogenous reserves available for endogenous respiration in the mycelia. A study was carried out on the effect of preincubation with glucose or amino acids on endogenous respiration. Stimulation of either oxygen uptake, protein breakdown or ammonia formation was observed during respiration of the mycelia incubated with a suitable concentration of azide, 2,4-dinitrophenol, potossium fluoride, monoiodoacetic acid or ethylenediaminetetraacetic acid. Ammonia formation accompanied with endogenous respiration seemed to proceed inversely by the influence of energy yielding reaction.     

Studies on the Metabolism of Aspergillii

Endogenous respiration of Aspergillus sojae K.S. was studied in terms of biochemical analysis. It was found that the different kind of substrates was utilized for the endogenous respiratoin according to C:N ratio of the agar medium on which the mold was grown. In the mycelial mats grown on the medium of low C:N value, pool amino acids, protein, and nucleic acids were mainly utilized from the beginning while carbohydrate or lipid displayed a minor role. The corresponding amount of ammonia was formed. On the other hand, in the mycelial mats grown on the medium of rather high C:N value, carbohydrate or lipid was the major substrate of endogenous respiration in the early stages of incubation. The utilization of the nitrogenous materials and the accompanying formation of ammonia got to start only after the lapse of several hours of incubation.     

Studies on the Metabolism of Aspergilli

It was found that either γ-glutamic hydrazide or hydrazine at an appropriate concentration stimulated the formation of glutamic dehydrogenase as well as transaminases. Addition of l-glutamine partially reduced the stimulating effects of analogues.     

植物次生代谢基因工程

植物次生代谢基因工程,是利用基因工程技术对植物次生代谢途径的遗传特性进行改造,进而改变植物次生代谢产物。植物次生代谢基因工程的出现是人类对次生代谢途径的深入了解和分子生物学向纵深发展的结果,同时它又促进了次生代谢分子生物学的发展。调控因子的应用和多基因的协同转化为植物次生代谢基因工程拓宽了思路。从次生代谢图谱、植物基因工程策略和植物转基因方法等方面对植物次生代谢的基因工程研究进展做一简要概述。