Studies on the Biosynthesis of Vitamin B6

The production of vitamin B₆ (B₆) compounds with a cell-suspension of Achromobacter cycloclastes A.M.S. 6201 under various conditions were examined. An obvious accumulation of B₆ compounds in the incubation medium with a cell-suspension of the organism harvested at the middle to later part of exponential phase of growth was observed. γ-Aminobutyric acid or β-alanine was found to stimulate the B₆ production markedly, when they were added to the incubation mixture together with glycerol. Some discussion on the implication of these compounds as precursors of B₆ was presented.     

Biosynthesis of Vitamin B6 by a Yeast Mutant

The gradient-plate technique was employed to isolate mutants of Saccharomyces marxianus (NRRL-Y-1550) which, when grown in a synthetic culture medium, excreted about 2 mug/ml of vitamin B(6) as ascertained by microbiological assay. The major component that possessed vitamin B(6) activity was isolated by ion-exchange column chromatography and identified as pyridoxol by ultraviolet and fluorescence spectroscopy, as well as by paper chromatography and various chemical tests. Pyridoxal was also identified as one of the excreted compounds. Two other compounds that possessed vitamin B(6) activity were excreted in smaller quantities in the growth medium and have not yet been identified; they are not phosphates of vitamin B(6). The amount of vitamin B(6) excreted was not increased when the mutant was grown in the presence of various oxidation products of this vitamin. The methods and results reported here may be helpful in future studies on the biosynthesis of vitamin B(6).     

A Synthesis of Vitamin B6

In the presence of basic catalyst condensation of dehydrolevulinate and cyanoacetamide afforded ethyl 2-methyl-5-cyano-6-pyridone-4-carboxylate [IV]. Starting from [IV], a total synthesis of vitamin B₆ was described.     

Further Characterization of Glycolaldehyde Dehydrogenase Isozymes from Escherichia coli B Involvement in Vitamin B6 Biosynthesis

Kinetic study of glycolaldehyde dehydrogenase was performed with isozymes of Escherichia coli B. The reaction equilibrium of isozyme A was estimated to lie in glycolate formation, while those of isozymes B and C were in glycolaldehyde formation. Isozyme A was released from cells with osmotic shock, while the others were not. Isozymes B and C were found in cytoplasmic fraction. Some reversal mutants derived from WG3 strain (one of vitamin B₆ auxotrophs) acquired ability to produce isozyme C. Based on these results, the non-involvement of isozyme A in vitamin B₆ biosynthesis was discussed.     

Vitamin B6 Suppresses Growth of the Feline Mammary Tumor Cell Line FRM

Growth of FRM cells was inhibited by the addition of pyridoxine in a dose-dependent manner. Use of 5 mM pyridoxine caused an almost complete arrest of cell growth. Pyridoxal was as effective as pyridoxine, but pyridoxamine showed weak inhibitory action. Electron-microscopic examination of control cells revealed large nuclei and cellular membranes with villi, but, in pyridoxine-treated cells, condensed or degraded nuclei were observed. Many vacuoles and cholesterol crystals were widely distributed inside the cellular membrane of pyridoxine-treated cells. One of the vacuoles was identified as a lipid droplet. The DNA ladder was observed in the pyridoxine-treated cells. It is suggested that pyridoxine treatment of FRM cells causes cytolysis of cells by apoptosis.     

The Pseudoenzyme PDX1.2 Boosts Vitamin B6 Biosynthesis under Heat and Oxidative Stress in Arabidopsis

Vitamin B₆ is an indispensable compound for survival, well known as a cofactor for numerous central metabolic enzymes and more recently for playing a role in several stress responses, particularly in association with oxidative stress. Regulatory aspects for the use of the vitamin in these roles are not known. Here we show that certain plants carry a pseudoenzyme (PDX1.2), which is involved in regulating vitamin B₆ biosynthesis de novo under stress conditions. Specifically, we demonstrate that Arabidopsis PDX1.2 enhances the activity of its catalytic paralogs by forming a heterododecameric complex. PDX1.2 is strongly induced by heat as well as singlet oxygen stress, concomitant with an enhancement of vitamin B₆ production. Analysis of pdx1.2 knockdown lines demonstrates that boosting vitamin B₆ content is dependent on PDX1.2, revealing that this pseudoenzyme acts as a positive regulator of vitamin B₆ biosynthesis during such stress conditions in plants.     

维生素B12的生物合成、发酵生产与应用

维生素B12(VB12)是一种重要的动物和人类营养因子, 广泛应用于饲料、食品和医药卫生领域。中国已成为全球VB12的主要产地, 2007年产量为27 t, 占全球总产量的77%。VB12是目前已发现的最大、最复杂的维生素分子, 化学合成极其困难, 所有VB12产品均采用生物发酵制备其主体结构。VB12主要由古生菌和一些真细菌通过有氧或厌氧两种途径合成, 工业上主要采用费式丙酸菌(Propionibacterium freudenrechii）和脱氮假单胞菌(Pseudomonas denitrificans)进行发酵生产。综述了VB12的基本性质, 生物合成途径, 以及发酵生产工艺, 并对VB12的应用与市场前景作了分析。     

Biosynthesis of Vitamin B6 in Rhizobium: In Vitro Synthesis of Pyridoxine from 1-Deoxy-D-xylulose and 4-Hydroxy-L-threonine

Pyridoxine (vitamin B₆) in Rhizobium is synthesized from 1-deoxy-D-xylulose and 4-hydroxy-L-threonine. To define the pathway enzymatically, we established an enzyme reaction system with a crude enzyme solution of R. meliloti IFO14782. The enzyme reaction system required NAD⁺, NADP⁺, and ATP as coenzymes, and differed from the E. coli enzyme reaction system comprising PdxA and PdxJ proteins, which requires only NAD⁺ for formation of pyridoxine 5′-phosphate from 1-deoxy-D-xylulose 5-phosphate and 4-(phosphohydroxy)-L-threonine.     

A New Method for the Isolation of Etioplasts with Intact Envelopes

Electron micrographs are presented to demonstrate a new methodfor the isolation of etioplasts with intact envelopes developedafter comparing the known methods of isolation including thoseusing zonal centrifugation. This new method employs a columnof Sephadex G-50 (coarse) as one of the separation stages.     

Prebiotic Synthesis of Vitamin B6-type Compounds

Heating a dilute solution of NH3 and glycoaldehyde gives a large family of pyridines substituted with the same functional groups as occur in the forms of vitamin B6. Thus, vitamin B6-like molecules could have been present on the early Earth and could have been available for catalysis of primitive transamination reactions. Ethanolamine and N-methylethanolamine are also formed as major products. These are choline-like molecules, the latter of which is apparently formed by a prebiotic methylation process.     

Biosynthesis of vitamin B(6) in rhizobium

The biosynthetic pathway of pyridoxol (vitamin B(6)) in Rhizobium was clarified by studies on the incorporation of (13)C- or (15)N-labeled precursors into pyridoxol or its biosynthetic intermediates. Pyridoxol was formed by ring closure of two compounds, 1-deoxy-D-xylulose and 4-hydroxy-L-threonine. The former was formed from D-glyceraldehyde and pyruvate through decarboxylation of pyruvate, and the latter from glycine and glycolaldehyde.