保加利亚乳杆菌生长性能与后酸化的关系初探

以5株德氏乳杆菌保加利亚亚种为出发菌株,详细研究了5株菌的生长代谢、酸敏感性及蛋白水解力,并分析了这些特性与后酸化之间的关系。结果表明:5株菌的生长性能与后酸化之间存在紧密联系。其中,菌株的生长速度和糖分解代谢能力与后酸化成正比;对酸较敏感菌株的后酸化也较弱;菌株的蛋白水解能力与生长速度和后酸化之间没有明显的相关性。     

In Vivo Metabolic Responses to Different Formulations of Amino Acid Mixtures for the Treatment of Phenylketonuria (PKU)

Phenylketonuria (PKU) is a rare autosomal recessive inborn error of metabolism where the mainstay of treatment is a Phe restricted diet consisting of a combination of limited amounts of natural protein with supplementation of Phe-free or low-Phe protein substitutes and special low protein foods. Suboptimal outcomes may be related to the different absorption kinetics of free AAs, which have lower biological efficacy than natural proteins. Physiomimic Technology^TM is a technology engineered to prolong AA (AA-PT) release allowing physiological absorption and masking the odor and taste of free AAs. The aim of these studies was to assess the impact of AA-PT formulation on selected functional and metabolic parameters both in acute and long-term experimental studies. Adult rats in fasting conditions were randomized in different groups and treated by oral gavage. Acute AA-PT administration resulted in significantly lower BUN at 90 min versus baseline. Both BUN and glycemia were modulated in the same direction as intact casein protein. Long-term treatment with AA-PT significantly reduces the protein expression of the muscle degradation marker Bnip3L (−46%) while significantly increasing the proliferation of market myostatin (+58%). Animals dosed for 15 days with AA-PT had significantly stronger grip strength (+30%) versus baseline. In conclusion, the results suggest that the AA-PT formulation may have beneficial effects on both AA oxidation and catabolism with a direct impact on muscle as well as on other metabolic pathways.     

Metabolic costs of terpenoid accumulation in higher plants

The net value of any plant trait can be assessed by measuring the costs and benefits associated with that trait. While the other contributors to this issue examine the possible benefits of terpenoids to plants, this article explores the metabolic costs of terpenoid accumulation in plants in the light of recent advances in terpenoid biochemistry. Terpenoids are more expensive to manufacture per gram than most other primary and secondary metabolites due to their extensive chemical reduction. The enzyme costs of making terpenoids are also high since terpenoid biosynthetic enzymes are apparently not shared with other metabolic pathways. In fact, plant cells may even possess more than one set of enzymes for catalyzing the basic steps of terpenoid formation. Terpenoids are usually sequestered in complex, multicellular secretory structures, and so storage costs for these substances are also likely to be substantial. However, not all of the processes involved in terpenoid accumulation require large investments of resources. For instance, the maintenance of terpenoid pools is probably inexpensive because there is no evidence that substantial quantities of terpenes are lost as a result of metabolic turnover, volatilization, or leaching. Moreover, plants may reduce their net terpenoid costs by employing individual compounds in more than one role or by catabolizing substances that are no longer needed, although it is still unclear if such practices are widespread. These findings (and other facets of terpenoid biochemistry and physiology) are discussed in relation to the assumptions and predictions of several current theories of plant defense, including the carbonnutrient balance hypothesis, the growth-differentiation balance hypothesis, and the resource availability hypothesis.     

Energy Catabolism in Rabbit Muscle as Affected by Brine Injection: 31P NMR Studies

The energy catabolism in brine-injected muscles was examined by ³¹P Nuclear Magnetic Resonance (NMR) spectroscopy. Immediately after death of rabbits, brines containing NaCl, with or without pyrophosphate, were injected into the arterial system. ³¹P NMR spectra at 4°revealed marked heterogeneity in postmortem catabolism due to brine diffusion. The heterogeneity of the Pi signal for injected muscles reflected the existence of muscle areas with different intracellular pH values. This observation suggested an increase in rate of glycolysis for fibers experiencing brine. The heterogeneity of brine diffusion seemed to be affected by method of injection.     

烟碱的微生物代谢研究进展

综述了代谢烟碱微生物的种类、微生物代谢烟碱的途径、分子生物学机理和酶学研究及微生物代谢烟碱应用研究的进展情况,揭示出微生物在降低烟草和环境中烟碱含量的潜力.     

Bacterial Catabolism of Biphenyls: Synthesis and Evaluation of Analogues

A series of alkylated 2,3‐dihydroxybiphenyls has been prepared on the gram scale by using an effective Directed ortho Metalation–Suzuki–Miyaura cross‐coupling strategy. These compounds have been used to investigate the substrate specificity of the meta‐cleavage dioxygenase BphC, a key enzyme in the microbial catabolism of biphenyl. Isolation and characterization of the meta‐cleavage products will allow further study of related processes, including the catabolism of lignin‐derived biphenyls.     

Peptide and protein drugs: the study of their metabolism and catabolism by mass spectrometry

Peptide and protein drugs have evolved in recent years into mainstream therapeutics, representing a significant portion of the pharmaceutical market. Peptides and proteins exhibit highly diverse structures, broad biological activities as hormones, neurotransmitters, structural proteins, metabolic modulators and therefore have a significant role as both therapeutics and biomarkers. Understanding the metabolism of synthetic or biotechnologically derived peptide and protein drugs is critical for pharmaceutical development as metabolism has a significant impact on drug efficacy and safety. Although the same principles of pharmacokinetics and metabolism of small molecule drugs apply to peptide and protein drugs, there are few notable differences. Moreover, the study of peptide and protein drug metabolism is a rather complicated process which requires sophisticated analytical techniques, and mass spectrometry based approaches have provided the capabilities for efficient and reliable quantification, characterization, and metabolite identification. This review article will focus on the current use of mass spectrometry for the study of the metabolism of peptide and protein drugs.     

Identification of Correlative Shifts in Indices of Brain Cholesterol Metabolism in the C57BL6/Mecp2tm1.1Bird Mouse,a Model for Rett Syndrome

Rett syndrome (RS) is a pervasive neurodevelopmental disorder resulting from loss‐of‐function mutations in the X‐linked gene methyl‐Cpg‐binding protein 2 (MECP2). Using a well‐defined model for RS, the C57BL6/Mecp2^tm1.1Bird mouse, we have previously found a moderate but persistently lower rate of cholesterol synthesis, measured in vivo, in the brains of Mecp2^?/y mice, starting from about the third week after birth. There was no genotypic difference in the total cholesterol concentration throughout the brain at any age. This raised the question of whether the lower rate of cholesterol synthesis in the mutants was balanced by a fall in the rate at which cholesterol was converted via cholesterol 24‐hydroxylase (Cyp46A1) to 24S‐hydroxycholesterol (24S‐OHC), the principal route through which cholesterol is ordinarily removed from the brain. Here, we show that while there were no genotypic differences in the concentrations in plasma and liver of three cholesterol precursors (lanosterol, lathosterol, and desmosterol), two plant sterols (sitosterol and campesterol), and two oxysterols (27‐hydroxycholesterol [27‐OHC] and 24S‐OHC), the brains of the Mecp2 ^?/y mice had significantly lower concentrations of all three cholesterol precursors, campesterol, and both oxysterols, with the level of 24S‐OHC being ~20% less than in their Mecp2 ^+/y controls. Together, these data suggest that coordinated regulation of cholesterol synthesis and catabolism in the central nervous system is maintained in this model for RS. Furthermore, we speculate that the adaptive changes in these two pathways conceivably resulted from a shift in the permeability of the blood–brain barrier as implied by the significantly lower campesterol and 27‐OHC concentrations in the brains of the Mecp2^?/y mice.     

Key enzymes involved in methionine catabolism by cheese lactic acid bacteria

Cheese microbiota and their enzymatic conversion of l-methionine to volatile sulphur compounds (VSCs) play an important role in aroma formation during cheese ripening. Here, lactic acid bacteria (LAB) strains isolated from raw goats' milk cheeses were screened for the major enzymes critical to the formation of VSCs from l-methionine. A large natural biodiversity in enzyme capabilities and high inter- and intra-species variability was found among the LAB isolates investigated. From those isolates tested, lactococci displayed higher C–S lyase specificities towards the sulphur-containing compounds examined than did Lactobacillus and Leuconostoc, in some cases generating higher levels of VSCs than B. linens, known to be an efficient producer of methanethiol (MTL) and related VSCs. Moreover, these differences in C–S lyase activities (determined spectrophotometrically by measuring the formation of free thiol groups) were shown to correspond with the enzymatic potential of the isolates as determined by visualization of enzymatic activities. This technique could therefore prove valuable for the detection and preliminary characterization of C–S lyase activities among LAB isolates. Lactococci were also found to possess higher aminotransferase activities than lactobacilli and leuconostocs, while glutamate dehydrogenase activities were observed to be highest among Leuconostoc and Lactobacillus spp. Meanwhile, α-keto acid decarboxylase activities were highly variable and were measurable in only a limited number of isolates, mainly lactobacilli. From these data, combining indigenous isolates showing high VSCs-producing capabilities with those that facilitate the completion of the metabolic pathway responsible for degrading l-methionine into volatile compounds may provide an efficient approach to enhance cheese aroma development.     

蚕豆种子萌发过程中单宁代谢与钝化技术研究概述

蚕豆富含蛋白质、膳食纤维及各种维生素,是我国重要的食用豆,但含量较高的单宁限制了蚕豆的营养水平及加工品质。本文在总结蚕豆中单宁的化学结构和萌发过程中单宁的代谢途径的基础上,介绍了消除和降低蚕豆单宁含量的技术方法,以期为钝化单宁提供理论和技术支持。