Site-specific mutagenesis has been used to replace amino acid residues in the active site of human carbonic anhydrase II with residues characterizing carbonic anhydrases I. Previous studies of [Thr200----His]isoenzyme II [Behravan, G., Jonsson, B.-H. & Lindskog, S. (1990) Eur. J. Biochem. 190, 351-357] showed that His200 is important for the specific catalytic properties of isoenzymes I. In this paper some properties of two single mutants, Asn62----Val and Asn67----His, as well as a double mutant, Asn67----His/Thr200----His, are described. The results show that neither Val62 nor His67 give rise to isoenzyme-I-like properties, while the double mutant behaves like the single mutant with His200. At pH 8.9, the variant with Val62 has a higher value of kcat/Km for CO2 hydration than unmodified isoenzyme II, whereas the variant with His67 has an enhanced kcat value. The replacement of Asn62 with Val results in a 20% increase of the 4-nitrophenyl acetate hydrolase activity. For the double mutant, the esterase activity is quite close to that calculated on the assumption that the effects of the two single mutations on the free energy of activation are additive. 相似文献
The active sites of carbonic anhydrases I contain a unique histidine residue at sequence position 200. To test the hypothesis that His200 is essential for the isoenzyme-specific catalytic and inhibitor-binding properties of carbonic anhydrases I, a variant of human carbonic anhydrase II, having His200 for Thr200, was prepared by oligonucleotide-directed mutagenesis. The variant has a circular dichroic spectrum that is indistinguishable from that of the parent enzyme. The kinetics of CO2 hydration and HCO3- dehydration has been investigated. The results show that the amino acid substitution has led to changes of catalytic parameters as well as Ki values for anion inhibition in the expected directions towards the values for isoenzyme I. However, the maximal 4-nitrophenyl acetate hydrolase activity of the variant is higher than for any naturally occurring carbonic anhydrase studied so far. A detailed analysis of the kinetic observations suggests that the modification has resulted in a change of the step that limits the maximal rate of CO2 hydration at saturating buffer concentrations. This rate-limiting step is an intramolecular proton transfer in unmodified isoenzyme II and, presumably, HCO3- dissociation in the variant and in human isoenzyme I. A free-energy profile for the dominating pathway of CO2 hydration at high pH was constructed. The results suggest that the major effect of His200 is a stabilization of the enzyme-HCO3- complex by about 7.5 kJ/mol (variant) and 6.1 kJ/mol (human isoenzyme I) relative to unmodified isoenzyme II, while proton transfer between the metal site and the reaction medium is only marginally affected by the amino acid replacement. 相似文献
AbstractCo-v-culture (co-cultivations of physically separated microbes that only interact through the air) systems were designed to investigate the effects of microbial volatile organic compounds (mVOCs) from about 20 different microbes, on a medicinal fungus, Ganoderma lucidum. For more accuracy in co-cultivations, a novel synchronized cultivation approach was tested for culturing G. lucidum. The hyphal growth of G. lucidum and the content of its ganoderic acids (GAs) were measured. In almost all of the co-v-cultures, there was an inhibiting effect on hyphal growth and a promoting effect on GAs contents. In inducing GAs production, Bacillus cereus PTCC 1247 and Pseudomonas aeruginosa UTMC 1404 were the most effective ones, as, compared to control cultures, GAs content increased 2.8 fold. Comparing different co-v-cultivations demonstrated that the concentrations of mVOCs, oxygen, and carbon dioxide were the main players in co-v-cultures. No correlation was found between hyphal growth and GAs production. Strains of the same species imposed totally different effects on hyphal growth or GAs production. This study has investigated the effects of mVOCs on G. lucidum for the first time. Moreover, it suggests that co-v-cultivation may be a promising biotechnological approach to improve the production in G. lucidum. 相似文献
Molecular Biology Reports - The current study was set to assess the effect of heat stress exposure on oxidative stress, apoptosis, and endoplasmic reticulum stress markers in the cerebellum of male... 相似文献
Elevated CO2 interactions with other factors affects the plant performance. Regarding the differences between cultivars in response to CO2 concentrations, identifying the cultivars that better respond to such conditions would maximize their potential benefits. Increasing the ability of plants to benefit more from elevated CO2 levels alleviates the adverse effects of photoassimilate accumulation on photosynthesis and increases the productivity of plants. Despite its agronomic importance, there is no information about the interactive effects of elevated CO2 concentration and plant growth regulators (PGRs) on potato (Solanum tuberosum L.) plants. Hence, the physiological response and source-sink relationship of potato plants (cvs. Agria and Fontane) to combined application of CO2 levels (400 vs. 800 µmol mol−1) and plant growth regulators (PGR) [6-benzylaminopurine (BAP) + Abscisic acid (ABA)] were evaluated under a controlled environment. The results revealed a variation between the potato cultivars in response to a combination of PGRs and CO2 levels. Cultivars were different in leaf chlorophyll content; Agria had higher chlorophyll a, b, and total chlorophyll content by 23, 43, and 23%, respectively, compared with Fontane. The net photosynthetic rate was doubled at the elevated compared with the ambient CO2. In Agria, the ratio of leaf intercellular to ambient air CO2 concentrations [Ci:Ca] was declined in elevated-CO2-grown plants, which indicated the stomata would become more conservative at higher CO2 levels. On the other hand, the increased Ci:Ca in Fontane showed a stomatal acclimation to higher CO2 concentration. The higher leaf dark respiration of the elevated CO2-grown and BAP + ABA-treated plants was associated with a higher leaf soluble carbohydrates and starch content. Elevated CO2 and BAP + ABA shifted the dry matter partitioning to the belowground more than the above-media organs. The lower leaf soluble carbohydrate content and greater tuber yield in Fontane might indicate a more efficient photoassimilate translocation than Agria. The results highlighted positive synergic effects of the combined BAP + ABA and elevated CO2 on tuber yield and productivity of the potato plants. 相似文献
EcoHealth - Wild birds are important in the transmission of many zoonotic pathogens such as salmonella and avian influenza virus (AIV). The current study investigated the presence of bacterial and... 相似文献
One of the technology for increasing the safety and welfare of humans in roads is Vehicular Cloud Computing (VCC). This technology can utilize cloud computing advantages in the Vehicular Ad Hoc Network (VANET). VCC by utilizing modern equipment along with current vehicles, can play a significant role in the area of smart transportation systems. Given the potential of this technology, effective methods for managing existing resources and providing the expected service quality that is essential for such an environment are not yet available as it should. One of the most important barriers to providing such solutions seems to be resource constraints and very high dynamics in vehicles in VCC. In this article, based on virtualization and taking into account the environment with these features, we propose simple ways to manage resources better and improve the quality of service. We were able to achieve better results in simulation than previous methods by providing a flexible data structure to control the important data in the environment effectively. To illustrate the impact of the proposed methods, we compared them with some of the most important methods in this context, and we used SUMO 1.2.0 and MATLAB R2019a software to simulate them. Simulation results indicate that the proposed methods provide better results than previous methods in terms of resource efficiency, Quality of Service (QoS), and load balancing.
The genus Dorema (Apiaceae) comprises 12 accepted species, mainly growing in Asia and, particularly, in Iran, where D. ammoniacum and D. aucheri are the most used species in cuisine and folk medicine. The Dorema species are traditionally applied in the treatment of catarrh, asthma, chronic bronchitis, as carminative, mild diuretic and anthelmintic agents. In general, 42 non-volatile secondary metabolites were isolated from the 6 studied species, namely D. aitchisonii, D. ammoniacum, D. aucheri, D. glabrum, D. hyrcanum, and D. kopetdaghense. Among them, phenolic acid, flavonoid, acetophenone, coumarin, and sesquiterpene derivatives were identified as the predominant phytoconstituents. The leaves are characterized by the highest volatile content, and the sesquiterpenes in both hydrocarbon and oxygenated forms were reported as the most abundant compounds. Most of the studied pharmacological activities were assessed in vivo. Nevertheless, in vitro antiradical and antimicrobial potentials were the main investigated activities. Overall, the evaluation of bioactivities confirmed the ethnopharmacological use of the Dorema species, particularly their anti-inflammatory, antibacterial, and hypolipidemic properties. This study comprehensively overviewed, for the first time, the literature relating to the folk medicinal use and to the available phytochemical and pharmacological data. Considering the genus application and the rare clinical trials, the study of the efficacy and safety of the uninvestigated Dorema species might be an interesting and promising approach for further researches.
International Journal of Peptide Research and Therapeutics - Natural compounds extracted from marine organisms consisting of biological active materials like collagen provide a major source of... 相似文献