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81.
Abstract. Woody biomass production in natural forests of arid and semi-arid regions is low. The fuelwood demand of settlements often exceeds the sustained yield and regeneration capacity of natural forests, which results in deforestation. Regeneration and woody biomass development was studied in cleared Acacia zanzibarica bushland in Bura, eastern Kenya. The area was cleared in 1982 and studied in 1988. The site had been colonized primarily by Acacia zanzibarica and A. reficiens. Mean density was 1333 trees/ha, mean total woody biomass (dry weight) 1954 kg/ha, equal to 2.53 m3/ha. Mean annual increment was 293 kg/ha, or 0.3 8m3/ha. Expressed as rain use efficiency, the natural dry matter productivity of the woody component equals 0.83 kg ha-1 yr-1 mm-1. The regeneration potential and some management implications are discussed. 相似文献
82.
R Wibom E Hultman M Johansson K Matherei D Constantin-Teodosiu P G Schantz 《Journal of applied physiology》1992,73(5):2004-2010
The adaptation of mitochondrial ATP production rate (MAPR) to training and detraining was evaluated in nine healthy men. Muscle samples (approximately 60 mg) were obtained before and after 6 wk of endurance training and after 3 wk of detraining. MAPR was measured in isolated mitochondria by a bioluminometric method. In addition, the activities of mitochondrial and glycolytic enzymes were determined in skeletal muscle. In response to training, MAPR increased by 70%, with a substrate combination of pyruvate + palmitoyl-L-carnitine + alpha-ketoglutarate + malate, by 50% with only pyruvate + malate, and by 92% with palmitoyl-L-carnitine + malate. With detraining MAPR decreased by 12-28% from the posttraining rate (although not significantly for all substrates). No differences were found when MAPR was related to the protein content in the mitochondrial fraction. The largest increase in mitochondrial enzyme activities induced by training was observed for cytochrome-c oxidase (78%), whereas succinate cytochrome c reductase showed only an 18% increase. The activity of citrate synthase increased by 40% and of glutamate dehydrogenase by 45%. Corresponding changes in maximal O2 uptake were a 9.6% increase by training and a 6.0% reversion after detraining. In conclusion, both MAPR and mitochondrial enzyme activities are shown to increase with endurance training and to decrease with detraining. 相似文献
83.
Biophysical studies of engineered mutant proteins based on calbindin D9k modified in the pseudo EF-hand 总被引:3,自引:0,他引:3
C Johansson P Brodin T Grundstr?m E Thulin S Forsén T Drakenberg 《European journal of biochemistry》1990,187(2):455-460
The genes for four mutant proteins from calbindin D9k, all with mutations in the N-terminal Ca2+-binding domain (pseudo EF-hand) have been synthesized and expressed in Escherichia coli. The purification scheme has been modified to minimize the formation of deamidated proteins. The set of modifications in the pseudo EF-hand is an attempt to turn this site into a structure resembling an archetypal EF-hand, with its characteristic 113Cd-NMR shift (-80 to -110 ppm) and high calcium-binding constants, whereas the C-terminal Ca2(+)-binding site (EF-hand) is kept intact in all mutant proteins. The mutant proteins studied here all have pseudo EF-hands with a lower calcium-binding constant and a higher calcium off-rate to the pseudo EF-hand than the wild-type protein. From the results obtained it is obvious that proline 20 in the pseudo EF-hand, which has been deleted or replaced by glycine in three of the mutants, has a stabilizing effect on calcium binding to that site. Furthermore, the modifications in the pseudo EF-hand seem to have only a local effect, leaving the tertiary structure of the protein and the calcium-binding properties of the unmodified site virtually unchanged. 相似文献
84.
A 2-fold increase in the level of epidermal growth factor (EGF) receptor mRNA accompanied by a similar increase in newly synthesized ligand-binding EGF-receptors was observed 2-4 h after intraportal EGF-injections and 2-4 h after partial hepatectomy. After this initial increase, the EGF-receptor levels decreased back to control levels 6-8 h after EGF-injections and below control levels 6-8 h after partial hepatectomy. EGF was also found to influence the degradation of endocytosed [125I]-EGF 3 h after injection to a similar extent as partial hepatectomy. The similar effects of EGF and partial hepatectomy suggests that EGF or EGF-like factors may be mechanistically involved in the early "promotion" stage during the pre-replicative phase of liver regeneration. The EGF-induced effects are, however, at least not alone responsible for the replicative process. 相似文献
85.
Protein surface charges and Ca2+ binding to individual sites in calbindin D9k: stopped-flow studies 总被引:3,自引:0,他引:3
The kinetics of calcium dissociation from two groups of site-specific mutants of calbindin D9k--a protein in the calmodulin superfamily with two Ca2+ sites and a tertiary structure closely similar to that of the globular domains of troponin C and calmodulin--have been studied by stopped-flow kinetic methods, using the fluorescent calcium chelator Quin 2, and by 43Ca NMR methods. The first group of mutants comprises all possible single, double, and triple neutralizations of three particular carboxylate groups (Glu-17, Asp-19, and Glu-26) that are located on the surface of the protein. These carboxylates are close to the two EF-hand calcium binding sites, but are not directly liganded to the Ca2+ ions. Conservative modification of these negative carboxylate side chains by conversion to the corresponding amides results in a marked reduction in the Ca2+ binding constants for both sites, as recently reported [Linse et al. (1988) Nature 335, 651-652]. The stopped-flow kinetic results show that this reduction in Ca2+ affinity derives primarily from a reduction in the Ca2+ association rate constant, kon. The estimated maximum value of the association rate constant (kon(max) for Ca2+ binding to the wild-type protein is ca. 10(9) M-1 s-1. In contrast, for the mutant protein with three charges neutralized the maximum association rate constant is estimated to be only 2 X 10(7) M-1 s-1.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
86.
The freezing point of aqueous two-phase (liquid-liquid) systems containing water, dextran and poly(ethylene glycol) has been lowered by including glycerol. Biological membranes, obtained by fragmentation of a crude synaptosomal preparation from calf brain cortex, have been included in the two-phase systems. The effects of temperature and the concentration of glycerol on the partition of the membranes within the systems have been investigated. Considerable stabilisation of the membranes was noticed when they were partitioned at -10 degrees C compared with 0 degrees C. The influences of glycerol, ethylene glycol, N,N-dimethylformamide and tetrahydrofuran on the phase-forming properties of the systems and on enzyme activities are also presented. Possible use of the above systems for studies and separation of biological membranes are discussed. 相似文献
87.
In order to study the impact of high-density lipoproteins (HDL) subclasses on the ability of HDL to act as substrate for lecithin: cholesterol acyltransferase (LCAT), we isolated HDL from nine normolipidemic male subjects. The HDL particle size distribution was analysed by gradient gel electrophoresis and the esterification rate of the isolated homologous HDL was compared with a pool of HDL where all the nine subjects took part. It was found that the strongest determinant for HDL cholesterol esterification rate was the inhibitory action of HDL subclass 2B. 相似文献
88.
P Brodin C Johansson S Forsén T Drakenberg T Grundstr?m 《The Journal of biological chemistry》1990,265(19):11125-11130
We have constructed three different engineered proteins based on calbindin D9K by either exchanging the two calcium binding sites within the protein or making the amino acid sequence of the two calcium binding sites identical. The individual calcium binding sites of the engineered proteins retain most of their ion binding characteristics as well as the basal structure of their Ca2+ ligand sphere in the new environment. Even the protein with its sites interchanged, a mutation involving 30 amino acids out of a total of 75, still binds calcium with an affinity as high as that of many natural EF-hand proteins. 相似文献
89.
John A. Buswell Karl-Erik Eriksson Jugal K. Gupta Sven G. Hamp Inger Nordh 《Archives of microbiology》1982,131(4):366-374
Metabolism of vanillic acid, a product of lignin degradation, has been studied in selected representatives of soft-rot, brown-rot and white-rot fungi. All of the brown-and white-rot species examined decarboxylated vanillate to methoxyhydroquinone oxidatively. Mycelium extracts of all these fungi, except Pleurotus ostreatus contained high levels of an NAD(P)H-dependent vanillate hydroxylase. P. ostreatus also released 14CO2 from 14COOH-vanillate but by a different mechanism possibly involving phenoloxidases. Most of these fungi also contained a dioxygenase which catalysed the intra-diol cleavage of hydroxyquinol (1,2,4-trihydroxybenzene) to form maleylacetate. No 3-O-demethylase activity was detected, and data indicate that in some of the fungi examined cleavage of the aromatic ring occurs without prior removal of the methoxyl group. None of the soft-rot fungi tested contained vanillate hydroxylase or hydroxyquinol 1,2-dioxygenase, but very low levels of protocatechuate 3,4-dioxygenase were detected in mycelium extracts. Vanillate catabolism among members of this group occurs via a different route which may involve ring demethylation although no 3-O-demethylase activity was detected in this study. The enzyme NAD(P)H-quinone oxidoreductase was demonstrated to exist in all the studied groups of fungi. 相似文献
90.
We have studied the changes in the activities of both nitrogenase (switch off) and glutamine synthetase in Rhodospirillum rubrum upon addition of ammonium ions or glutamine to nitrogen fixing cultures. Both activities decrease drastically and return in a parallel manner when added ammonia is metabolized. The decrease in glutamine synthetase activity does not seem to be primarily due to adenylylation of the enzyme. Addition of glutamine to cells starved for nitrogen results in inactivation of glutamine synthetase but nitrogenase is only partially switched off.Abbreviations CeMe3NBr
Cetyltrimethylammonium bromide
- Hepes
N-2-hydroxyethyl-piperazine-N-2 sulfonic acid
- MSO
methionine-D,L-sulfoximine
- Tea-Dmg
triethanol amine-3,3-dimethylglutaric acid 相似文献