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11.
Thomas F. Holzman Christine C. Chung Rohinton Edalji David A. Egan Earl J. Gubbins Annemarie Rueter Gail Howard Lana K. Yang Terry M. Pederson Grant A. Krafft et al. 《Journal of Protein Chemistry》1990,9(6):663-672
The gene for human preprorenin was obtained from total RNA prepared from primary human chorion cells. An expression vector was constructed containing an SV40 early promoter, a human preprorenin cDNA, bovine growth hormone poly-A addition signal, and a dihydrofolate reductase (dhfr) expression cassette. This vector was inserted into the DXB-11 Chinese hamster ovary (CHO) cell line. The recombinant protein was exported by CHO cells into the tissue culture media. At harvest the prorenin levels ranged from 1–5 mg/L. For prorenin isolation the cell culture supernatants were processed by filtration, concentration, dialysis, and batch extraction. Preparative-scale isolation of prorenin was accomplished using blue-dye chromatography and size-exclusion chromatography. The isolated prorenin yielded a single SDS-gel band with Mr 40,000. The proprotein was characterized with respect to N-terminal sequence and N-linked sugar composition. Trypsin-activated renin prepared from the proprotein was characterized with respect to N-terminal sequence andpH-activity profile. Enzyme activity was measured with a newly developed fluorogenic peptide substrate containing the P6-P3 sequence of human angiotensinogen. 相似文献
12.
13.
Jose L. Vega Vicki L. Holmberg Edgar C. Clausen James L. Gaddy 《Archives of microbiology》1988,151(1):65-70
Intrinsic growth and substrate uptake parameters were obtained for Peptostreptococcus productus, strain U-1, using carbon monoxide as the limiting substrate. A modified Monod model with substrate inhibition was used for modeling. In addition, a product yield of 0.25 mol acetate/mol CO and a cell yield of 0.034 g cells/g CO were obtained. While CO was found to be the primary substrate, P. productus is able to produce acetate from CO2 and H2, although this substrate could not sustain growth. Yeast extract was found to also be a growth substrate. A yield of 0.017 g cell/g yeast extract and a product yield of 0.14 g acetate/g yeast extract were obtained. In the presence of acetate, the maximum specific CO uptake rate was increased by 40% compared to the maximum without acetate present. Cell replication was inhibited at acetate concentrations of 30 g/l. Methionine was found to be an essential nutrient for growth and CO uptake by P. productus. A minimum amount of a complex medium such as yeast extract (0.01%) is, however, required. 相似文献
14.
In chloroplasts and a number of prokaryotes, -aminolevulinic acid (ALA), the universal precursor of porphyrins, is synthesized by a multistep enzymatic pathway with glutamyl-tRNAGlu as an intermediate. The ALA synthesizing system from barley chloroplasts is highly specific in its tRNA requirement for chloroplast tRNAGlu; a number of other Glu-tRNAs are inactive in ALA formation although they can be glutamylated by chloroplast aminoacyl-tRNA synthetases. In order to obtain more information about the structural features defining the ability of a tRNA to be recognized by the ALA synthesizing enzymes, we purified and sequenced two cytoplasmic tRNAGlu species from barley embryos which are inactive in ALA synthesis. By using glutamylated tRNAs as a substrate for the overall reaction, we showed that Glu-tRNA reductase is the enzyme responsible for tRNA discrimination. 相似文献
15.
Ivo Šafařík 《Journal of industrial microbiology & biotechnology》1988,3(4):259-261
Summary A new insoluble chromogenic substrate for the determination of proteolytic activity was developed. This substrate was prepared by incorporating black drawing ink into casein and heating this complex at 200°C for 4 h. It is especially suitable for determining the activity of alkaline bacterial proteinases. 相似文献
16.
Synopsis Changes in the daily appetite and weekly growth rates of individual adult minnows,Phoxinus phoxinus, on ad libitum rations were recorded before and after they had experienced 4 or 16 days of food restriction. Feeding levels during the restriction periods were either starvation or a maintenance ration. The latter was estimated from a previously determined regression model. Water temperature was 15°C and the photoperiod 9L15D in all experiments. The mean weight of fish used ranged from 1.06 to 2.15 g. The 4 day restriction had no detectable effects on appetite or growth. After the 16 day restriction, the minnows showed hyperphagia and had increased specific growth rates and growth efficiencies compared with control fish. The compensatory increases in appetite and growth were not sustained and within three weeks had declined to levels not significantly different from those of the control fish. At the end of the experiments, there were no significant differences between the mean weights or cumulative food consumption of the restricted and control groups. The results suggest that adult minnows regulate their appetite and growth rate in relation to their previous nutritional history. 相似文献
17.
A biological measure of space available within substrates was used as an index to examine substrate selection by the stonefly nymph Paragnetina media (Walker). Physical measures, such as total surface area of substrate, have not worked well in the past in explaining distribution of aquatic invertebrates. Although analysis of habitable space within substrate did not explain selection completely, the technique provided a precise measure and might be a more rigorous means by which substrate selection could be examined. 相似文献
18.
Michael M. Lipsky Talia R. Sheridan Richard O. Bennett Eric B. May 《In vitro cellular & developmental biology. Plant》1986,22(6):360-362
Summary Comparisons were made of attachment and viability of rainbow trout (Salmo gairdneri) hepatocytes in short-term (2 days), primary culture on plastic, collagen-coated or extracellular matrix (ECM) coated dishes.
Hepatocyte isolation routinely yielded cells with good viability (96%). Cells plated on ECM attached with high efficiency
(93%) in contrast to cells cultured on plastic or collagen (∼20%). The cells plated on ECM flattened out and formed monolayers,
while the cells on plastic and collagen rounded up and formed multi-cell aggregates in suspension. Viability of cells in all
substrates remained high over the 2 day culture period. ECM is the first substrate to support trout-hepatocyte attachment
in primary culture. Differentiated liver function was maintained in cells cultured on ECM as evidence by the induction of
tyrosine aminotransferase by hydrocortisone (200%).
This work was supported in part by research grant R809599010 from the U. S. Environmental Protection Agency.
Editor's Statement This paper reports improved methods for culture of trout liver-derived cells that make in vitro investigations
of fish metabolism, carcinogenesis and chemical toxicity more feasible than previously applied techniques. Recent interest
in fish as models for study and indicators of effects of envionmental and food-related toxins make this work timely, poarticularly
since many of the compounds of interest are primarily metabolized by hepatocytes or act on liver as a major target. David
W. Barnes 相似文献
19.
Göran Wingstrand 《Physiologia plantarum》1985,64(2):223-229
Membrane-bound MgATPase activity from roots of young sugar beet ( Beta vulgaris L. cv. Monohill) was investigated in a membrane fraction purified by partition in an aqueous polymer two-phase system. After two steps of "washing" with fresh bottom phase (rich in dextran), the polyethylene glycol rich top phase (U3 ) was practically free of mitochondrial membranes (cytochrome oxidase), and the remaining MgATPase activity showed high substrate specificity for ATP. An optimum for the MgATPase activity was found at pH 7. The activation by Na+ or K+ was strongest on the acid side without any observable shift in pH optimum. Oligomycin had no effect, but vanadate strongly inhibited the U3 MgATPase and the K+ activation was lost. The complex activation pattern achieved by varying the Na+ /K+ ratio at constant total concentration was interpreted as a synergistic (Na+ + K+ )-activation. The U3 fraction MgATP-ase activity showed a 4-fold increase in the presence of 0.01% Triton X-100 implying that the MgATPase activity is located in vesicles of which 75% or more are sealed with the ATP binding site on the inside. Comparison with the properties of plasma membrane. ATPases from other plants indicated that the U3 fraction MgATPase was mainly of plasma membrane origin. 相似文献
20.
Summary Fully filled spikelets were determined by specific gravity method in some rice varieties. As specific gravity increased, the filled spikelets decreased while the test weight (1000-grain weight) increased. The potential test weight was found to be more than the weight known for the variety. Different grades of grain were characterised as (i) average (ii) good and (iii) Very good based on the degree of spikelet filling. The fully fitted spikelets were found to be lower in all the varieties tested and the partially filled but useful for yield calculations were higher. The grain grade index denotes the proportion of fully filled spikelets recovered at 1.18 specific gravity to the total number of spikelets formed. It was suggested that this inded is useful as a screening tool in varietal improvement programme for identifying high yield potential plants. 相似文献