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81.
Three cases of abnormal expression of the equine protease inhibitory alleles, Pi F, L, and S1, were observed following the examination of 30,000 plasma samples by one-dimensional acid (pH 4.6) polyacrylamide gel electrophoresis. Characterization of the abnormal proteins in terms of isoelectric point, molecular mass, inhibitory spectra, and sialic acid content was performed using one- and two-dimensional electrophoretic techniques. The Pi F and S1 abnormalities were postulated to be the result of amino acid substitutions causing alterations in the processing of the carbohydrate side chains. No explanation could be offered for the Pi L abnormality other than a charge shift mutation. Abnormal types, F*, L*, and S*1 behaved as alleles but the distribution of L* in offspring from one stallion (present in only 6 of 83 offspring) differed significantly from expectation.This work was supported by a grant from the Australian Stud Book, Alison Road, Randwick, N.S.W. 2031. 相似文献
82.
Summary Conditions were used where the action of porcine pancreatic phospholipase A2 on phospholipids can be followed in the absence of added calcium and the catalytic activity is supported by the calcium brought with the nanomolar enzyme. Therefore, alterations in the enzyme velocity resulting from the presence of spermine or spermidine could be specifically studied using 1-palmitoyl-2-(pyren-1-yl)hexanoyl-sn-glycero-3-phosphocholine (PPHPC) and 1-palmitoyl-2-(pyren-1-yl)hexanoyl-sn-glycero-3-phosphoglycerol (PPHPG) as substrates. Both spermine and spermidine activated the hydrolysis of PPHPG fourfold at polyamine/phospholipid molar ratios of approximately 11 and 121, respectively. Double-reciprocal plots of enzyme activityvs. PPHPG concentration revealed the enhancement to be due to increased apparentV
max while the apparentK
m
was slightly increased. In the presence of 4mm CaCl2 inhibition by polyamines of PPHPG hydrolysis by phospholipase A2 was observed. Using synthetic diamines we could further demonstrate that two primary amino groups are required for the activation. In the absence of exogenous CaCl2 polyamines inhibited the hydrolysis of PPHPC by phospholipase A2. The presence of 4mm CaCl2 reversed this inhibition and a twofold activation was observed at 10 m spermine. The results obtained indicate that the activation of PLA2 by spermine and spermidine is produced at the level of the substrate, PPHPG. This implies the formation of complexes of phosphatidylglycerol and polyamines with defined stoichiometries. 相似文献
83.
Summary A pot experiment with lettuce involving three N forms each at six application levels, showed that lettuce can be grown satisfactorily
with a very low nitrate content when supplied with ammonium sulphate and a nitrification inhibitor. For plants growing on
nitrate N, the optimum midrib sap nitrate concentration as maturity approached was about 1400 mg/1 NO3-N. Large losses of mineral N were observed from the peat medium, even in the absence of plants.
A relationship is presented which would enable a lettuce grower to estimate whole-shoot nitrate concentration from a quick
test of midrib sapi.e. NO3-N (mg/kg in fresh shoot) =0.14×NO3-N (mg/l in sap).
Tipburn was worst at intermediate levels of applied N, and was less serious with pure ammonium nutrition than with nitrate. 相似文献
84.
Summary In order to improve nitrogen recovery by rice, the effect of a urease inhibitor phenylphosphorodiamidate (PPD) on the efficiency
of fertilizer urea was studied in laboratory and greenhouse. Addition of PPD to urea (5% w/w) delayed urea hydrolysis by 3
to 4 days and reduced ammonia volatilization from 45% (without PPD) to 8.5% (with PPD). Ammonia volatilization obeyed first
order kinetics. Urea hydrolysis was sufficiently strongly inhibited to match the nitrification potential of the soil. N application
to rice by three different modes showed that a delayed mode (4 splits) was superior to two conventional modes (3 splits) in
nitrogen recovery and fertilizer efficiency since it met nitrogen requirement of plants at reproductive stage. In 2 out of
3 modes of application, there was a 14% increase (relative) in grain yields and dry matter, and 6.8% increase in N uptake
efficiency on application of PPD along with urea. The results indicate that urease inhibitors like PPD can be effectively
used to block urea hydrolysis, reduce ammonia volatilization losses and improve N use efficiency by rice. 相似文献
85.
Extracellular Fluid Proteins of Goldfish Brain: Evidence for the Presence of Proteases and Esterases 总被引:1,自引:1,他引:0
Preparations of enriched fractions of extracellular fluid (ECF) proteins from goldfish brain were found to contain protease(s) and esterase(s). The N-substituted furanacryloyl (FA) peptides FA-Phe-Gly-Gly and FA-Phe-OMe were used as model substrates for determining protease and esterase activity, respectively, in a spectrophotometric assay. Studies of the profile of substrate specificity and identification of the types of compounds that were effective as inhibitors showed that these ECF enzymes have some distinctive properties. GSH, but not GSSG, and EDTA inhibited the protease(s) without influencing the esterase(s), whereas L-1-tosylamide-2-phenylethylchloromethyl ketone blocked both protease and esterase activities of ECF. Most of the protease and esterase properties of ECF could be bound to concanavalin A-Sepharose affinity chromatographic columns in association with ependymin--a brain extracellular protein. These observations indicate that ECF may contain a metalloprotease(s) and raise the possibility that the ependymins might be a substrate for these ECF enzymes. 相似文献
86.
Cells subjected to the events occurring before, during, and after freezing and thawing are exposed to major changes in the
osmotic pressure of the surrounding medium; i.e., the osmolalities can exceed 30. An important question in understanding the
mechanisms of injury is whether cells respond as ideal osmometers to these strongly anisotonic solutions. Mouse and bovine
embryos from eight-cell to blastocyst stage were used to investigate the question. They were found to behave as ideal osmometers
at room temperature over a wide range of tonicities; i.e., from four times isotonic to almost 1/3 times isotonic, ideality
being defined by a Boyle-van't Hoff equation. Embryo volumes increased from 40 to 200% of isotonic over this range and survivals
of mouse embryos were unaffected. However, outside this range the membrane apparently becomes leaky and the survival of mouse
embryos drops sharply. Osmolalities rise to high values during freezing and the paper develops the thermodynamic equations
to show how computed cell volumes as a function of subzero temperature can be translated into the Boyle-van't Hoff format
of cell volume as a function of the reciprocal of osmolality. 相似文献
87.
烟草愈伤组织器官发生过程中外源激素的作用 总被引:6,自引:0,他引:6
近年来,利用愈伤组织系统在与器官发生有关的形态学、生理学和生物化学研究方面已经取得了一些进展(Thorpe 1980,刘涤 1983)。对烟草愈伤组织系统的研究明确了外源激素对器官发生类型的调节作用(Skoog 1971,Engelke等1973,刘涤等1980)。但是,这些研究仅考虑到外源激素的作用,而对器官发生过程中的其它变化并不了解。最近,Kamada和Harada(1981)比较了胡萝卜体细胞胚发育过程中内源IAA和ABA含量的变化,Noma等(1982)证实形成胚的和不形成胚的细胞间GA_3含 相似文献
88.
Summary The presence of a coupled Na+/Ca2+ exchange system has been demonstrated in plasma membrane vesicles from rat pancreatic acinar cells. Na+/Ca2+ exchange was investigated by measuring45Ca2+ uptake and45Ca2+ efflux in the presence of sodium gradients and at different electrical potential differences across the membrane (=) in the presence of sodium. Plasma membranes were prepared by a MgCl2 precipitation method and characterized by marker enzyme distribution. When compared to the total homogenate, the typical marker for the plasma membrane, (Na++K+)-ATPase was enriched by 23-fold. Markers for the endoplasmic reticulum, such as RNA and NADPH cytochromec reductase, as well as for mitochondria, the cytochromec oxidase, were reduced by twofold, threefold and 10-fold, respectively. For the Na+/Ca2+ countertransport system, the Ca2+ uptake after 1 min of incubation was half-maximal at 0.62 mol/liter Ca2+ and at 20 mmol/liter Na+ concentration and maximal at 10 mol/liter Ca2+ and 150 mmol/liter Na+ concentration, respecitively. When Na+ was replaced by Li+, maximal Ca2+ uptake was 75% as compared to that in the presence of Na+. Amiloride (10–3 mol/liter) at 200 mmol/liter Na+ did not inhibit Na+/Ca2+ countertransport, whereas at low Na+ concentration (25 mmol/liter) amiloride exhibited dose-dependent inhibition to be 62% at 10–2 mol/liter. CFCCP (10–5 mol/liter) did not influence Na+/Ca2+ countertransport. Monensin inhibited dose dependently; at a concentration of 5×10–6 mol/liter inhibition was 80%. A SCN– or K+ diffusion potential (=), being positive at the vesicle inside, stimulated calcium uptake in the presence of sodium suggesting that Na+/Ca2+ countertransport operates electrogenically, i.e. with a stoichiometry higher than 2 Na+ for 1 Ca2+. In the absence of Na+, did not promote Ca2+ uptake. We conclude that in addition to ATP-dependent Ca2+ outward transport as characterized previously (E. Bayerdörffer, L. Eckhardt, W. Haase & 1. Schulz, 1985,J. Membrane Biol.
84:45–60) the Na+/Ca2+ countertransport system, as characterized in this study, represents a second transport system for the extrusion of calcium from the cell. Furthermore, the high affinity for calcium suggests that this system might participate in the regulation of the cytosolic free Ca2+ level. 相似文献
89.
The changes of H-D exchange rates upon protein-protein interactions are generally interpreted as a result of the changes of the dynamic properties of the proteins. The effect of trypsin binding on the H-D exchange kinetics of some trypsin inhibitor amide H's was reported (Simon et al., 1984). In this paper the electrostatic potential originating from the trypsin molecule is calculated at the positions of the studied amide H's in the trypsin-trypsin inhibitor complex. We conclude that the observed decrease of the exchange rates is mainly due to the electrostatic field of the trypsin molecule. 相似文献
90.
Pancreatic hypertrophy and hyperplasia following chronic joint (CA + SE), or separate, caerulein (CA: 1 microgram . kg-1) and secretin (SE: 75 micrograms . kg-1) administration were studied in parallel with pancreatic somatostatin (SRIF) contents following 2, 4, 7 and 10 days of treatment. Parameters indicative of pancreatic growth (tissue weight, DNA and protein contents, cellular protein concentrations) increased significantly after 2 days of CA or CA + SE and reached a plateau between days 4 and 10. SE merely induced a mild hypertrophy after 4 days. Endogenous pancreatic SRIF contents varied upon treatment, differently so with each peptide regimen. Indeed, CA and CA + SE treatments decreased total SRIF contents after 2 days with no effect thereafter. SE also decreased the latter after 2 days while significant increases were observed after 7 and 10 days. The inverse relationship seemingly existing between SRIF contents and the amplitude of hormonally-induced pancreatic growth supports the hypothesis that endogenous pancreatic SRIF, operating as an 'antigrowth' factor, may participate in the exogenous CA, SE and CA + SE stimulated pancreatic growth phenomena. 相似文献