Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.4 (trypsin)
 42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Binding of tRNA(Met/f) to the monomeric trypsin-modified methionyl-tRNA synthetase turns off the methionine-dependent isotopic ATP--PPi exchange. In the case of the dimeric native methionyltRNA synthetase, one anticooperatively bound tRNA(Met/f) inhibits the exchange by only 50%. These behaviours of tRNA do not require the integrity of the 3'-terminal adenosine. Esterification by methionine of the 3' end of tRNA reinforces the affinity of tRNA(Met/f)for the enzymes. In the case of the native enzyme, due to this effect, a second binding mode for methionyl-tRNA may be demonstrated through the isotopic exchange. This additional binding of tRNA corresponds to the expression of the anticooperatively blocked tRNA binding site. Methionine reverses competitively the reinforcing effect of the esterified methionyl moiety on tRNA binding. It is concluded that after esterification of tRNA, the aminoacyl residue still binds the enzyme, probably within the methionine activating site. The latter behaviour may account for the observation that excess methionine accelerates the aminoacylation turnover rate of tRNA(Met/f).
 ...
PMID:Interrelation between transfer RNA and amino-acid-activating sites of methionyl transfer RNA synthetase from Escherichia coli. 33 59

A latent ATP-dependent Ca storage system is enriched in preparations of pinched-off presynaptic nerve terminals (synaptosomes), and is exposed when the terminals are disrupted by osmotic shock or saponin treatment. The data indicate that a fraction of the Ca uptake (measured with 45Ca) is associated with the intraterminal mitochondria; it is blocked by ruthenium red, by FCCP, and by azide + dinitrophenol + oligomycin. There is, however, a residual ATP-dependent Ca uptake that is insensitive to the aforementioned poisons; this (nonmitochondrial) Ca uptake is blocked by tetracaine, mersalyl and A-23187. Moreover, A-23187 rapidly releases previously accumulated Ca from these (nonmitochondrial) storage sites, whereas the Ca chelator, EGTA, does not. The proteolytic enzyme, trypsin, spares the mitochondria but inactivates the nonmitochondrial Ca uptake mechanism. Chemical measurements of total Ca indicate that the ATP-dependent Ca uptake at the nonmitochondrial sites involves the net transfer of Ca from medium to tissue fragments. This system can sequester Ca when the ambient-ionized Ca2+ concentration (buffered with EGTA) is less than 0.3 micrometer; brain mitochondria take up little Ca when the ionized Ca2+ level is this low. Preliminary subfractionation studies indicate that the nonmitochondrial Ca storage system does not sediment with synaptic vesicles. We propose that this Ca storage system, which has many properties comparable to those of skeletal muscle sarcoplasmic reticulum, may be associated with intraterminal smooth endoplasmic reticulum. This Ca-sequestering organelle may help to buffer intracellular Ca.
 ...
PMID:Calcium buffering in presynaptic nerve terminals. I. Evidence for involvement of a nonmitochondrial ATP-dependent sequestration mechanism. 35 58

E. coli K10 was found to grow anaerobically on molecular hydrogen by reducing nitrate, fumarate, and trimethylamine N-oxide when peptone was added to the culture medium. Molar growth yields based on consumed hydrogen estimated from the amounts of reduction products were all 7.8 g cells/mol, suggesting that 1 mol of ATP was produced in the oxidation of 1 mol of hydrogen. Hydrogenase activity measured in terms of hydrogen evolution was several times higher in cells grown on glucose than in cells grown on hydrogen in the presence of fumarate and trimethylamine N-oxide, while hydrogenase activity measured in terms of hydrogen uptake was unchanged in both cases. The ratio of hydrogenase activities measured in terms of hydrogen uptake and evolution was also high in the extract and centrifugal fractions from cells grown in hydrogen. The soluble fraction and trypsin digest of the precipitate at 100,000 X g were subjected to polyacrylamide disc gel electrophoresis and hydrogenase bands were stained by reduction of benzyl viologen with hydrogen and by oxidation of reduced methyl viologen. The resulting patterns suggest that multiple forms of hydrogenase are present and that the amounts of forms functioning in hydrogen evolution were greatly decresed in cells grown on hydrogen in the presence of acceptors.
 ...
PMID:Hydrogen-dependent growth of Escherichia coli in anaerobic respiration and the presence of hydrogenases with different functions. 36 3

Native and trypsin-modified methionyl-tRNA synthetases from Escherichia coli were found to be inactivated by incubation in the presence of Co(III) complexes of ATP, stabilized either by imidazole or phenanthroline, or by oxidation in situ to Co(III) of the substrate ATP-Co(II). It has been shown that the inactivation proceeds by specific labeling of the catalytic ATP-Mg(II) site of the synthetases. The enzymes are completely inactivated by the incorporation of one cobalt atom and one ATP molecule per active site. The inactivated enzymes may be stored for a long period without significant reactivation or removal of the cobalt label. In the presence of dithiothreitol or 2-mercaptoethanol, the labeled enzymes recover full activity with concomittant release of the bound label molecules.
 ...
PMID:Cobalt(III) labeling of methionyl-tRNA synthetase from Escherichia coli. 37 61

Acetylene reduction catalyzed by nitrogenase from Rhodospirillum rubrum has low activity and exhibits a lag phase. The activity can be increased by the addition of a chromatophore membrane component and the lag eliminated by preincubation with this component, which can be solubilized from chromatophores by treatment with NaCl. It is both trypsin- and oxygen-sensitive. Titration of the membrane component with nitrogenase and vice versa shows a saturation point. The membrane component interacts specifically with the Fe protein of nitrogenase, the interaction being ATP- and Mg2+-dependent.
 ...
PMID:Necessity of a membrane component for nitrogenase activity in Rhodospirillum rubrum. 41 Apr 46

Previous studies have shown that platelet membranes bind radiolabeled ADP and have nucleoside diphosphokinase activity which transforms added ADP to ATP. In order to further characterize these reactions, the ADP-binding and nucleoside diphosphokinase activity of purified platelet membranes were solubilized by freeze-thaw injury followed by extraction with isotonic buffered saline. Up to 80% of membrane ADP-binding activity was solubilized along with 20% of the total membrane protein, a 4-fold purification. A Millipore filter binding assay was developed to detect the soluble binding protein using [3H]ADP as radioligand. Binding of [3H]ADP was rapid, reversible, saturable, and was destroyed by heat, trypsin digestion, and 1 mM N-ethylmaleimide. By Scatchard analysis, there was a single class of binding sites with a Kd of 3.8 x 10(-7) M. Unlabeled nucleotides competed with [3H]ADP with the following potency series: ATP = ADP greater than AMP greater than adenosine. The solubilized nucleoside diphosphokinase activity could be separated from ADP-binding activity by ultracentrifugation on 5 to 20% sucrose density gradients containing 0.6 M KCl suggesting that the activities reside on separate molecules. Hydrodynamic parameters were calculated for the binding protein by gel filtration and ultracentrifugation. The s20,w was 4.1, Stoke's radius 35 x 10(-8)cm, axial ratio (f/fo) 1.09, and the Mr = 61,000. The studies suggest that this platelet ADP-binding protein may act as the receptor for initiating ADP-induced aggregation and release.
 ...
PMID:Solubilization and characterization of a platelet membrane ADP-binding protein. 43 64

We observed that hamster caudal epididymal (HCE) plasma could inhibit dilution damage in HCE sperm. Here it is shown that in the absence of HCE plasma survival factors (SF), dilution of HCE sperm led to apparently simultaneous lysis and loss of motility. However, in the presence of HCE plasma, lysis did not occur when HCE sperm motility was blocked by palytoxin. Using a newly developed microassay for SF, significant amounts of SF activity were detected in dog and bovine caudal epididymal plasma, hamster testes exudate, HCE sperm cytosol, human seminal plasma, hamster and bovine adrenal extracts, hen's egg, and human serum. The SF activity of HCE plasma could tolerate restricted periods of boiling or pH extremes but was destroyed by trypsin and protease. Unlike human serum, HCE plasma did not significantly alter HCE sperm respiration or ATP content.
 ...
PMID:Studies on factors in hamster caudal epididymal plasma and other sources which inhibit sperm dilution damage. 45 36

Study of endocytosis in human erythrocytes and their ghosts provides an opportunity for the elucidation of the steps involved in membrane invagination and fusion. The specific preparation being studied should be described with great care since circumstances that produce endocytosis may differ among the several available preparations. For example, in resealed red ghosts the addition of 0.5 to 1 mM Ca stimulates Mg-ATP-induced endocytosis, whereas in intact erythrocytes Ca addition stimulates primaquine-induced endocytosis and inhibits vinblastine-induced endocytosis. Furthermore, Ca inhibits endocytosis in white ghosts. EDTA can produce endocytosis in white ghosts but not in resealed red ghosts. In studies with white ghosts, incubation with EDTA, trypsin, or Mg-ATP produced endocytosis, whereas the prior addition of an antispectrin antibody prevented endocytosis. When the white ghost vacuoles were harvested they were found to be depleted of spectrin. These observations lead to the hypothesis that endocytic vacuoles are formed in areas of the membrane that have been substantially freed of spectrin.
 ...
PMID:Endocytosis in erythrocytes and their ghosts. 53 Oct 34

Some of the effects of native bovine parathyroid hormone and of the synthetic aminoterminal 1-34 fragment on the adenylate cyclase activity of human fat cell ghosts were studied. Saturating concentrations of both hormone preparations caused a significant increase of enzyme activity by about 200-300%. Guanosine 5'-triphosphate (0.1 mM) inhibited basal enzyme activity but had no substantial effect on parathyroid hormone-stimulated enzyme activity. The guanosine 5'-triphosphate analogue, 5'-guanylyl-imidodiphosphate, produced about a threefold enhancement of basal and parathyroid hormone-stimulated enzyme activities under standard conditions (5 mM Mg+2, 1mM ATP, pH 8.0, 30 degrees C). Activation by parathyroid hormone was not influenced by beta-adrenergic blockade in contrast to stimulation by epinephrine. The sensitivity of the enzyme system to the native and the synthetic parathyroid hormone was, however, abolished after pretreatment of the fat cells with trypsin (1 mg/ml). The stimulatory effects of epinephrine and NaF were not affected by pretreatment with trypsin. The results suggest that human fat cells, like rat adipocytes, contain a multireceptor-coupled adenylate cyclase.
 ...
PMID:Adenylate cyclase of human fat cell ghosts. Stimulation of enzyme activity by parathyroid hormone. 55 1

Partially purified flounder muscle (Pseudopleuronectus americanus) glyceraldehyde 3-phosphate dehydrogenase was immobilized on cyanogen bromide-activated Sepharose. The catalytic properties of the immobilized preparation were studied to determine if immobilization alters the kinetic properties of the native holoenzyme. The results indicate that the pH activity profile of immobilized glyceraldehyde 3-phosphate dehydrogenase did not differ from that of the native enzyme. The Michaelis constants (Km) for NAD and glyceraldehyde 3-phosphate were somewhat altered. The enzyme stability toward various inactivation treatments in the presence and absence of NAD was characterized and compared to that of he native enzyme. When either form of the enzyme was incubated with urea at concentrations greater than 2M, inactivation occurred very rapidly. Incubation in 0.1% trypsin for 60 minutes decreased the activity of immobilized glyceraldehyde 3-phosphate dehydrogenase by 45% and of the native soluble enzyme by 70%. The immobilized enzyme also exhibited considerably more stability than the native soluble enzyme when exposed to a temperature of 50 degrees or to 20 mM ATP. In all cases NAD either greatly reduced the rate of inactivation or completely protected the enzyme from inactivation.
 ...
PMID:Immobilized flounder muscle glyceraldehyde 3-phosphate dehydrogenase. 56 63


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>