PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Enzyme Activation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1998

A less acidic human follicle-stimulating hormone preparation induces tissue-type plasminogen activator enzyme activity earlier than a predominantly acidic analogue in phenobarbital-blocked pro-oestrous rats.

Follicle-stimulating hormone (FSH) exists in multiple molecular forms. In both experimental animals and in humans the production and secretion of less acidic, short-lived FSH glycoforms significantly increase during the peri-ovulatory period. To gain further insights on the physiological role of these FSH variants, we analysed the ability of two FSH compounds, recombinant FSH (rFSH) and purified FSH from urinary origin (uFSH), (less acidic and acidic pattern of FSH charge isoform distributors respectively) to induce ovarian tissue-type plasminogen activator (tPA) enzyme activity in vivo. FSH produced by Chinese hamster ovary cells and highly purified uFSH were injected at 15:00 h on the pro-oestrous day into phenobarbital-blocked rats and the ovaries were analysed for tPA enzyme activity and tPA mRNA concentrations at different times after FSH injection. Induction of tPA enzyme activity by uFSH and rFSH showed distinct dynamics depending on the particular preparation administered. In animals treated with uFSH, maximum tPA enzyme activity was detected at 20:00 h, and maximum tPA mRNA concentrations were detected at 17:00 h. tPA enzyme activity induction by rFSH was at the maximum at 17:00 h, and maximum tPA mRNA concentration was at 16:00 h (P< 0.05 for uFSH versus rFSH). All animals in the uFSH- and rFSH-treated groups and none in phenobarbital-blocked, saline-treated controls ovulated. No significant differences were present in the number of ova shed by rats treated with uFSH or rFSH and spontaneously ovulating rats (10.7+/-1.7, 10.0+/-2.6 and 11.3+/-1.6 respectively). These data indicate that the increased biological activity exhibited by less acidic FSH glycovariants at the target cell level may compensate for the drawback imposed by their relatively short plasma half-life.

Animals↗
PubMed1982

The mitochondrial adenosine triphosphatase of Acanthamoeba castellanii. Oscillatory accumulation of enzyme activity, enzyme protein and F1-inhibitor during the cell cycle.

1. The mitochondrial ATPase of Acanthamoeba castellanii accumulated discontinuously in synchronous cultures prepared by a minimally perturbing size-selection technique. 2. Enzyme activity per ml of culture doubled overall during one cell cycle time of 8 h, but oscillated to give seven maxima during this period. Similar oscillations were observed in the specific activities of ATPase and of the naturally occurring inhibitor protein. 3. These variations in enzyme activity reflected changes in amount of enzyme protein as assayed by an immunological technique. 4. Large variations in I50 values (micrograms of inhibitor/mg of protein necessary for 50% inhibition of inhibitor-sensitive activity) for inhibition of ATPase activity by seven different inhibitors of energy conservation were observed. Activity was more sensitive to inhibition by oligomycin, efrapeptin, citreoviridin and quercetin when values were highest. 5. The results are discussed in relation to the phased organization of biosynthesis and degradation of cellular components known to occur during the cell cycle of this organization.

Adenosine Triphosphatases↗
PubMed1998

A naturally occurring basically charged human follicle-stimulating hormone (FSH) variant inhibits FSH-induced androgen aromatization and tissue-type plasminogen activator enzyme activity in vitro.

It is well known that deglycosylation of gonadotropins by enzymatic or chemical procedures or by deletion of sites for N-linked glycosylation produces antagonistic analogs which are able to interact strongly with the receptor and to inhibit binding of the wild-type hormone. In the present study, we analyzed the antagonistic properties of a naturally occurring basic follicle-stimulating hormone (FSH) charge isoform obtained after high-resolution chromatofocusing of human anterior pituitary glycoprotein extracts. Coincubation of increasing amounts of this isoform with a highly purified human pituitary FSH preparation or with recombinant human FSH at doses equivalent to their corresponding ED50 for estradiol and tissue-type plasminogen activator (tPA) production, inhibited FSH-induced estrogen production and tPA enzyme activity by cultured rat granulosa cells in a dose-dependent manner. These inhibitory effects were apparently exerted at steps following 3',5'-cyclic adenosine monophosphate (cAMP) formation and did not involve activation of the protein kinase C pathway since: (a) at low doses, this basic FSH isoform moderately increased FSH-induced cAMP production by cultured rat granulosa cells; (b) coincubation of the antagonist isoform with dibutyryl cAMP completely inhibited the effects of this cAMP analog on estrogen and tPA production; (c) the isoform was able to stimulate production of cAMP in a human fetal cell line expressing the recombinant human FSH receptor, and (d) the inhibitory effects of the isoform were not affected by staurosporine, a protein kinase C inhibitor. The effects of this isoform upon dibutyryl cAMP-induced estrogen and tPA production were blocked by the addition of a highly specific antibody directed against human FSH, further demonstrating that the antagonistic effects observed were due to FSH-like molecules. In contrast to the inhibitory effects exhibited by this basic FSH isoform, a more acidic FSH charge variant consistently acted as an agonist of pituitary and recombinant FSH on both estrogen production and induction of tPA enzyme activity. These results indicate that the anterior pituitary gland normally produces FSH isoforms which act as either agonists or antagonists of FSH at the target cell level.

Androgens↗
PubMed2004

Polymorphisms in human soluble epoxide hydrolase: effects on enzyme activity, enzyme stability, and quaternary structure.

Human soluble epoxide hydrolase (hsEH) has been shown to play a role in regulating blood pressure and inflammation. HsEH consists of an N-terminal phosphatase and a C-terminal epoxide hydrolase domain. In the present study, we examined the effects of polymorphisms in the hsEH gene on phosphatase activity, enzyme stability, and protein quaternary structure. The results showed that mutants Lys55Arg, Arg103Cys, Cys154Tyr, Arg287Gln, and the Arg103Cys/Arg287Gln (double mutant) have significantly lower phosphatase activity compared to the most frequent allele (MFA) of hsEH. In addition, the Lys55Arg, Arg103Cys, Cys154Tyr, Arg287Gln, and the double mutant have significantly lower kcat/Km values. The stabilities at 37 degrees C of purified Arg287Gln and Arg103Cys/Arg287Gln mutants were also significantly reduced compared to the MFA. HPLC size-exclusion studies showed that the MFA exists predominantly as a dimer. However, the Arg287Gln and Arg103Cys/Arg287Gln mutants show increased concentration of the monomer. We conclude that the Arg287Gln polymorphism disrupts putative intra- and inter-monomeric salt-bridges responsible for dimerization.

Amino Acid Substitution↗
PubMed2002

The ADP-ribosylating mosquitocidal toxin from Bacillus sphaericus: proteolytic activation, enzyme activity, and cytotoxic effects.

The mosquitocidal toxin (MTX) from Bacillus sphaericus SSII-1 is a approximately 97-kDa protein sharing sequence homology within the N terminus with the catalytic domains of various bacterial ADP-ribosyltransferases. Here we studied the proteolytic activation of the ADP-ribosyltransferase activity of MTX. Chymotrypsin treatment of the 97-kDa MTX holotoxin (MTX(30-870)) results in a 70-kDa putative binding component (MTX(265-870)) and a 27-kDa enzyme component (MTX(30-264)), possessing ADP-ribosyltransferase activity. Chymotryptic cleavage of an N-terminal 32-kDa fragment of MTX (MTX(30-308)) also yields MTX(30-264), but the resulting ADP-ribosyltransferase activity is much greater than that of the processed MTX(30-870). Kinetic studies revealed a K(m) NAD value of 45 microm for the processed 32-kDa MTX fragment, and a K(m) NAD value of 1300 microm for the processed holotoxin. Moreover, the k(cat) value for the activated MTX(30-308) fragment was about 10-fold higher than that for the activated holotoxin (MTX(30-870)). Precipitation analysis showed that the 70-kDa proteolytic fragment of MTX remains noncovalently bound to the N-terminal 27-kDa fragment, thereby inhibiting ADP-ribosyltransferase and NAD glycohydrolase activities. Glu(197) of MTX(30-264) was identified as the "catalytic" glutamate that is conserved in all ADP-ribosyltransferases. Whereas mutated MTX(30-264)E197Q has neither ADP-ribosyltransferase nor NAD glycohydrolase activity, mutated MTX(30-264)E195Q possesses glycohydrolase activity but not transferase activity. Transfection of HeLa cells with a vector encoding a fusion protein of MTX(30-264) with a green fluorescent protein led to cytotoxic effects characterized by cell rounding and formation of filopodia-like protrusions. These cytotoxic effects were not observed with the catalytically inactive MTX(30-264)E197Q mutant, indicating that the MTX enzyme activity is essential for the cytotoxicity in mammalian cells.

Adenosine Diphosphate Ribose↗
PubMed1993

Enzyme activation for activator and enzyme activity measurement.

A new sensing principle of enzyme activation is demonstrated for the determination of glycogen phosphorylase b and its allosteric effector AMP. As the indicator of the phosphorylase catalysed glycogen phosphorolysis, glucose-1-phosphate formation has been detected with an enzyme sequence comprising coentrapped alkaline phosphatase, mutarotase and glucose oxidase on a hydrogen peroxide indicating electrode. The optimized three-enzyme sensor was useful for the determination of 0.005-0.2 U.ml-1 glycogen phosphorylase a and b. A biosensor for AMP and inorganic phosphate has been developed by coupling glycogen entrapped phosphorylases to the three-enzyme indicator membrane. The measurement of AMP is based on the modulation of the phosphorylase b catalysed glycogen phosphorylating activity. The proposed sensor responds to AMP between 5 and 150 microM. The calibration graph of the reagentless phosphate sensor is linear between 0.05 and 1 mM.

Adenosine Monophosphate↗
PubMed1989

Activation mechanism of erythrocyte cathepsin E. evidence for the occurrence of the membrane-associated active enzyme.

Activation of the erythrocyte cathepsin E located on the cytoplasmic surface of the membrane in a latent form was studied in stripped inside-out membrane vesicles prepared from human erythrocyte membranes. Incubation of the vesicles at 40 degrees C at pH 4 resulted in increased degradation of the membrane proteins, especially band 3. This proteolysis was selectively inhibited by the inclusion of pepstatin (isovaleryl-Val-Val-statyl-Ala-statine) or H 297 [Pro-Thr-Glu-Phe(CH2-NH)Nle-Arg-Leu] in the incubation mixtures, indicating that cathepsin E, as the only aspartic proteinase in erythrocytes, is responsible for the proteolysis. Two potential active-site-directed inhibitors of aspartic proteinases, pepstatin and H 297, were used to prove the occurrence of the membrane-associated active enzyme. To minimize potential errors arising from non-specific binding, the concentrations of the inhibitors used in the binding assay (pepstatin, 5 x 10(-8) M; H 297, 1 x 10(-5) M) were determined by calibration for purified and membrane-associated cathepsin E. The inhibition of the membrane-associated cathepsin E by each inhibitor, which showed the binding of the inhibitor to the activated enzyme, was temperature- and time-dependent. The binding of each inhibitor to the enzyme on the exposed surface of the membrane at pH 4 was highly specific, saturable, and reversible. The present study thus provides the first evidence that cathepsin E tightly bound to the membrane is converted to the active enzyme in the membrane-associated form, and suggests that this enzyme may be responsible for the degradation of band 3.

Biotransformation↗
PubMed1976

Effects of chronic hypoxia and dietary restriction on myocardial enzyme activities.

Enzyme activities were measured in homogenates of left and right ventricles of guinea pigs after 14 and 28 days' exposure to 400 mmHg barometric pressure. All animals developed anorexia and right ventricular hypertrophy. Two control groups of animals were used, one free fed and the other restricted to the amount of food chosen by the hypobaric group. The factorial design of the experiment allowed some distinction between the effects of anorexia, hypertrophy, and hypoxia. Dietary restriction was associated with a decrease in glycogen phosphorylase, hexokinase, and succinate dehydrogenase activity and an increase in the M-subunits of lactate dehydrogenase. Myocardial hypertrophy was associated with an increase in the activity of the enzymes of the glycolytic pathway down as far as phosphoglycerate kinase and an increase in the M-subunits of lactate dehydrogenase. Chronic hypoxia seemed specifically to be associated with an increase in the H-subunits of lactate dehydrogenase and possibly a slight transient increase in succinate dehydrogenase activity. Mixing studies indicated that changes in enzyme activities were likely to be due to changes in enzyme concentrations.

Acclimatization↗
PubMed1988

Renal enzyme activities in experimental ochratoxin A-induced porcine nephropathy: diagnostic potential of phosphoenolpyruvate carboxykinase and gamma-glutamyl transpeptidase activity.

Enzyme activities have been measured in needle biopsies from kidneys of pigs fed 1 ppm or 0.2 ppm of ochratoxin A for 1-5 wks. After feeding 1 ppm toxin for 1 wk, the activity of cytosolic phosphoenolpyruvate carboxykinase (PEPCK) was decreased by 40% and remained inhibited until the termination of the experiment (5 wk). The activity of gamma-glutamyl transpeptidase, a brush-border enzyme found in the proximal tubules, was reduced to a similar degree and remained inhibited. The activities of hexokinase, a cytosolic enzyme of general distribution in the nephron, and phosphate-dependent glutaminase, a distal tubule enzyme, were not affected. The biopsy results were confirmed by measurements in renal slices taken at the termination of the experiment, except that biopsy samples showed more variation in enzyme activity and a lower PEPCK activity. A guinea pig antibody against the cytosolic form of PEPCK was used to demonstrate that the mitochondrial form of the enzyme, which accounts for a considerable part of the total cellular activity, was not affected by ochratoxin A. When mitochondrial PEPCK activity present in the cytosolic fraction was accounted for, ochratoxin A was found to reduce PEPCK activity by 70-80%. The increase of ochratoxin A exposure from zero through 0.2 ppm to 1 ppm, which resulted in dose-dependent activity decrease of PEPCK and gamma-glutamyl transpeptidase, was accompanied by dose-dependent decrease of renal function, as measured by a reduction of maximal tubular excretion of para-aminohippurate per clearance of inulin (TmPAH/CIn) and an increase in glucose excretion. This suggest that these enzymes are sensitive indicators of ochratoxin A-induced porcine nephropathy. Assuming that porcine nephropathy represents a valid model of endemic (Balkan) nephropathy in humans, the measurement of cytosolic PEPCK and gamma-glutamyl transpeptidase activity in the kidney could be a sensitive test for ochratoxin A-induced disease in humans.

Animals↗
PubMed1987

Kinetics of substrate reaction during irreversible modification of enzyme activity for enzymes involving two substrates.

Kinetic equations for the substrate reaction during simultaneous irreversible inhibition of enzyme activity for enzymes involving two substrates have been derived. It has been shown that the method proposed previously (Tsou, Acta Biochim, Biophys. Sinica 5, 398-417, 1965) for the determination of the apparent inhibition rate constants in the cases of single substrate enzymes can also be used in the present situation. Moreover, the criteria proposed to distinguish between different substrate competition types and to detect the formation of a reversible enzyme-inhibitor complex prior to the irreversible inhibition step also apply. Methods for the estimation of the microscopic rate constants have been proposed and it has been shown that irreversible inhibition kinetics can be used to distinguish between different mechanisms for substrate binding sequences.

Binding Sites↗
PubMed1979

Ethanol consumption and hepatic enzyme activity.

Enzyme activity and ethanol consumption were measured in an F2 generation derived from the C57BL and C3H inbred mouse strains. A significant correlation (0.25) was found between alcohol dehydrogenase activity and ethanol acceptance in the F2 generation. Mass selection from a genetically heterogenous mouse stock, HS/Ibg, has yielded high ethanol acceptance (HEA) and low ethanol acceptance (LEA) lines of mice. The mean ethanol acceptance scores for the fifth generation of these lines are 1.008 and 0.606, respectively. The total liver alcohol dehydrogenase activity was found to be 24% higher in the HEA line than in the LEA line after five generations of selective breeding. No association between cytosolic aldehyde dehydrogenase activity and ethanol acceptance was found in either the F2 generation or the fifth generation of the selectively bred lines.

Alcohol Drinking↗
PubMed1993

Enzyme immunoassay of beta-hexosaminidase A and B in serum: carrier detection of GM2-gangliosidoses, and equivalence of enzyme activity and enzyme protein reactivity.

beta-Hexosaminidase (Hex; EC 3.2.1.52) isoenzymes A and B were analyzed in sera from a control group of 22 apparently healthy subjects, 13 obligate carriers of Tay-Sachs disease (TSD), 10 obligate carriers of Sandhoff disease (SHD), and 4 affected TSD patients by enzyme immunoassay methods based on enzyme activity. No Hex A activity was detected in the sera of patients with TSD. The activities of Hex A in the obligate carriers of TSD and SHD tended to be lower (nonsignificantly) than in the control group. Hex B activities tended to be higher in TSD patients as well as in carriers of TSD, although the mean activities did not significantly differ from the corresponding mean for the control group. However, Hex B activities were decreased in the carriers of SHD in comparison with the other groups. Sera from 900 postmenopausal women, all of age 55 years, were also analyzed for Hex isoenzymes; the results indicated a carrier frequency of about 1 in 200 for both TSD and SHD. We also compared the enzyme immunoassay method based on enzyme activity with one based on the antigenic (enzyme protein) reactivity alone. Because both methods yielded similar information, we conclude that no significant amounts of inactive enzyme protein are present in the circulation.

Adolescent↗
PubMed1986

The diurnal rhythm of liver glycogen phosphorylase: correlating changes in enzyme activity and enzymic protein.

The diurnal rhythm of phosphorylase activity in mouse liver extracts was correlated with the 24 h fluctuations in phosphorylase protein. This last measurement was made using rocket immunoelectrophoresis. The peak activity of phosphorylase appeared coincident (at 18:00 h) with the greatest amount of phosphorylase protein detected. Conversely, the lowest activity measured and lowest enzymic protein content both occurred at 02:00 h. Regression analysis revealed a significant positive correlation between enzyme activity and protein. Thus changes in the cellular concentration of this enzyme are implicated in the diurnal rhythm of liver glycogen.

Animals↗
PubMed1985

Solvent structure and enzyme activity.

Enzymes are fluctuating particles in thermal equilibrium with their solvent environment. A variety of models of enzyme action have postulated selective excitation of enzyme vibrational modes or triggering of correlated motion of catalytic groups through collisions with solvent particles as the basis of catalytic activity. Solvent composition and structure are expected to influence such interactions. Solutes such as p-dioxane, t-butanol, and tetraalkylammonium chlorides are known to be strong perturbants of the structure of water. However, when the kinetic parameters of two enzymes, carboxypeptidase A and alpha-chymotrypsin, were examined carefully in aqueous mixtures containing these solutes, no significant influence of solvent structure or mass composition on the catalytic rate constant was found. The results indicate, furthermore, that, within the low viscosity limit, fluctuations in enzyme structure that are responsible for activated processes in the catalytically rate limiting step appear not to be significantly influenced by dynamic processes in the bulk solvent.

Binding Sites↗
PubMed1976

Enzymic activity at interfaces. II. Enzymic activity of microsomal nuclease and bovine pancreatic ribonuclease at the air/water interface.

The adsorption isotherms and the spreading tendency of microsomal nuclease (nucleate 3'-oligonucleotidohydrolase, EC 3.1.4.7) and bovine pancreatic ribonuclease (ribonucleate 3'-pyrimidino-oligonucleotidohydrolase, EC 3.1.4.22) in the presence of isopropyl alcohol as spreading agent have been determined using enzymes radioactively labelled by acetylation. In parallel, the concentration-surface pressure relations have been established. The enzymic activity of microsomal nuclease spread from isopropyl alcohol containing aqueous solutions was only a few percent of its activity in bulk, while the activity of the adsorbed enzyme was only slightly reduced. Adsorbed monolayers of RNAase were almost inactivated, while the spread monolayers in the presence of isopropyl alcohol became reactivated after exposure to the substrate for several hours. The exposure time for the reactivation decreases with increasing surface concentration.

Air↗