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Biomedical subjects

B Yu

Publications and source records attributed to B Yu.

At least 199 records · Page 11Linked to original sources
PubMed1993

Differential effects of calyculin A and okadaic acid on the glucose-induced regulation of glycogen synthase and phosphorylase activities in cultured hepatocytes.

The effects of the phosphatase inhibitors calyculin A and okadaic acid were investigated to determine the roles of protein phosphatases type 1 and 2A in the regulation of the activities of glycogen synthase and phosphorylase by glucose in a primary culture of hepatocytes. Glycogen synthesis, as measured by the incorporation of labelled glucose into glycogen, was inhibited in a dose-dependent manner by calyculin A (IC50 = 2.2 nM) and okadaic acid with (IC50 = 14 nM). Glucose-induced activation of glycogen synthase was inhibited by calyculin A and okadaic acid with IC50 values of 3.7 nM and 90 nM, respectively. Phosphorylase was simultaneously activated by these inhibitors with calyculin A again being more active (P < 0.001) than okadaic acid. The differing potencies (P < 0.001) of these inhibitors on the activities of glycogen synthase and phosphorylase were also observed with varying concentrations of glucose (5.6-60 mM) in the medium and at different incubation periods upto 120 min. It has been previously shown that both inhibitors inhibit protein phosphatase-2A with equal potency and calyculin A is a more potent inhibitor of protein phosphatase-1 than okadaic acid. Heat- and proteinase-treated cytosolic fractions from hepatocytes incubated with calyculin A and okadaic acid showed similar differential inhibitory activities towards purified types 1 and 2-A protein phosphatases. Hence, these data provide further evidence that protein phosphatase type-1 plays a major role in the control of glycogen synthesis by regulating the activities of glycogen synthase and phosphorylase.

Animals↗
PubMed1993

2-Hydroxypropyl-beta-cyclodextrin enhances phorbol ester effects on glucose transport and/or protein kinase C-beta translocation to the plasma membrane in rat adipocytes and soleus muscles.

In rat adipocytes and soleus muscles, 2-hydroxypropyl-beta-cyclodextrin (CD) was found to have a relatively small or no effect on basal or insulin-stimulated hexose uptake, but markedly enhanced hexose uptake effects of phorbol esters and/or diacylglycerol. In rat adipocytes, the CD-induced enhancement of hexose uptake during concurrent phorbol ester treatment was not associated with an increase in GLUT4 glucose transporter translocation to the plasma membrane, which was stimulated comparably by insulin and phorbol esters. Moreover, CD appeared to activate or facilitate the activation of glucose transporters subsequent to their translocation to the plasma membrane during ongoing phorbol ester treatment. In rat adipocytes, CD also enhanced the translocation of protein kinase C (PKC)-beta to the plasma membrane during the action of phorbol esters, which alone had little or no effect on this specific PKC translocation. Although it is uncertain how CD alters the function of plasma membranes to enhance the translocation of PKC-beta to, and the activation of glucose transporters within, this subcellular fraction during phorbol ester treatment, our findings provide direct support for a two-step model in the activation of glucose transport. In addition, it seems clear that, at least in some cell types, simple phorbol ester treatment does not necessarily serve as a ubiquitous activator of all activable PKC pools and all potential PKC-mediated responses.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1993

Changes in the structure and catalytic activities of the bovine pituitary multicatalytic proteinase complex following dialysis.

The multicatalytic proteinase complex (proteasome) contains at least four distinct active sites catalyzing the degradation of selected chromogenic substrates (trypsin-like, chymotrypsin-like, and peptidylglutamyl peptide hydrolyzing activities) and proteins such as beta-casein. Oxidized insulin B chain was recently proposed as a model substrate for protein degradation by the multicatalytic proteinase complex (Dick, L. R., Moomaw, C. R., DeMartino, G. N., and Slaughter, C. A. (1991) Biochemistry 30, 2725-2734). We studied the dialysis-induced activation of the hydrolysis of oxidized insulin B chain by this enzyme. Removal of EDTA from purified preparations of bovine pituitary multicatalytic proteinase complex by dialysis against Tris-HCl buffers led to marked changes in the catalytic properties and structure of the enzyme. Dialysis produced a time-dependent activation of oxidized insulin B chain hydrolysis with predominant cleavage at the Glu13-Ala14 bond. A new chromogenic assay was developed for measurement of this activity. Activation was accompanied by a virtually total inactivation of the chymotrypsin-like, trypsin-like, and peptidylglutamyl peptide hydrolyzing activities. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a loss of the 24-kDa subunit and the appearance of a new band at 21 kDa. Amino-terminal amino acid analysis established that the 21-kDa band was autolytically derived from the 24-kDa subunit. Evidence for partial dissociation and/or aggregation indicated that autolysis destabilizes the complex. By altering the profile of catalytic activities of the multicatalytic proteinase complex, autolysis may serve as a mechanism for regulation of this macromolecule.

Amino Acid Sequence↗
PubMed1993

The lux autoinducer regulates the production of exoenzyme virulence determinants in Erwinia carotovora and Pseudomonas aeruginosa.

Erwinia carotovora and Pseudomonas aeruginosa secrete exoenzymes that contribute to the pathogenesis of plant and mammalian infections respectively. E.carotovora mutants defective in synthesis of the pectinase, cellulase and protease exoenzymes were isolated and classified into two groups. Group 2 mutants were found to be defective in the production of a small freely diffusible molecule, N-3-(oxohexanoyl)-L-homoserine, lactone (HSL), and were avirulent. Addition of exogenous HSL to these group 2 mutants restores synthesis of the exoenzymes and virulence in planta. Of the exoenzymes of P.aeruginosa the metalloprotease, elastase, is an established virulence determinant. Mutants of P.aeruginosa that are defective in elastase production have been isolated and were again found to fall into two groups. Analogous to the group 2 mutants of E.carotovora, group 2 mutants of P. aeruginosa are defective in the synthesis of HSL and exogenous HSL restores elastase production. HSL has now been linked to the control of bioluminescence in Vibrio fischeri, carbapenem antibiotic production of E.carotovora and the above exoenzyme virulence determinants. This information significantly enhances our understanding of the extent and nature of pheromone mediated gene expression control in prokaryotes.

4-Butyrolactone↗
PubMed1993

A panning DLT procedure for three-dimensional videography.

The direct linear transformation (DLT) method [Abdel-Aziz and Karara, APS Symposium on Photogrammetry. American Society of Photogrammetry, Falls Church, VA (1971)] is widely used in biomechanics to obtain three-dimensional space coordinates from film and video records. This method has some major shortcomings when used to analyze events which take place over large areas. To overcome these shortcomings, a three-dimensional data collection method based on the DLT method, and making use of panning cameras, was developed. Several small single control volumes were combined to construct a large total control volume. For each single control volume, a regression equation (calibration equation) is developed to express each of the 11 DLT parameters as a function of camera orientation, so that the DLT parameters can then be estimated from arbitrary camera orientations. Once the DLT parameters are known for at least two cameras, and the associated two-dimensional film or video coordinates of the event are obtained, the desired three-dimensional space coordinates can be computed. In a laboratory test, five single control volumes (in a total control volume of 24.40 x 2.44 x 2.44 m3) were used to test the effect of the position of the single control volume on the accuracy of the computed three dimensional space coordinates. Linear and quadratic calibration equations were used to test the effect of the order of the equation on the accuracy of the computed three dimensional space coordinates. For four of the five single control volumes tested, the mean resultant errors associated with the use of the linear calibration equation were significantly larger than those associated with the use of the quadratic calibration equation. The position of the single control volume had no significant effect on the mean resultant errors in computed three dimensional coordinates when the quadratic calibration equation was used. Under the same data collection conditions, the mean resultant errors in the computed three dimensional coordinates associated with the panning and stationary DLT methods were 17 and 22 mm, respectively. The major advantages of the panning DLT method lie in the large image sizes obtained and in the ease with which the data can be collected. The method also has potential for use in a wide variety of contexts. The major shortcoming of the method is the large amount of digitizing necessary to calibrate the total control volume. Adaptations of the method to reduce the amount of digitizing required are being explored.

Biomechanical Phenomena↗
PubMed1993

Lactobacillus cells in the rabbit digestive tract and the factors affecting their distribution.

Lactobacillus fermentum was present in small numbers in the caecum and colon of only one of 16 rabbits. Studies aimed at elucidating the factors affecting the colonization of lactobacilli in rabbit gut were thus performed. These studies included investigation of the effect of gastric juice and bile salts on the viability of lactobacilli, assay of the survival rates of lactobacilli in the gastrointestinal tracts of the rabbits with or without ileum cannulation and measurement of the adhesive capability of lactobacilli to the rabbit intestinal epithelial cells. Results showed that, although some lactobacilli were resistant to the rather low pH levels of rabbit gastric juice, lack of adhesive capability may prevent them from colonizing in the intestinal tract. Therefore, if lactobacilli are to be used as probiotics for rabbit, factors that affect their viability and ability to colonize should be considered.

Administration, Oral↗
PubMed1993

Treatment of herpes zoster: recombinant alpha-2a-interferon versus acyclovir and vitamin therapy. Clinical Study Group on Interferon.

The efficacy of r-interferon alpha 2a (IFM) versus acyclovir (ACV) and vitamin therapy in the treatment of herpes zoster is reported. A total of 305 patients were randomly divided into 3 groups. One million units of IFN were administered i.n. once a day for 6 days in 223 cases, oral ACV 200 mg five times daily for 7 days in 34 cases, and vitamin B12, B1 and B2 therapy at conventional doses for 7-14 days in 48 cases. The results showed that both IFN and ACV could reduce pain in patients with herpes zoster and cut the total duration of symptoms, in comparison with vitamin therapy (P < 0.01). In the IFN group, 45 patients (20.2%) experienced side effects, including mild fever in 35 cases (15.7%) and a slightly depressed leukocyte count or increased serum ALT level (3 cases each). In the ACV group, one complained of discomfort in the gastroenteric tract, and another patient reported lumbodynia.

Acyclovir↗
PubMed1992

Direct evidence for protein kinase C involvement in insulin-stimulated hexose uptake.

Insulin has been reported to translocate protein kinase C (PKC) in rat adipocytes, and activation of PKC by phorbol esters is known to increase hexose uptake in these cells (1.2). To test the hypothesis that PKC may participate in insulin-stimulated hexose uptake, adipocytes were partially depleted of protein kinase C by overnight phorbol ester treatment, thereby impairing insulin effects on hexose uptake. Purified PKC was then introduced into these PKC-depleted adipocytes by electropermeabilization, and this fully restored insulin-stimulated hexose uptake. These findings provide direct evidence that PKC is required for insulin-stimulated hexose uptake.

Adipose Tissue↗
PubMed1992

3,4-dichloroisocoumarin-induced activation of the degradation of beta-casein by the bovine pituitary multicatalytic proteinase complex.

The breakdown of beta-casein (caseinolytic activity) by the bovine pituitary multicatalytic proteinase complex (MPC) is initiated by a fourth active site different from the previously described chymotrypsin-like activity (cleavage of Cbz-Gly-Gly-Leu-p-nitroanilide, where Cbz is benzyloxycarbonyl), trypsin-like activity (cleavage of Cbz-D-Ala-Leu-Arg-2-naphthylamide), and peptidylglutamyl peptide bond-hydrolyzing (PGP) activity (cleavage of Cbz-Leu-Leu-Glu-2-naphthylamide) (Yu, B., Pereira, M. E., and Wilk, S. (1991) J. Biol. Chem. 266, 17396-17400). 3,4-Dichloroisocoumarin, a serine proteinase inhibitor, stimulated the caseinolytic activity of bovine pituitary or lens MPC, 3-18-fold under conditions under which the other three catalytic activities were inactivated. Addition of hydroxylamine to the modified enzyme did not reverse the effects of the inhibitor. A form of the proteinase exhibiting only 2-4% of control chymotrypsin-like, trypsin-like, and PGP activities degraded beta-casein with no accumulation of intermediate peptides. 3,4-Dichloroisocoumarin, by reacting with the chymotrypsin-like, trypsin-like, and/or PGP-active sites, may promote a conformational change of MPC, rendering the caseinolytic active site accessible to the substrate. Once bound to the active site, beta-casein is rapidly degraded either by the caseinolytic component itself or by a cooperative interaction with catalytic centers that are not affected by the serine proteinase inhibitor. These results imply that the caseinolytic component does not belong to the class of serine proteinases. Other proteins tested were not degraded by the 3,4-dichloroisocoumarin-treated enzyme, suggesting that the conformation of beta-casein may be more adequate for degradation by the caseinolytic component.

Amino Acid Sequence↗
PubMed1992

Enzymatic changes of the bovine pituitary multicatalytic proteinase complex, induced by magnesium ions.

The effect of magnesium ions on the catalytic activities of the bovine pituitary multicatalytic proteinase complex (MPC) was studied. Mg2+ markedly stimulated the breakdown of dephosphorylated beta-casein (caseinolytic activity) and the hydrolysis of Cbz-Leu-Leu-Glu-2-naphthylamide (peptidylglutamyl peptide bond hydrolyzing activity) by a 1700-fold purified preparation of MPC. Cleavage of Cbz-D-Ala-Leu-Arg-2-naphthylamide (trypsin-like activity) was strongly inhibited and cleavage of Cbz-Gly-Gly-Leu-p-nitroanilide (chymotrypsin-like activity) was weakly inhibited. Similar results were produced when enzymatic activities in the absence of Mg2+ were measured at 52 degrees C rather than at 37 degrees C. Trace protein impurities were removed by phenyl-Sepharose chromatography. This additional chromatographic step, while not changing the specific activities of hydrolysis of the three synthetic chromogenic substrates, led to a marked activation of the breakdown of dephosphorylated beta-casein. Mg2+ was not able to further stimulate the caseinolytic activities of either the phenyl-Sepharose-treated preparation or the preparation measured at 52 degrees C. Mg2+ therefore converts a "repressed" form of MPC to an "activated" form, possibly by promoting dissociation of a protein inhibitor, and may serve as a physiological regulator of this enzyme complex.

Amino Acid Sequence↗
PubMed1992

Effects of insulin on diacylglycerol/protein kinase-C signalling and glucose transport in rat skeletal muscles in vivo and in vitro.

Insulin treatment in vivo provoked rapid dose-related increases in diacylglycerol content and/or translocation of protein kinase-C (PKC) from cytosol to membranes in rat soleus and gastrocnemius muscles. These effects were apparent with 1) insulin doses that provoked submaximal and maximal increases in glucose utilization, and 2) glucose-stimulated endogenous insulin secretion. Insulin-stimulated PKC translocation was evident when PKC was assayed by 1) histone or protamine phosphorylation after PKC purification by Mono Q column chromatography, and 2) immunoblotting for PKC beta and PKC epsilon. Dose-related effects of insulin on PKC translocation were also observed in the rat soleus in vitro, and this was associated with increased phosphorylation of 40- and 80-kilodalton proteins, which were also phosphorylated by phorbol ester treatment. A role for diacylglycerol-PKC signalling in insulin-stimulated glucose transport was suggested by studies of [3H]2-deoxyglucose ([3H]2-DOG) uptake in the rat soleus in vitro in that 1) PKC translocation and 2-DOG uptake were correlated; and 2) stimulatory effects of insulin and phorbol esters on 2-DOG uptake were apparently nonadditive.

Animals↗
PubMed1992

Effect of serum thyrotropin levels on the concentration of messenger RNA for thyroid peroxidase in the rat.

The effect of serum TSH on rat thyroid peroxidase mRNA levels was studied in order to investigate the regulation of thyroid peroxidase gene expression in vivo. A nearly full-length rat thyroid peroxidase cDNA clone was isolated from a bacteriophage cDNA library synthesized using poly A+ RNA isolated from the thyroids of propylthiouracil-treated rats. cDNA probes derived from this clone were used to study rat thyroid peroxidase mRNA levels in response to the level of serum TSH. Two major rat thyroid peroxidase mRNA bands were detected on Northern blots of total cellular RNA (at 3.2 kb and at 3.7 kb). Injection of thyroxine, which lowered the levels of serum TSH, also lowered the steady-state levels of both rat thyroid peroxidase mRNAs, whereas treatment with methimazole, which increased serum TSH, increased both rat thyroid peroxidase mRNA levels. In hypophysectomized rats 10 days postoperative, very low levels of thyroid peroxidase mRNA were observed. Injection of bovine TSH (1 IU/day) increased rat thyroid peroxidase mRNA expression, preferentially in the 3.2 kb band. These results clearly demonstrate that TSH regulates rat thyroid peroxidase mRNA levels in vivo.

Animals↗
PubMed1991

Chemical modification of the bovine pituitary multicatalytic proteinase complex by N-acetylimidazole. Reversible activation of casein hydrolysis.

The effect of N-acetylimidazole, a mild acetylating reagent, on the catalytic activities and subunit structure of the bovine pituitary multicatalytic proteinase complex (MPC) was studied. The trypsin-like activity (cleavage of Cbz-D-Ala-Leu-Arg-2-naphthylamide) and the peptidylglutamyl-peptide bond hydrolyzing (PGP) activity (cleavage of Cbz-Leu-Leu-Glu-2-naphthylamide) of MPC were rapidly inactivated by N-acetylimidazole, whereas the chymotrypsin-like activity (cleavage of Cbz-Gly-Gly-Leu-p-nitroanilide) was inactivated slowly. However, the hydrolysis of casein was markedly stimulated. Hydrolysis of casein by the acetylated enzyme generated a stable intermediate (21 kDa) which could be further degraded by native MPC. Treatment of acetylated MPC with hydroxylamine reversed the changes in trypsin-like and caseinolytic activities but did not restore the PGP activity. N-Acetylimidazole did not dissociate MPC but altered its migration on nondissociating gels presumably by acetylation of epsilon-amino groups of lysine residues. Hydroxylamine did not alter the gel electrophoretic appearance of the acetylated enzyme. These results indicate that acetylation of thiol or tyrosyl groups changes the trypsin-like and caseinolytic activities, and that amino group acetylation inhibits the PGP activity. Degradation of casein by MPC appears to be a sequential process with initial cleavage catalyzed by a component distinct from the chymotrypsin-like, trypsin-like, and PGP activities. The latter three components likely participate in the secondary proteolysis of the generated intermediates.

Amino Acid Sequence↗
PubMed1991

Distribution of endopeptidase-24.15 in rat brain nuclei using a novel fluorogenic substrate: comparison with endopeptidase-24.11.

A novel fluorogenic substrate for the neutral metalloendopeptidase-24.15 (E.C.3.4.24.15; EP-24.15) was synthesized which allowed continuous assay of the enzyme. The substrate, Glutaryl-Phe-Ala-Ala-Phe-4-methoxynaphthylamide (G-FAAF-4MN) is cleaved at the Phe-Ala bond by EP-24.15 (Km = 0.026 mM). The product, AAF-4MN is subsequently hydrolyzed to its constituent amino acids and the potent fluorophore 4MN by aminopeptidase M. This method has allowed the measurement of the specific activity EP-24.15 within microdissected nuclei of rat brain. The enzyme was found to have a relatively broad distribution within brain nuclei, and the activity ranged from 15-80 nmol 4MN/mg prot/h in all areas examined. The activity of EP-24.15 was relatively high in the medial and lateral pre-optic nuclei, where potential substrates include the dynorphin-like peptides and LHRH. The activity of EP-24.15 was compared with that of endopeptidase-24.11 (E.C.3.4.24.11, 'enkephalinase', EP-24.11), another peptide-cleaving metalloenzyme. EP-24.11 appeared to have a much more narrow distribution, with very high specific activity in basal ganglia as well as in the supraoptic and suprachiasmatic nuclei.

Amino Acid Sequence↗
PubMed1991

Antisense DNA downregulates protein kinase C isozymes (beta and alpha) and insulin-stimulated 2-deoxyglucose uptake in rat adipocytes.

Rat adipocytes were treated with antisense dimethoxytrityl pentadecadeoxynucleotides, complementary to mRNA initiation codon regions for alpha and beta isozymes of protein kinase C (PKC). This antisense treatment provoked 50-70% decreases in PKC and insulin-stimulated 2-deoxyglucose uptake, but did not inhibit insulin-stimulated diacylglycerol synthesis. Sense or nonsense oligodeoxynucleotides were without effect on PKC and 2-deoxyglucose uptake. These results suggest that: (i) PKC-alpha and PKC-beta isozymes can be specifically downregulated in rat adipocytes by antisense oligodeoxynucleotides, and (ii) insulin-stimulated glucose transport requires PKC.

Adipose Tissue↗