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M Hui

Publications and source records attributed to M Hui.

At least 37 records · Page 2Linked to original sources
PubMed1993

Changes in cell adhesion and cell proliferation are associated with expression of tissue non-specific alkaline phosphatase.

Tissue non-specific alkaline phosphatase is a membrane-bound glycoprotein enzyme which is characterized by its phosphohydrolytic, protein phosphatase, and phosphotransferase activities. This enzyme is distributed virtually in all mammalian tissues, particularly during embryonic development. Its expression is stage-specific and can be demonstrated in the developing embryo as early as the 2-cell stage. It has been suggested that tissue non-specific alkaline phosphatase might play a role in tissue formation. In the study reported here, a gene-transfer approach was employed to investigate possible roles for this enzyme by inserting the cDNA for rat tissue non-specific alkaline phosphatase into CHO and LLC-PK1 cells. Permanently transfected cell-lines expressing varying levels of alkaline phosphatase were established. The data showed that functional enzyme was expressed in the transfected cells. Cell spreading and attachment were enhanced in transfected CHO cells expressing high levels of tissue non-specific alkaline phosphatase but not in the LLC-PK1 cells. Further, in CHO cells, proliferation was shown to be inversely proportional to the level of the tissue non-specific alkaline phosphatase expression. Homotypic cell association was demonstrated in both alkaline phosphatase-positive and alkaline phosphatase-negative cells in both CHO and LLC-PK1 cell-lines. Taken together, these findings suggest that in addition to a role in mineralization of bone, tissue non-specific alkaline phosphatase might also play a role in other cell activities, including those related to differentiation, such as cell-cell or cell-substrate interaction and proliferation.

Alkaline Phosphatase↗
PubMed1993

Two cytosolic puromycin-sensitive aminopeptidase isozymes in chicken brain: molecular homology to brain-specific 14-3-3 protein.

Two puromycin-sensitive aminopeptidase isozymes (PSA-I and PSA-II) were isolated from chicken brain cytosol by ammonium sulfate fractionation followed by column chromatography on Cellex D and AH-Sepharose 4B and separated on Bio-Gel HTP. Each was purified to homogeneity on Sephadex G-200, Arg-Tyr-AH-Sepharose, Bio-Gel HTP, and preparative gel electrophoresis. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, PSA-I appeared to be a monomer with a molecular mass of 105 kDa, and PSA-II to be composed of two subunits of 25 kDa and 100 kDa. The tryptic maps of 100 kDa and 105 kDa protein in HPLC are different in peak frequency, height, and composition. The internal peptide sequence of PSA-I has a considerable homology to PSA-II. Both isozymes have repeated copies of common peptide segments and have no significant sequence homology to other peptidases and proteinases. These thio and Co(2+)-activated isozymes have a neutral pH optimum and are inhibited by puromycin and bestatin. PSA-II is more sensitive to trypsin and heat treatment, has a lower Km to Met-enkephalin, and is more active on Arg BNA and Pro BNA. Our results suggest that PSA-I and PSA-II derive from translation of two RNAs of a new gene family related to the brain-specific 14-3-3 protein.

14-3-3 Proteins↗
PubMed1990

Cellular localization of puromycin-sensitive aminopeptidase isozymes.

We developed monoclonal antibodies (mAbs) against two isozymes of a cytosolic puromycin-sensitive aminopeptidase (PSA-I and PSA-II) purified from chicken brain. The isozymes could be distinguished using Ouchterlony double-immunodiffusion and Western immunoblot. Their distribution in neuronal and glial cells as visualized by indirect immunofluorescence with these mAbs was found to differ: PSA-I was confined mostly to glial lysosomes; PSA-II showed fibrillar distribution in both types of nerve cells, but in disparate patterns. These results and our findings of peptide structural differences suggest that the two PSA isozymes are expressed differently in the nervous system.

Aminopeptidases↗
PubMed1990

[Radioimmunoassay of arginine vasopressin in human plasma].

A sensitive radioimmunoassay for human plasma arginine vasopressin was established. 125I-sAVP (1369mCi/mg) was first produced by the Iodogen method and could be used for up to one month in -25 degrees C storage. The sensitivity was 0.15 pg/tube. The sensitivity of the assay was 0.60 pg/ml, with a range of 0.6-11.0 pg/ml. The acetone-ethanol petroleum method was used to extract vasopressin from plasma samples, with a recovery rate of 75.6%. The intra- and inter-assay coefficients of variation were 9.8% and 16.8% respectively. Plasma vasopressin extraction was proved to be indispensible to the assay by virtue of its ability to minimize plasma protein interference. The physiological fluctuation of human plasma vasopressin with and without water intake was shown to be significant between normal adults and patients with neurogenic diabetes insipidus.

Arginine Vasopressin↗
PubMed1988

Aminothiols: synthesis and effect on chicken brain aminopeptidases.

An amino acid derivative, leucinethiol, was reported to be a strong inhibitor of aminopeptidase activity. In order to obtain selective inhibitors of various brain aminopeptidases, we tested the inhibition by amino acid analogs of brain aminopeptidase activity. In particular, we synthesized the trifluoroacetyl derivatives of phenylalaninol, tyrosinol, and leucinol; leucinethiol; and phenylalaninethiol and measured their effect on soluble puromycin-sensitive aminopeptidase S1 and SII purified in our laboratory. Two of the compounds, L-bis (1-thio-2-amino-4-methylpentane) dihydrochloride (TAMP) and L-bis (1-thio-2-amino-3-phenylpropane) dihydrochloride (TAPP), caused significant inhibition.

Amphetamines↗
PubMed1987

Effect of several amino acid phosphonates and related compounds on rat brain aminopeptidases.

N-Terminal sodium phosphonate derivatives Na3O3PCH2CONHR (R-Leu, Phe, or Tyr) and Na3O3PCH2CONHR-R (R-R = Leu-Phe, Phe-Leu, Phe-Phe, and Phe-Tyr) were synthesized. All showed no activity toward a soluble rat brain aminopeptidase. We could not prepare the corresponding N-2-phosphono-2,2-diphenylacetyl compounds (Na3O3PC(C6H5)2CONHR) by the same Arbusov reaction. Little or no inhibition was obtained with the N-(2-hydroxy-2,2-diphenylacetyl derivatives HOC(C6H5)2CONHR (R = Leu, Phe, Trp, or Tyr). The best inhibitory responses were given by the N-(2-halogeno-2,2-diphenylacetyl mono- and dipeptides (Br/Cl)C(C6H5)2CONH Phe and (Br/Cl)C(C6H5)2CONHR-R (R-R = Leu,Leu, Leu-Phe, Phe-Gly, Phe-Leu, or Phe-Phe), respectively.

Amino Acids↗
PubMed1986

Separation and purification of individual neurofilament proteins by reverse-phase high-performance liquid chromatography.

A reverse-phase HPLC method was developed to separate individual neurofilament proteins (210,000, 160,000 and 70,000 Da) from the glial fibrillary acid protein. It is useful for analytical or preparative methods, with yields higher than 80%. The method represents improvement over previous methods in speed, efficiency, and purity. Combining this HPLC method with the conventional chromatographic method on DEAE-cellulose, highly purified individual neurofilament proteins can be obtained in large scale.

Animals↗
PubMed1986

Effect of several amino acid phosphonates and other compounds on rat brain and kidney peptidases.

A series of N-terminal phosphonate derivatives, H2O3PCHPhNHR (R = Leu, Phe, Trp, and/or Tyr), were synthesized with the aim of mimicking phosphoramidon, a potent inhibitor of enkephalinase, while avoiding the lability of the scissile P-N bond. All of the N-phosphonobenzyl derivatives of the amino acids, including the substituted succinylhydrazobenzophenone compounds, were inactive toward rat brain aminopeptidase and rat kidney carboxypeptidase. The N-monobenzylphosphonobenzyl derivatives, PhCH2OPO(OH)CHPhNHR, of individual amino acids and several of the N-phosphonobenzyl dipeptides showed inhibition in the micromolar range toward the soluble exopeptidase but were inactive with both the brain and kidney endopeptidase.

Aminopeptidases↗
PubMed1985

An opiate receptor-associated aminopeptidase that degrades enkephalins.

During the purification of opiate receptor by affinity chromatography on wheat germ agglutinin-agarose, an aminopeptidase is coeluted with the receptor. Virtually all of both the enzyme and the receptor is retained on the hydroxylapatite column. The aminopeptidase functions optimally at neutral pH and is activated by Mn2+. The enzyme is sensitive to dithiothreitol, is inhibited by amastatin and bestatin, and is insensitive to puromycin. The enzyme seems to be linked to the receptor, since its activity is enhanced by D-Ala2-Met-enkephalinamide or naltrexone. The properties of this aminopeptidase indicate that it is distinct from neutral arylamidase, leucine-aminopeptidase, aminopeptidases A and B, brain acidic aminopeptidase, and the membrane aminoenkephalinase that we purified recently (4).

Aminopeptidases↗
PubMed1983

Effect of various compounds on enkephalin hydrolysis by an aminopeptidase from the thermophiles Thermomonospora fusca ATCC 27730 and Thermus thermophilus ATCC 27634.

The microbial peptides amastatin and bestatin as well as several dipeptide analogues of the latter exerted little or no inhibitory effect on enkephalin hydrolysis by an aminopeptidase purified from the thermophiles Thermomonospora fusca, ATCC 27730 (Tf) and Thermus thermophilus, ATCC 27634 (Tt). The enzyme catalyzes the cleavage of the tyrosyl-glycyl bond of leucine- and methionine-enkephalin. Intermediate compounds having the same amino acid sequence as the parent substrate disclosed that the residual tetrapeptide can be further degraded to its constituent parts. Each preparation also hydrolyzes to varying extents neutral dipeptides, tripeptides, tetrapeptides, can be further degraded to its constituent parts. Each preparation also hydrolyzes to varying extents neutral dipeptides, tripeptides, tetrapeptides, and larger molecules containing the Met-enkephalin sequence. The Tf enzyme has a pH optimum of 7.5, Km of 667 microM and Vmax of 92 nmol/min/mg of protein; the Tt enzyme, with a pH optimum of 7.2 has a Km of 400 microM and Vmax of 33 nmol/min/mg of protein. Activated by dithiothreitol (DTT) and inactivated by p-chloro- and p-hydroxymercuribenzoate, both are sulfhydryl enzymes. The activity lost by hydrolysis against EDTA can be restored, wholly or in part, by Co+2, Mg+2, and Mn+2; ions with an inhibitory effect were A1+3, Cd+2, Cu+2, Hg+2, and Zn+2. The enzymes are not glycoproteins since they pass unretained through a Con A-Sepharose column.

Actinomycetales↗
PubMed1983

Effect of bestatin analogues and other compounds on enkephalin hydrolysis by an aminopeptidase from the mesophiles pseudomonas sp ATCC 11299A and chromobacterium violaceum ATCC 12540.

In our studies on newly synthesized compounds for their potential analgesic effect, we decided for purposes of convenience and economy to investigate non-mammalian sources for the presence of enkephalin degrading enzymes. An aminopeptidase that catalyzes the hydrolysis of the tyrosylglycyl bond of leucine- and methionine enkephalin was purified from the mesophiles Pseudomonas sp ATCC 11299a (Ps) and Chromobacterium violaceum ATCC 12540 (Cv). Each preparation also hydrolyzed to varying extents neutral dipeptides, tripeptides, tetrapeptides and amino acid beta-naphthylamides. The Ps enzyme has a pH optimum of 6.8, Km of 80 microM and a Vmax of 6.7 nmoles/min/mg of protein. The Cv enzyme has a pH optimum of 6.8-7.2, Km of 111 microM and a Vmax of 42 nmoles/min/mg of protein. Both are sulfhydryl enzymes since they are activated by dithiothreitol (DTT) and inactivated by p-chloro- and p-hydroxymercuribenzoate. They are not glycoproteins since they pass unretained through a Con A-Sepharose column. The activity lost by dialysis against EDTA can be restored, wholly or in part, by Co+2, Mg+2, Mn+2 and Ni+2; ions exerting an inhibitory effect were A1+3, Cd+2, Cu+2, Hg+2 and Zn+2. From a range of organic compounds, the greatest inhibition was elicited by the microbial peptides amastatin and bestatin. Several dipeptide analogues of bestatin, synthesized from DL-threo-2-amino-3-hydroxy-3-phenylpropanoic acid (AHPP) as the N-terminal residue in order to define the stereospecific requirements of the alpha, beta-functional groups for maximal activity, were not as active as the parent compound.

Aminopeptidases↗
PubMed1981

Attempts at induction of phenylalanine hydroxylase in thermophilic bacteria and induction of thermophily in mesophiles.

Some moderate and extreme thermophilic bacteria grew well on media other than the recommended basic media. Attempts to induce phenylalanine hydroxylase (Phe H) in the various thermophiles as well as mild thermophily in the mesophiles Pseudomonas sp ATCC 11299a and Chromobacterium violaceum ATCC 12540 were unsuccessful. Evidence is presented indicating that the enzyme in the latter two organisms may be membrane bound. The level of Phe H activity induced was not always consistent with the level of the inducer phenylalanine (Phe) in the growth medium.

Bacteria↗
PubMed1980

The gastroplasty tube and its role in reflux control: an experimental and clinical study.

The gastroplasty tube has been used in the control of reflux since it was originally described by Collis in 1961. Several variations of the procedure have been reported indicating a low frequency of anatomic recurrence but a high frequency of reflux. Two forms of gastroplasty procedure are used: partial fundoplication in which gastric fundus incompletely wraps the gastroplasty and high pressure zone, and total fundoplication in which a circumferential wrap is constructed. The authors conducted a clinical review, using the patient's history, radiology and manometry, of 135 patients with partial fundoplication gastroplasty (PFG) and 250 patients with total fundoplication gastroplasty (TFG). In both groups the anatomic recurrence rate was low; however, with PFG the frequency of reflux was 44.6% and 25.7% of patients had notable symptoms. With TFG no patient had reflux. The response of the gastroplasty tube to meal-induced gastrin release and to neurogenic stimulation was tested. Basal tube pressure was low and showed no response to gastrin release and no augmented neurogenic response. It was concluded that the gastroplasty tube did not have intrinsic properties of value in controlling reflux and that reflux control depended upon the method of fundoplication. The role of the gastroplasty tube is in preventing anatomic recurrence.

Eating↗
PubMed1979

Purification and covalent coupling of calf brain prolidase.

We have investigated methods of stabilizing prolidase by chemical modification and covalent coupling to various supports, for use in protein hydrolysis and possible use in enzyme replacement therapy. Purified acetone powder of calf brain prolidase was further purified by gel filtration on Sephadex G-200 and chromatography on DEAE-Sephadex A25. Polyacrylamide gel electrophoresis showed that the number of bands was reduced from 11 to 2. Since yields were low, the purified (NH4)2SO4 fraction was used in all experiments. Thiolation of the enzyme reduced the amount of protein coupled to AH- or CH-Sepharose 4B. Activities were highest when the protein was linked through its carboxyl groups. The coupled enzyme showed much greater thermal stability than its free counterpart. Of the bound preparations, the thiolated was less stable than the untreated. Untreated and thiolated enzymes bound to either matrix showed higher activity at low pH and less at high pH than the free material. Thiolation shifted the pH maximum from 6.8 to 7.5. The free thiolated enzyme and that bound to activated SH-Sepharose 4B showed greater thermal stability and a broader pH range of optimal activity than the bound untreated enzyme. These results show that prolidase can be immobilized by coupling to an insoluble matrix through various types of covalent bonds with retention of activity and increased stability.

Animals↗
PubMed1979

V. Efforts at stabilization of rat liver phenylalanine hydroxylase.

The best from a series of matrices for the covalent coupling of rat liver phenylalanine (Phe H) was activated thiol-Sepharose 4B. An average of 0.38 mumoles of enzyme thiol was coupled per mumole of matrix thiol, representing 21 mg of protein per g of carrier. After thiolation with N-acetylhomocysteine thiolactone the enzyme, bound to the same matrix, was thermally more stable with a broad pH range of optimal activity. Thiolation with S-acetylmercaptosuccinic anhydride markedly reduced hydroxylase activity whereas succinylation with succinic anhydride had little or no effect. Treatment of the thiolated enzyme with various oxidants to form disulfide bridges did not increase the thermal stability. Efforts to improve stability by formation of new linkages while the enzyme was still bound to the matrix were unsuccessful. The untreated or thiolated enzyme was inactivated upon reaction with glutaraldehyde.

Animals↗