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Biomedical subjects

S S Wong

Publications and source records attributed to S S Wong.

At least 19 recordsLinked to original sources
PubMed1992

Transcription induction of c-Ki-ras with the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in normal and transformed liver cells.

Results from nuclear run-off assays show that exposure of hepatocytes and Reuber H35B hepatoma cells to the tumour promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), leads to enhanced transcription of c-Ki-ras gene. This increase in transcription in turn results in an accumulation of the functionally active c-Ki-ras message. The half life of c-Ki-ras message in both normal and transformed livers cells is not altered by TPA and is determined to be 3.5 hr. The induction of c-Ki-ras message is accompanied by an increase in the level of c-Ki-ras protein.

Animals↗
PubMed1992

Mechanism of differential inhibition of lactate dehydrogenase isoenzymes in the BMC LD-1 assay.

The mechanism of inhibition of lactate dehydrogenase (LD) isoenzymes by guanidinium thiocyanate (GSCN) used in the LD-1 assay developed by Boehringer Mannheim Corporation (BMC) was investigated. Michaelis-Menten inhibition kinetics for the individual isoenzymes revealed that GSCN competitively inhibited LD-1 in the presence of lactate and NAD+, but is a noncompetitive inhibitor of LD-5. LD-2 and LD-3 exhibited mixed inhibition kinetics. The inhibition constants were two- to threefold smaller for LD-5 than for LD-1. Time-dependent studies also showed that the isoenzymes underwent a different rate of inactivation by GSCN. LD-5, LD-3, and LD-2 were rapidly inactivated within 1 min under the BMC assay conditions, whereas LD-1 lost only about 20% of activity after 10 min. The presence of lactate further protects LD-1, but not other isoenzymes. Under this condition, LD-1 was not inactivated during the initial 6 min of reaction. Separate experiments demonstrated that both guanidinium and thiocyanate ions are responsible for the inactivation process that was found to be irreversible. We speculate that GSCN selectively denatures the M subunit of LD. The H subunit is less susceptible to denaturation and is further stabilized by lactate.

Guanidines↗
PubMed1992

Chemical crosslinking and the stabilization of proteins and enzymes.

The technique of chemical crosslinking has been used to enhance the stability of proteins and enzymes. In this procedure, the molecule is braced with chemical crosslinks either intramolecularly or intermolecularly to another species to reinforce its active structure. Various chemicals have been used for this purpose. The bifunctional reagents are the most prominent. These compounds are derived from group-specific reagents and may be classified into homobifunctional, heterobifunctional, and zero-length crosslinkers. Different physical and chemical characteristics have been incorporated into these chemicals. Their versatility holds great potential in preparing chemically, thermally, and mechanically stable proteins and enzymes for industrial applications.

Cross-Linking Reagents↗
PubMed1992

Expression of c-Ki-ras in developing rat liver.

1. Two major c-Ki-ras transcripts are present in rat liver throughout development. 2. Both transcripts are functional, i.e. translatable into ras protein. 3. They exhibit low levels in early foetuses and increase gradually towards term. 4. Peak levels of transcripts are detected on the fourth day of postnatal life. 5. Results from nuclear run-off assays demonstrate that the rise in level of transcripts is a result of increase in rate of transcription with the highest rate detected on the fourth day of postnatal life. 6. Western blot analysis reveals that the accumulation of c-Ki-ras protein clearly follows the pattern of changes in transcription of c-Ki-ras gene.

Animals↗
PubMed1992

Familial acne fulminans.

We report a patient of acne fulminans with arthralgia whose sister presented with the same disease at an identical age 10 years earlier. The two affected siblings in our family also had identical HLA phenotypes which further supported the role of genetic susceptibility in acne fulminans.

Acne Vulgaris↗
PubMed1992

Lichenoid eruption induced by low dose captopril.

A patient with congestive cardiac failure developed a rash following captopril treatment. The clinical and histological features were consistent with a lichenoid eruption. The rash spontaneously resolved without any treatment three months after captopril was discontinued.

Aged↗
PubMed1992

Dose-related effects of doxazosin on plasma lipids and aortic fatty streak formation in the hypercholesterolemic hamster model.

Doxazosin, an alpha 1-adrenergic inhibitor, has been shown to decrease hypertension and plasma lipids, especially total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C), thus reducing certain risk factors associated with increased incidence of cardiovascular disease. One preliminary report indicated that the decrease in LDL-C in hypercholesterolemic hamsters treated with doxazosin was associated with a reduction in fatty streak formation. However, since the effects of doxazosin on plasma lipids, aortic fatty streak development, or the relationship between the two have not been studied in a dose-dependent manner, these effects were further investigated over varying doses of doxazosin (0, 1, 5, 10, and 20 mg/kg body wt/day) during a 10-week period. Doxazosin administration was associated with a dose-dependent decrease in LDL-C of 2%, 29%, 52%, and 60%, whereas the degree of fatty streak formation was reduced 11%, 45%, 76%, and 92% compared with controls, with the first statistically significant decrease for both parameters at the 10 mg/kg dose. Significant correlations between LDL-C concentrations and fatty streak area suggest that doxazosin altered aortic lipid infiltration primarily by its effect on plasma lipids. However, the 20 mg/kg dose of doxazosin significantly decreased lesion area compared with the 10 mg/kg dose without a further effect on plasma lipid concentrations. Three animals at these higher doses demonstrated no stainable lipid inclusions while maintaining plasma lipid values similar to their cohorts. These exceptions to the lipid-lesion relationship raise the possibility of additional effects of doxazosin, which may occur independent of or in concert with lipoprotein cholesterol lowering, on lesion formation.

Adrenergic alpha-Antagonists↗
PubMed1992

Effect of hypoimmunoglobulinemia on laboratory evaluation of multiple sclerosis.

A female patient with Crohn's disease was assessed by laboratory evaluation for multiple sclerosis. Because of her hypoproteinemia, she was given an albumin infusion, which caused immunoglobulin concentrations to fall below the normal limit. Based on a cerebrospinal fluid (CSF) sample drawn after infusion, she was found to have an abnormally high IgG index and a high intrathecal IgG synthesis rate. However, clinical correlations ruled out demyelinating disease. Various equations used for the calculation were examined and found to yield false positive results with values of serum IgG below the reference range. Only the Ohman formula provided the correct prediction in this patient. Although hypo- or hyper-albuminemia have little effect on these equations, they may escalate the impact of hypoimmunoglobulinemia. Thus, interpretation of laboratory data under these conditions must be exercised with care.

Adult↗
PubMed1991

A calmodulin-binding peptide of caldesmon.

Caldesmon is a major actin-binding protein identified in smooth muscle and many non-muscle cells. It also interacts with calmodulin and a number of other acidic proteins. We have shown previously that the polypeptide stretch from Val629 to Ser666 near the C terminus contains a calmodulin binding site (Wang, C.-L. A., Wang, L.-W. C., Xu, S., Lu, R. C., Saavedra-Alanis, V., and Bryan, J. (1991) J. Biol. Chem. 266, 9166-9172). On the other hand, Bartegi et al. (Bartegi, A., Fattoum, A., Derancourt, J., and Kassab, R. (1990) J. Biol. Chem. 265, 15231-15238) reported a cyanogen bromide fragment beginning at Trp659 which is also capable of binding both calmodulin and actin. A comparison of the overlapping sequence between these two peptides suggests that this calmodulin binding site is localized in a 7-residue segment, 659Trp-Glu-Lys-Gly-Asn-Val-Phe665. We have chemically synthesized an 18-residue peptide (GS17C, from Gly651 to Ser667 with an added cysteine at the C terminus) that contains this segment. This peptide was purified by high performance liquid chromatography and labeled with fluorescent probes at the terminal cysteine residue. We found that GS17C indeed binds calmodulin in a Ca(2+)-dependent manner (Kd = 8 x 10(-7) M) and appears to compete with caldesmon. Interestingly, this synthetic peptide also co-sediments with F-actin, binding to actin being displaceable by calmodulin, as in the case of the native caldesmon. But GS17C does not have any effect on the actomyosin ATPase activity, indicating that this peptide segment does not contain the inhibitory region.

Actins↗
PubMed1991

Extracellular poly(3-hydroxybutyrate) depolymerase from Penicillium funiculosum: general characteristics and active site studies.

An extracellular poly(3-hydroxybutyrate) (PHB) depolymerase has been isolated from Penicillium funiculosum cultural medium by a single hydrophobic column chromatography. The enzyme is a glycoprotein composed of a single polypeptide chain with a molecular mass of about 37,000 Da as analyzed by denatured sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by native gel filtration on Sephadex G-100. Its optimum activity occurs at pH 6.0. It has an isoelectric point of 5.8 and has a Km for PHB (average molecular weight = 45,000 Da) of 0.17 mg/ml. Various nonionic detergents competitively inhibit the enzyme with Ki values of 0.56 and 0.014% for Tween 80 and Triton X-100, respectively. The enzyme is extremely sensitive to diisopropyl fluorophosphate, mercuric ion, and dithiothreitol (DTT). However, sulfhydryl reagents have little or no effect on its activity. The inactivation by mercuric ion and DTT is reversible by mercaptoethanol and hydrogen peroxide, respectively. These data suggest that the enzyme may be a serine esterase and may contain an important disulfide bond. The enzyme is also inactivated by diazoacetyl and epoxide compounds at low pH, which can be prevented by PHB, indicating the presence of a critical carboxyl group at the active site. These characteristics of the enzyme are compared to other extracellular polymerases isolated from bacterial culture media.

Binding, Competitive↗
PubMed1991

High-mobility group and other nonhistone substrates for nuclear histone N-acetyltransferase.

A variety of nonhistone proteins and polyamines has been studied for their substrate activity for nuclear histone N-acetyltransferase. Nonhistone chromatin high-mobility group (HMG) proteins are found to be as good a substrate for the enzyme as histones. The enzyme also acetylates spermidine and spermine. However, protamine, bovine serum albumin, and ubiquitin are not substrates. Chymotryptic peptides of histone and HMGs retained about 64% of the substrate activity, but trypsin treatment reduced the substrate activity by more than 85%. Both N-acetyltransferase activities for HMGs and histones are copurified through salt extraction, polyethylene glycol fractionation, and chromatography on DEAE-cellulose, phosphocellulose columns, and a HPLC anionic-exchange column. The highly purified nuclear histone acetyltransferase shows similar optimal pH and ping-pong kinetics for both HMGs and histones. The Km for HMG is 0.25 mg/ml. HMGs are able to accept the acetyl group from isolated acetyl-enzyme intermediate. Denatured gel analysis shows that HMG 1 and HMG 2 are the major proteins acetylated. High salt concentrations, mononucleotides, and DNA, which inhibit histone substrate activity of the enzyme, also inhibit HMG substrate activity. These observations suggest that there is a major nuclear N-acetyltransferase which is responsible for the acetylation of both histones and HMGs and perhaps also of spermine and spermidine. Thus the regulation of the structure and function of chromatin through postsynthetic acetylation can be achieved by a single nuclear N-acetyltransferase.

Acetylation↗
PubMed1991

Traumatic asphyxia.

During a 5-year period, we treated 14 cases of traumatic asphyxia. There were 12 male and 2 female patients ranging in age from 2 to 32 years. Most suffered crushing injuries at work or were run over by motor vehicles. Mild to severe cervicofacial cyanosis and petechiae developed in all patients. A fear response was reported by 12 of the patients. Subconjunctival hemorrhage was also found in 12 patients. Nine patients had tachypnea and 7 complained of dyspnea. Most of the patients suffered some associated injuries including 8 head injuries, 7 pulmonary contusions, and 6 cases of blunt abdominal trauma. Less-associated injuries were rib fractures, brachial and radial nerve injuries, hemothorax, and pneumothorax. The hospital stay ranged from 4 to 28 days (mean, 14 days) and follow-up from 10 to 60 months (mean, 32 months). Treatment for traumatic asphyxia included measurement of arterial blood gases, oxygen supplementation, and intubation with mechanical ventilation. The patients' recovery conditions were relative to the severity of injury and the associated injuries.

Adolescent↗
PubMed1990

Regulation of Ki-ras expression in Reuber H35 cells.

Glucagon at a low concentration has a stimulatory effect on Ki-ras expression, whereas, at high concentrations the hormone suppresses the level of the Ki-ras transcripts. Incubation of the hepatoma cells with 10 microM dibutyryl cyclic AMP results in suppression of Ki-ras expression but the phorbol ester, 21-O-tetradecanoylphorbol 13-acetate (TPA) causes an increase. Down regulation of protein kinase C by prolonged exposure of hepatoma cells to TPA causes a dramatic decrease in the glucagon-stimulated effect on Ki-ras expression. The presence of diacylglycerol for 2 h in the culture medium results in a significant increase in Ki-ras expression, while treatment of the cells with 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine, a potent inhibitor of protein kinase C, leads to a dramatic reduction. The calcium ionophore, A23187 is able to stimulate Ki-ras expression, whereas, addition of verapamil or EGTA results in its suppression. The present findings suggest that the inductive effect of glucagon on Ki-ras expression at low concentrations is via the activation of protein kinase C which causes phosphorylation of some regulatory proteins that may eventually affect the level of Ki-ras mRNA. The suppressive effect of glucagon at higher concentrations is via an increase in cAMP through activation of adenylate cyclase.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1990

Inhibition of in vitro RNA synthesis by hycanthone, oxamniquine and praziquantel.

The schistosomicides, hycanthone, oxamniquine and praziquantel, were found to inhibit the in vitro RNA synthesis using isolated hamster liver nuclei. Preincubation of the nuclei with these drugs revealed that the inhibitory effect of oxamniquine was irreversible and progressed with time, whereas that of hycanthone and praziquantel was reversible. On the other hand, hycanthone and praziquantel have a high affinity for DNA but oxamniquine does not. The data indicate that the mechanism of inhibition by oxamniquine is different from that of hycanthone and praziquantel.

Animals↗