Search PubMed⌕ Search

Biomedical subjects

C C Liew

Publications and source records attributed to C C Liew.

At least 145 records · Page 8Linked to original sources
PubMed1978

Nuclear proteins in the heart of the cardiomyopathic Syrian hamster. Phosphorylation of phenol-soluble nonhistone proteins.

We examined incorporation of 32P into phenol-soluble nonhistone nuclear acidic proteins (NHNP) obtained from myolytic, hypertrophic, and failing phases of hamster cardiomyopathy. NHNP from these dystrophic hamster hearts were phosphorylated much less than their controls, despite a 9-fold increase in uptake of 32P into their nuclei. After fractionation of NHNP by isoelectrofocusing polyacrylamide gel electrophoresis, two major fractions focusing from pH 6.0 to 6.2 and 6.6 to 6.8 were highly phosphorylated in both the control and dystrophic hearts. The latter fraction was much more phosphorylated in the control. Two fractions of NHNP focusing at pH 4.9 and 5.1 were more highly phosphorylated in the dystrophic hearts than in the controls. Autoradiographs obtained from the two-dimensional polyacrylamide slab gel electrophoresis showed that two proteins (pH 4.9 and 5.1; mol wt 25,000 and 60,000, respectively) were highly phosphorylated in the dystrophic heart. There was no detectable phosphorylation of these proteins in the controls. These changes in the phosphorylation of cardiac NHNP may be important in determining the alteration of gene expression in hamster cardiomyopathy.

Animals↗
PubMed1977

Identification of specific phosphoproteins in nuclease-digested chromatin subunits.

Rat liver chromatin subunits (nucleosomes), which were isolated from nuclease-digested chromatin either treated or not treated with 0.5% sodium deoxycholate and 5% Triton X-100, were found to be similar with regard to sedimentation at 11 S and appeared as spherical particles with a diameter of about 100 A (1 A = 0.1 nm) in electron micrographs. The ratio of histone to nonhistone chromatin proteins (NHCP) in these subunits was 1:0.1 in the absence of detergents and 1:0.25 in the presence of detergents. After ultracentrifugation of the nuclease-digested chromatin in a 5--30% sucrose density gradient two groups of phenol-soluble NHCP were identified, one being released in the top of the gradient (fA) and the other still bound to the chromatin subunits after the nuclease digestion (fB). Two specific phosphoproteins were found in fA, one (A4) with molecular weight (MW) 39 000, pI 5.3--6.0, and the other (A5) with MW 31 000, pI 5.1--5.8. These proteins were not present in fB. Another protein in fB (B2) was highly phosphorylated, with MW 68 000, PI 6.5--8.2, and this was not found in fA. These phosphoproteins were further characterized and found to contain phosphoserine. The presence of specific phosphorylated protein(s) in fB suggests that the interaction of phosphoproteins with DNA in the eukaryotic genome is more than a random process.

Animals↗
PubMed1976

Identification of nonhistone chromatin proteins in chromatin subunits.

Rat liver chromatin was digested by micrococcal nuclease. More than 80% of the enzyme-digested chromatin could be recovered after centrifugation. Treatment with sodium deoxycholate and Triton X-100 at concentrations of 0.5% in the final chromatin suspension gave a higher recovery. Chromatin subunits were fractionated on a 5-30% linear sucrose density gradient. Approximately 35% of the chromatin subunits could be recovered from the gradient. Chromatin subunits and their DNA fragments were identified by gel electrophoresis and ultracentrifugation. The presence of nonhistone chromatin proteins (NHCP) in chromatin subunits was demonstrated by the following criteria: (i) Quantitative analysis showed that the mass ratio of histone to NHCP, in the presence or absence of detergents, was 1:0,25 or 1:0.1, respectively. (ii) After the removal of acid-soluble protein from the subunits, it was found that most of the phenol-soluble NHCP were similar to total chromatin NHCP. However, four major fractions of these phenol-soluble NHCP were found to be enriched in the subunits as identified by two-dimensional polyacrylamide gel electrophoresis. (iii) Experiments using an exchange of isotope-labeled and nonlabeled chromatin showed that NHCP were tightly bound to the chromatin subunits.

Animals↗
PubMed1976

Fractionation of nucleolar proteins by two-dimensional gel electrphoresis.

Isolation of nucleolar proteins was obtained by dissociation in the presence of urea-guanidine hydrochloride, followed by high-speed centrifugation to remove nucleic acids. At least 31 fractions of nucleolar proteins were detected by isoelectrofocusing gel electrophoresis in pH range 3.5-10. Following two-dimensional gel electrophoresis on sodium dodecyl sulfate-polyacrylamide slab gels, more than 100 components of nucleolar proteins were identifieid. Two-thirds of nucleolar proteins were located in the pH range 5-8 following isoelectrofocusing. The molecular weights of these classes of proteins were shown to be mostly 30000-70000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Animals↗
PubMed1975

Lysergic acid diethylamide: effect on histone acetylation in rabbit brain.

Lysergic acid diethylamide increased acetylation of histones in rabbit cerebral hemispheres and midbrain 30 minutes after intravenous administration of the drug at doses of 10 and 100 micrograms per kilogram of body weight. Evidence for the stimulation of acetylation in individual histone bands was obtained after separation by electrophoresis on polyacrylamied gels.

Acetylation↗
PubMed1975

Rat liver nuclerar protein kinases.

We have shown that nuclei isolated by two methods contain grossly different amounts of cyclic AMP-dependent histone kinase activity. Repeated washing of the isolated nuclei with a low ionic strength buffer removed the majority of the cyclic AMP-dependent histone kinase and cyclic AMP binding activity. Nuclear cyclic AMP-dependent histone kinase activity accounted for only 0.42% of the total cytoplasmic enzyme activity. Similarly, the lactate dehydrogenase activity associated with liver nuclei represented only 0.07% of the total cytoplasmic activity. The isolated liver nuclei contained only 0.27% of the total homogenate glutamate dehydrogenase activity and 1.7%of the total homogenate glucose-6-phosphatase activity. The cyclic AMP-dependent histone kinase behaves as a cytoplasmic rather than a nuclear enzyme. We have also shown that using crude extracts, one can achieve separation of the two nuclear casein kinases, NI and NII, on sucrose density gradients in the presence of 0.5M NaCl. Nuclear casein kinases NI and NII had sedimentation coefficients of 3.0 and 593 S, respectively, in the presence of 0.5 M NaCl. Under conditions of low ionic strength, all of the casein kinase activity in the crude nuclear extract sedimented as one peak with a seminentation coefficient of 7.3 S. The aggregation-disaggregation which occurred in the crude extract was reversible and was mainly due to the aggregative and disaggregative properties of casein kinase NII. The two nuclear casein kinases have different affinities for chromatin. When nuclei were disrupted in a hypotonic solution and extracted with a buffercontaining 0.14 M NaCl, casein kinase NII could be completely extracted from the viscous nuclear material. Although a significant amount of casein kinase NI was extracted by the buffer containing 0.14 M NaCl, re-extraction of the nuclear material with a buffer containing 0.5 M NaCl yielded substantial amounts of casein kinase NI, and a final extraction with a buffer containing 1.0 M NaCl yielded measurable amounts of casein kinase NI. No casein kinase NII activity could be detected in the 0.5 M and 1.0M NaCl extracts.

Animals↗
PubMed1975

Covalent modification of nuclear proteins during aging.

An in vitro assay system has been established to study acetylation and phosphorylation of nuclear proteins from isolated nuclei. Phosphorylation of neclear proteins reached a peak within 5 min while maximum acetylation occurred about 10 min later. The rate of acetylation of liver nuclear proteins in 15 min incubation was significantly higher in "old" mice (29 mo) than in "young" mice (2 mo), while there was no difference in phosphorylation. When nuclear histones were fractionated by polyacrylamide-urea electrophoresis the acetylation of histone F3 was increased in "old" mice to 129% and F2al to 112% of the values in "young" mice. Acetylation of phenol-soluble nuclear acidic proteins was increased to 250% and phosphorylation to 138% in "old" mice as compared to "young" mice. This increase in covalent modification of acidic proteins was found in tow specific fractions when separated by SDS-polyacrylamide gel electrophoresis. By contrast, the labeling of nucleoplasmic proteins, soluble in 0.14 M NaCl, showed no significant difference between the two ages.

Acetylation↗
PubMed1974

Isolation of nuclear acidic proteins from rat tissues. Characterization of acetylated liver nuclear acidic proteins.

Nuclear acidic proteins isolated from rat brain, heart, kidney and liver showed similar, complex patterns on electrophoresis in sodium dodecyl sulphate-polyacrylamide gels. The contamination of nuclear acidic proteins by nuclear-membrane acidic proteins was found to the extent of 11%. Incorporation of [(3)H]acetate into the various nuclear acidic proteins in vivo, which were fractionated by polyacrylamide-gel electrophoresis, differed from tissue to tissue. Hydrolysis of these acetylated nuclear acidic proteins with 6m-HCl at 110 degrees C released 70% of the radioactivity, which indicated that labile acetyl groups had been incorporated into these proteins. Analysis of [(3)H]acetate-labelled nuclear acidic proteins revealed two acetylated amino acid residues, N(2)-acetylserine and N(2)-acetyl-lysine. The significance of the role played by nuclear acidic proteins in relation to gene regulation is discussed.

Acetates↗
PubMed1974

Acetylation of reticulocyte ribosomal proteins at time of protein biosynthesis.

When rabbit reticulocytes were incubated in vitro with [(3)H]acetate, their ribosomal proteins were rapidly acetylated within 10 min. Polyacrylamide-urea gel electrophoresis showed that several major ribosomal protein fractions were highly acetylated. By the double-isotope labeling technique, the incorporation of [(3)H]acetate and [(14)C]aminoacid mixture into ribosomal proteins and nascent chains was found to be closely associated. Sodium fluoride abolished the acetylation of ribosomal proteins, whereas cycloheximide reduced the acetylation of ribosomal proteins to a much lower level. These findings suggest that acetylation of ribosomal proteins may be involved in the formation of the initiation complex during protein biosynthesis.

Acetates↗