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S H Yap

Publications and source records attributed to S H Yap.

At least 163 records · Page 9Linked to original sources
PubMed1978

Effect of a short term fast on the distribution of cytoplasmic albumin messenger ribonucleic acid in rat liver. Evidence for formation of free albumin messenger ribonucleoprotein particles.

Recently, using molecular hybridization techniques with albumin [3H]cDNA, we have determined that in normally fed rats 98% of total liver polyribosomal albumin mRNA sequences are found in membrane-bound polyribosomes (Yap, S. H., Strair, R. K., and Shafritz, D. A. (1977) Proc. Natl. Acad. Sci. U. S. A. 74, 5397-5401). We now observe that a 24- to 30-h withdrawal of food leads to major changes in the amount and subcellular distribution of albumin mRNA molecules. The total amount of cytoplasmic albumin mRNA per liver and concentration of albumin mRNA per unit of membrane-bound polyribosomal RNA are decreased. However, the proportion of albumin mRNA present in the postribosomal supernatant fraction increases dramatically in a short term fast, so that it now represent 60% of total cytoplasmic albumin mRNA sequences. Most of the albumin mRNA sequences in the postribosomal supernatant fraction sediment between 30 S and 50 S. These findings suggest that albumin mRNA is probably stored in the messenger ribonucleoprotein fraction during the fasting state.

Albumins↗
PubMed1978

Identification of a high molecular weight presumptive precursor to albumin mRNA in the nucleus of rat liver and hepatoma cell line H4AZC2.

Nuclear RNAs prepared from rat liver and rat hepatoma cell line H4AZC2 have been fractionated and examined for albumin mRNA sequences by annealing to specific albumin [3H]cDNA. In both instances, sucrose gradient analysis revealed nuclear RNA molecules containing albumin RNA sequences which sedimented at 26 S (26 S albumin RNA). In contrast, cytoplasmic albumin messenger RNA sediments exclusively at 17 S. 26 S albumin RNA is resistant to both heat denaturation (65 degrees C X 5 min) and denaturation in 85% formamide (v/v), and 75% of these molecules are polyadenylated. These results provide evidence for the existence of an intact, high molecular weight, polyadenylated nuclear RNA which contains albumin mRNA sequences.

Animals↗
PubMed1977

Use of molecular hybridization to purify and analyze albumin messenger RNA from rat liver.

A new procedure is described for purification of rat liver albumin mRNA. First a population of RNA molecules is enriched for albumin mRNA by immunoprecipitation of polysomes containing albumin nascent chains. Polyadenylylated RNA is prepared from immunoprecipitates, transcribed into complementary DNA, and shown to be enriched severalfold for a particular RNA frequency component. This enriched RNA component is then purified by molecular hybridization to a limited R(0)t value (product of RNA concentration and incubation time), under conditions in which only the most abundant sequence component is annealed. Potentially, this procedure can be employed for the purification of a wide variety of mRNAs present in lesser amounts in the cell. The isolated RNA appears to be a single frequency component by hybridization to complementary DNA transcribed from itself. This RNA is a 17S species and represents 5-8% of total cytoplasmic polyadenylylated RNA. In vitro translation of the purified RNA has shown that it codes for a single polypeptide that can be identified immunologically as albumin and migrates with rat serum albumin on sodium dodecyl sulfate/polyacrylamide gels. This albumin mRNA was determined to be essentially pure by comparing its kinetics of hybridization to those obtained with rabbit alpha + beta globin mRNA and its DNA complement. The sequence complexity of purified rat albumin mRNA corresponds to 5.9 x 10(5) daltons.

Albumins↗
PubMed1977

Distribution of rat liver albumin mRNA membrane-bound and free in polyribosomes as determined by molecular hybridization.

Recently, we purified rat liver albumin mRNA and prepared albumin [(3)H]cDNA. Using albumin [(3)H]cDNA in molecular hybridization experiments, we have now determined the distribution of albumin mRNA sequences in membrane-bound and free liver polyribosomes prepared by techniques in which there is high recovery of polyribosomes without evidence of degradation. By using molecular hybridization to measure specific mRNA sequence content, numerous problems could be avoided in interpretation of results as obtained by cell-free protein synthesis or immunological methods. Under these conditions, 98% of albumin mRNA sequences in polyribosomes are found in the membrane-bound fraction.

Albumins↗
PubMed1977

Influence of chronic renal failure on protein synthesis and albumin metabolism in rat liver.

Chronic renal failure in rats leads to changes in hepatic protein synthesis and albumin metabolism at both the cellular and molecular level. In rats with chronic uremia (blood urea nitrogen greater than 45 mg/100 ml 1 mo after surgical reduction in renal mass), cell-free protein synthesis is reduced 30--40% in liver membrane-bound polyribosomes. Albumin synthesis by membrane-bound polysomes in uremia is reduced even more than the reduction in total protein synthesis. Activity of free polysomes remains norma. There is also intracellular accumulation of albumin in liver of uremic rats and a concomitant decrease in serum albumin. In normal liver, most intracellular albumin is located in the microsomal fraction, whereas in liver from uremic animals the excess albumin is found in the free cytosol fraction. These results can be explained either by a defect in synthesis of albumin by membrane-bound polysomes with release of newly synthesized albumin into the cytosol or by a reduced ability of polysomes synthesizing albumin to associate with the membrane fraction in rats with chronic renal failure.

Albumins↗
PubMed1975

Important role of tryptophan on albumin synthesis in patients suffering from anorexia nervosa and hypoalbuminemia.

The rate of albumin synthesis and the serum levels of amino acids were measured in three patients suffering from anorexia nervosa. In comparison to the control group the rate of albumin synthesis was lower for the two patients with hypoalbuminemia and the serum levels of valine, isoleucine and tryptophan also were decreased. Intravenous administration of tryptophan alone failed to increase the serum albumin level in one patient. In another patient, a 3-week period of infusion of amino acids without tryptophan failed to correct the rate of albumin synthesis or the serum albumin level. The serum albumin level rose from 37.1 g/liter to 46.8 g/liter after the infusion of amino acids plus tryptophan. The reduced supply of amino acids as the most important factor in the decrease in albumin synthesis and the important role of tryptophan in the regulation of albumin synthesis are discussed.

Adult↗
PubMed1975

Estimation of radiation dosage and transmutation effect of 14-C involved in measuring rate of albumin synthesis with 14-C-carbonate.

For direct measurement of the rate of albumin synthesis Na2 14CO3 was used intravenously. The assessment of the radiation hazard involved in the study was based on the knowledge of the minimum dose of Na214CO3 necessary for a sufficient incorporation of 14C in the guanidine-C of arginine in albumin to obtain measurable radioactivity. By measurement of expired 14CO2 and excreted 14C-urea in the urine during a 5-hr period following intravenous administration of Na214CO3 in five subjects, some quantitative data on 14C retention and radiation dosage were obtained. In comparison with animal studies, the rate of expiration of 14CO2 in man is slower. About 50% of the total radioactivity injected was lost through the respiratory route in the first hour. The total amount of expired 14C during the 5 hr of investigation was about 75% of the injected dose for the five subjects. The amount of 14C excreted as urinary 14C-urea during the 5 hr of investigation is very small in comparison with the expired 14C; it was only about 0.5% of the dose injected. The total absorbed radiation dose after complete elimination of 14C from the body was calculated with various assumptions. The extra risk of genetic damage due to disintegration of retained 14C in comparison with that of natural 14C in the body during 30 living years is about 50%.

Albumins↗
PubMedDate not supplied

Development and use of a rat albumin cDNA clone to evaluate the effect of chronic ethanol administration on hepatic protein synthesis.

A rat albumin cDNA probe (pBR alb 149) was developed in order to investigate the molecular mechanisms responsible for changes in hepatic protein synthesis after chronic administration of ethanol to rats. Rats fed a diet for up to 1 year in which 36% of calories were from ethanol, developed fatty livers but not cirrhosis. Cell-free protein synthesis with liver membrane-bound polysomes of ethanol-fed rats was increased as compared to control membrane-bound polysomes, whereas protein synthesis with free polysomes was unchanged. Total RNA extracted from liver membrane-bound polysomes and translated in a rabbit reticulocyte mRNA-dependent system showed a marked increase in albumin synthesis in the ethanol-fed group. Analysis of RNA molecules separated according to molecular weight by gel electrophoresis and hybridized with recombinant-cloned albumin cDNA demonstrated an increase in full-sized albumin mRNA species in ethanol-fed animals. Therefore, chronic ethanol administration appears to increase albumin synthesis by increasing the steady-state level of biologically active albumin mRNA in liver membrane-bound polysomes. Despite development of fatty liver, the protein synthesis machinery functions normally.

Albumins↗
PubMedDate not supplied

Regulation of low density lipoprotein receptor activity in primary cultures of human hepatocytes by serum lipoproteins.

The low density lipoprotein receptor activity was measured in primary cultures of human hepatocytes. The receptor-mediated association and degradation of low density lipoprotein increased gradually up to 140 and 190%, respectively, upon incubation of the cells with increasing amounts of whole serum (up to 100%). Preincubation of the cells with low density lipoprotein resulted in a weak downregulation of the receptor-mediated association of low density lipoprotein (only 35% reduction at 100 micrograms low density lipoprotein per ml). However, preincubation with high density lipoproteins with density between 1.16 and 1.20 gm per ml (heavy high density lipoprotein) resulted in a more than 2-fold stimulation of the receptor-mediated association of low density lipoprotein. This heavy high density lipoprotein-mediated stimulation could not be antagonized by a simultaneous addition of low density lipoprotein during that preincubation. We conclude that, in primary cultures of human hepatocytes, the downregulation of the low density lipoprotein receptor activity by low density lipoprotein is weak and completely overruled by heavy high density lipoprotein. If these results for human hepatocytes in vitro hold true for hepatocytes in vivo, our results might explain why in vivo liver cells still display low density lipoprotein receptor activity notwithstanding the exposure of these cells to physiological concentrations of low density lipoprotein.

Cells, Cultured↗
PubMedDate not supplied

Avoiding painful blood sampling in neonates by transcutaneous bilirubinometry.

BACKGROUND: Transcutaneous bilirubinometry, Bilicheck (kindly provided by Oxygen Care Company, Dublin) is a non-invasive, screening method for determining bilirubin levels in neonates. It has not previously been validated in Irish babies. AIMS: To determine the clinical accuracy and precision of Bilicheck measurements in comparison to total serum bilirubin (TSB) measurements in Irish neonates, and to determine whether Bilicheck is a useful non-invasive screening method of avoiding blood tests in neonates. METHODS: Correlation data were obtained from 53 neonates between simultaneous TSB and Bilicheck readings. Bilicheck was used to screen 100 neonates who were assessed as requiring serum bilirubin measurement. TSB was only performed on neonates whose Bilicheck was above the phototherapy line of a recognised serum bilirubin chart. RESULTS: Bilicheck and TSB were significantly correlated (r=0.890). Bland and Altman analysis showed that on average, Bilicheck read 30 micromol/l lower than TSB. Of 100 jaundiced neonates screened by Bilicheck, blood sampling was avoided in 70 because Bilicheck did not meet phototherapy guidelines. CONCLUSIONS: There is a good correlation between TSB and Bilicheck, although the latter tends to under-read by 30 micromol/l. Bilicheck may be a useful screening device to decrease the risks and discomfort associated with blood sampling in neonates.

Bilirubin↗
PubMedDate not supplied

Radiologic examination in gastric cancer. A retrospective study of 188 patients.

The accuracy in the diagnosis of gastric cancer was investigated in 188 histologically proven cases, including 12 cases of early gastric cancer. One hundred and sixty-five of 167 patients (99%) were recorded radiologically as having a gastric lesion. The initial diagnosis was carcinoma in 144 patients (86%), and benign lesion in 21 cases (13%). In 2 cases (1%) no abnormalities were seen. In 3 out of 9 patients with a partial gastrectomy (33%) an incorrect diagnosis was made. In 11 of 12 patients with early gastric cancer the radiologic examination revealed abnormal findings, but 7 of these were incorrectly interpreted as benign. A retrospective analysis of the radiologic examination in which no malignancies were reported showed that inadequacy of the examination technique and misinterpretation of radiologic signs of malignancy were the main causes of failure in diagnosing of malignancy. The rate of misinterpretation of malignancy as a benign lesion (13%) justifies the endoscopic control of every radiologically detected abnormality. The high sensitivity in detecting a lesion indicates, however, that a biphasic radiologic examination is a safe screening method in gastric cancer. Endoscopy with biopsy showed a lesion in 156 out of 160 patients (98%), but in 11 of these (7%) the initial examination did not yield histologic proof of malignancy. In 4 patients (2%) no abnormalities were observed by endoscopists. One hundred and forty-nine patients were examined with both radiology and endoscopy with biopsy. A malignant lesion with recognition of its malignant character was defined in 144 cases (97%).

Adult↗