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Biomedical subjects

D A Roncari

Publications and source records attributed to D A Roncari.

At least 73 records · Page 4Linked to original sources
PubMed1977

Ribonuclease activity in renal failure: evidence for toxicity.

The normal level of serum or plasma poly C-avid ribonuclease activity is 1047 +/- 247 U/mL. Serum levels increase proportionately with elevations in serum creatinine, reaching levels of 9,500-35,000 in patients undergoing dialysis. The levels can be normalised by successful renal transplantation but not by dialysis. Purified human urinary ribonuclease, a glycoprotein enzyme similar to the serum ribonuclease, was capable of: 1) inhibiting the incorporation of 3H-thymidine into mitogen-stimulated lymphocytes; 2) inhibiting the proliferation and growth of bone marrow red cell colonies; and 3) adversely affecting the growth and viability of precursor fat cells.

Cell Division↗
PubMed1976

Mammalian fatty acid synthetase. III. Characterization of human liver synthetase products and kinetics of methylmalonyl-CoA inhibition.

When propionyl-CoA was substituted for either acetyl-CoA or butyryl-CoA in the presence of [14C]malonyl-CoA and NADPH, the pure human liver fatty acids synthetase complex synthesized only straight-chain, saturated, 15- and 17-carbon radioactive fatty acids. At optimal concentrations, propionyl-CoA was a better primer of fatty acid synthesis than acetyl-CoA. Methylmalonyl-CoA inhibited the synthetase competitively with respect to malonyl-CoA. The Ki was calculated to be 8.4 muM. These findings provide an in vitro model and offer a direct explanation at the molecular level for some of the abnormal manifestations observed in diseases characterized by increased cellular concentrations of propionyl-CoA and methylmalonyl-CoA.

Chromatography, Gas↗
PubMed1976

Cytological and enzymological characterization of adult human adipocyte precursors in culture.

Cell strains were derived from the stromal-vascular fraction of human omental adipose tissue and grown in culture. Since the purpose of this study was to isolate adipocyte precursors from adults, the cells were obtained from nonobese patients 40-60 yr of age. After treatment of adipose tissue with collagenase, mature adipocytes were separated from stromal-vascular fraction cells, and cell strains of the latter replicated in culture with a doubling time of 40-60 h. They were initially fusiform; upon reaching monolayer confluency, they accumulated lipid and became rounder. Skin fibroblasts from the same patients and grown under the same culture conditions remained fusiform and did not accumulate lipid. The stromal-vascular fraction cells of adipose tissue may be fibroblasts with the potential to become adipocyte precursors. Subcellular preparations of the cells grown from the stromal-vascular fraction revealed lipoprotein lipase activity (characterized by such properties as inhibition by 1 M NaCl) that was not detectable in skin fibroblasts. The overall specific activity of the enzymes that catalyze triglyceride synthesis was 15 times higher and that of fatty acid synthetase was 2 times higher in the cells cultured from the stromal-vascular fraction. The difference was significant in each case. Conversely, when isolated mature adipocytes were cultured, they lost considerable lipid and acquired morphological characteristics similar to those of stromal-vascular fraction cells. Thus, adipose tissue stromal-vascular fraction cells acquire in culture many of the morphological and enzymological characteristics of mature fat cells.

Adipose Tissue↗
PubMed1975

Effects of thyroid hormones on enzymes involved in fatty acid and glycerolipid synthesis.

The influence of thyroid hormones on lipid biosynthesis was studied after administration of L-thyroxine to rats for 5 days. Their weights remained the same as those of control animals, despite an approximately 3-fold increment in plasma L-thyroxine and L-triiodothyronine concentrations. The activity of acetyl-CoA carboxylase and fatty acid synthetase as well as incorporation of tritium into fatty acids were depressed significantly in epididymal adipose tissue and enhanced significantly in livers of thyroxine-treated rats. Using antibodies specific against rat liver fatty acid synthetase, it was determined that the changes in activity of this multienzymic complex were due to alterations in amount of enzyme protein. In the presence of optimal concentrations of fatty acids, radioactive sn-glycero-3-phosphate, and co-substrates, total glycerolipid synthesis (defined in this study as the sum of newly formed radioactive mono- and diacyl-sn-glycero-3-phosphate, diglyceride, and triglyceride) was decreased significantly in adipose tissue and increased in liver and heart. Thus, administration of thyroid hormone results in tissue-specific alterations in lipid biosynthesis which, at least in the case of fatty acid synthetase, are due to changes in enzyme protein content.

Acetyl-CoA Carboxylase↗
PubMed1975

Excretion of inhibitors of calcification in urine. Part I. Findings in control subjects and patients with renal stones.

The total excretion of inhibitors of in vitro calcification was measured (in inhibiting units per day) in 24-hour urine samples of 11 control subjects and 20 patients with renal calculi. A semiquantitative method incorporating the rachitic rat cartilage technique was used. In both groups there was a significant positive correlation between the number of inhibiting units per day and the daily urine volume. The mean number of inhibiting units per day was significantly (P smaller than 0.05) higher in the stone patients than in the controls. However, the stone-formers had significantly larger (P smaller than 0.01) 24-hour urine volumes. When corrections were made for urine volume there was no significant difference between the two groups. These data suggest that the underlying abnormality responsible for renal stone formation is not a persistent decrease in the total concentration of urinary inhibitors of calcification.

Adult↗
PubMed1975

Excretion of inhibitors of calcification in urine Part II. Findings in patients with chronic renal failure.

By means of a semiquantitative method incorporating the rachitic rat cartilage technique, the total urinary inhibitory activity with respect to calcification was compared in 11 control subjects and 20 patients with renal failure. The patients had significantly lower mean values of inhibiting units per day than did the control subjects. Both groups showed a significant positive correlation between the number of inhibiting units per day and urine volume. When urine volume was taken into account in the comparison, the numbers of inhibiting units for patients continued to be lower than the numbers for controls. These findings are consistent with the hypothesis that the increase of inhibitory activity observed in uremic serum is secondary to a decrease in excretion of the responsible factor (or factors) in the urine, and that the factor (or factors) in serum responsible for the inhibition are identical to those in the urine.

Adult↗
PubMed1975

Mammalian fatty acid synthetase. II. Modification of purified human liver complex activity.

Highly purified human-liver fatty acid synthetase complex was used to study the effect of several potential modifiers. Adenosine 3',5'-phosphate did not alter the activity of either purified synthetase or of multienzyme present in 700 times g supernates. Its dibutyryl derivative was also ineffective when incubated with liver slices. Fructose 1,6-diphosphate, fructose 6-phosphate, and glucose 6-phosphate stimulated significantly the activity of the purified enzyme. Fructose 1,6-diphosphate, which was most effective, decreased the Km of the synthetase for NADPH. Phosphoenolpyruvate, rac-glycero-3-phosphate and potassium phosphate were ineffective; All longg-chain fatty acyl-CoA thioesters tested were inhibitory, but this effect was not observed until the regions of their critical micellar concentrations were reached. Free myristate, palmitate, and stearate did not inhibit synthetase activity up to the highest concentration tested (1 mM)qn enzyme preparation derived from livers of fasted rats inactivated purified rat-liver 4'-phospho[14-C]pantetheine-fatty acid synthetase by releasing its prosthetic group. It also decreased the activity of the purified human-liver complex.

Bucladesine↗
PubMedDate not supplied

Purification of liver cytosolic proteins that stimulate triacylglycerol synthesis.

Heat-stable rat liver cytosolic proteins that stimulate triacylglycerol synthesis catalyzed by adipose tissue or liver microsomal enzymes have been isolated in a highly purified state. Their molecular weight ranges were found to be 35 000 - 45 000, 20 000 - 28 000, and 8000 - 12 000. The protein with molecular weight 20 000 - 28 000 and pI 7.3-7.7 was purified 4716-fold. The cytosolic proteins were stable at 85 degrees C for 15 min and were inactivated by proteases. They did not reveal any intrinsic phosphatidate phosphohydrolase or diacylglycerol acyltransferase activity, but led to enhanced conversion of phosphatidate to diacylglycerol and triacylglycerol.

Adipose Tissue↗