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M E Dempsey

Publications and source records attributed to M E Dempsey.

At least 37 records · Page 2Linked to original sources
PubMed1981

Synthesis of delta 5,22-cholestadien-3 beta-ol from delta 5,7,22-cholestatrien-3 beta-ol by a liver enzyme.

The rat liver enzyme system, which catalyzes reduction of delta 5,7,24-cholestatrien-3 beta-ol to cholesterol (delta 5-cholesten-3 beta-ol), converted radiolabeled delta 5,7,22-cholestatrien-3 beta-ol to delta 5,22-cholestadien-3 beta-ol, but not to cholesterol. This enzyme system thus contains membrane-bound delta 7- and delta 24-reductase and no delta 22-reductase. Kinetic and competition studies showed that the enzyme system contains a single delta 5,7-sterol delta 7-reductase, which is not influenced by unsaturation at the delta 22-position of the sterol side chain. The identity of delta 5,22-cholestadienol was established by chromatographic, spectral and chemical analyses. Use of the enzyme system and readily available delta 5,7,22-cholestatrienol provides a facile procedure for specific production of delta 5,22-cholestadien-3 beta-ol in quantity.

Animals↗
PubMed1981

Agar gel electrophoretic determination of glycosylated hemoglobin: effect of variant hemoglobins, hyperlipidemia, and temperature.

We investigated the effect of temperature, variant hemoglobins, and hyperlipidemia on determination of glycosylated hemoglobin by an electrophoretic method (Clin. Chem. 26: 1598-1602, 1980). We found that: (a) temperature variations ranging from 4 to 30 degrees C were without effect on results obtained by electrophoresis; (b) concurrent determination of glycosylated hemoglobin by electrophoresis and column-chromatography in blood specimens from 150 diabetic patients yielded almost identical mean values for both procedures when operations were carried out at 22 degrees C; (c) electrophoretic determination of glycosylated hemoglobin in whole-blood hemolysate was not affected by concentration of triglycerides; and (d) unlike column-chromatographic procedures, which underestimate the percentage of glycosylated hemoglobin in patients with hemoglobin S and C, the electrophoretic method accurately determined the proportion of glycosylated hemoglobin in these hemoglobinopathies. Evidently, electrophoresis on agar gel is an excellent alternative to cation-exchange column-chromatographic methods for glycosylated hemoglobin.

Chromatography, Ion Exchange↗
PubMed1978

An enzymatic triglyceride method that is suitable for long-term population studies.

An enzymatic triglyceride method has been shown to be a suitable alternative to the Lipid Research Clinics' extraction/fluorometry method in long-term population studies. Correlation of results obtained with this method by this laboratory (y-axis) and by the Minneapolis Lipid Research Clinic Laboratory (x-axis) during a nine-week standardization period produced a curve with an intercept of -72 mg/liter, a slope of 1.019, and a correlation coefficient of r=0.996 (n=47). During this standardization period certain methodological problems were observed and corrected. An increase in background in certain clinical specimens, caused by spontaneous degradation of NADH, was observed, accurately measured, and taken into account when appropriate.

Glycerol Kinase↗
PubMed1977

Sterol synthesis in cultured human renal cell cancer.

Studies on sterol synthesis in cultured human renal cell carcinoma were conducted in an attempt to elucidate the mechanism by which clear cell tumors accumulate cholesterol in the cytoplasm. Cultured renal cell carcinoma requires serum lipoproteins for optimal growth. In some renal cell carcinomas cellular cholesterol content was significantly higher than that present in cultured kidney cells under similar conditions. Renal cell carcinoma synthesizes sterols from labeled acetate. The rate of sterol synthesis is inversely proportional to the levels of exogenous cholesterol in the growth medium, suggesting the presence of a negative feedback mechanism. In addition, the conversion of 27-carbon-atom sterol precursors to cholesterol appears to be slow and inefficient under the presnt conditions. We conclude that an aberrant regulation of cholesterol synthesis cannot be invoked necessarily to explain cholesterol accumulation in renal cell carcinoma.

Adenocarcinoma↗
PubMed1976

Evidence for carrier proteins in bile acid synthesis. The effect of squalene and sterol carrier protein and albumin on the activity of 12alpha-hydroxylase.

The possibility that carrier proteins are involved in bile acid synthesis was investigated using rat liver homogenates. The 105 000 X g supernatant fraction was found to contain heat stable proteins that bound the bile acid precursor, 7alpha-hydroxy-4-cholesten-3-one, and increased the amount of 7alpha, 12alpha-dihydroxy-4-cholesten-3-one formed by the microsomal enzyme, 12alpha-hydroxylase. Subsequent studies were carried out to determine if squalene and sterol carrier protein or albumin, two lipid binding proteins present in the 105 00 X g supernatant fraction of rat liver homogenates, may be responsible for the effects seen with this fraction. Squalene and sterol carrier protein bound several water insoluble bile acid precursors, including 7alpha-hydroxy-4-cholesten-3-one, and increased the apparent activity of 12alpha-hydroxylase. Squalene and sterol carrier protein, however, did not bind either cholic acid or chenodeoxycholic acid. Rat serum albumin also bound 7alpha-hydroxy-4-cholesten-3-one and increased the apparent activity of 12alpha-hydroxylase. Kinetic analysis indicated that the apparent stimulation of 12alpha-hydroxylase by squalene and sterol carrier protein and albumin was due to increased solubilization of the substrate, 7alpha-hydroxy-4-cholesten-3-one. Thus, these studies indicate that bile acid precursor carrier proteins are present in the 105 000 Xg supernatant fraction of rat liver homogenates and suggest that squalene and sterol carrier protein or albumin may participate as carrier proteins in bile acid synthesis.

Animals↗
PubMed1976

Enzymatic determinations of cholesterol in high-density-lipoprotein fractions prepared by a precipitation technique.

An enzymatic method for cholesterol in serum [Clin. Chem. 20, 470 (1974)] was initially found to be unsatisfactory for measuring cholesterol in high-density-lipoprotein fractions prepared by precipitation with Mn2+. A fine precipitate formed in the cuvette and cholesterol values were falsely increased. We describe a simple, convenient method for circumventing these problems. An ethylenediaminetetraacetate solution is used to reconstitute the enzymatic reagent. Cholesterol values by this procedure correlated with those obtained by the Lipid Research Clinic's procedure for the same lipoprotein fraction preparations (regression slope, .998; Y-intercept, 8.9 mg/liter; correlation coefficient, .984; standard error of the estimate, 16.8 mg/liter). Precision of the assay, including the precipitation step, was calculated. The SDwithin day was 9.7 mg/liter and SDoverall was 23.7 mg/liter. Results for total cholesterol with the modified reagent were linearly related to concentrations exceeding 4 g/liter, thereby permitting determination of high-density-lipoproteins and total cholesterol in a single run.

Chemical Precipitation↗
PubMed1973

Squalene and sterol carrier protein: structural properties, lipid-binding, and function in cholesterol biosynthesis.

Squalene and sterol carrier protein of liver plays a general role as a vehicle for cholesterol and its water-insoluble precursors; the carrier protein is essential for enzymic cholesterol synthesis. Liver microsomal enzymes contain a small amount of endogenous carrier protein, which is readily removed by washing or purification of the enzyme. Enzymic conversion to products of a cholesterol precursor.carrier protein complex is markedly faster than that for initially unbound sterol. The protomer form of the carrier protein has a molecular weight of 16,000; during sodium dodecyl sulfate gel electrophoresis one band is observed. Phospholipid facilitates the aggregation of the protomer to the oligomer form (>150,000 daltons; purified 720-fold) accompanied by the binding of cholesterol precursors to the oligomer. The carrier protein binds fatty acids as well as cholesterol precursors, suggesting that it may more generally be a lipid carrier protein with "squalene and sterol carrier protein" describing the functional aspects of the lipid carrier in cholesterol biosynthesis. Studies with several steroids and related compounds revealed that the binding sites of lipid carrier protein must contain highly specific hydrophobic and polar regions.

Animals↗