Endurance training increased HDL cholesteryl ester metabolism in rats

We studied the effects of endurance training on the metabolism of high-density lipoprotein (HDL, 1.063 less than density less than 1.15 kg/l) cholesteryl ester and proteins in rats fed a cholesterol-rich (1%) semipurified diet. The HDL were labeled with 131I in the apoproteins and with cholesteryl-[1-14C]oleate in the esters. The HDL were intravenously administered to endurance-trained (n = 10) and cage-sedentary (n = 10) rats. Blood samples were taken over the next 36 h while the rats were conscious and feeding. The trained rats had higher plasma HDL cholesterol (0.72 vs. 0.28 mM) and HDL apoprotein (461 vs. 267 mg/l) concentrations than the sedentary rats. The production or disposal rate of HDL cholesteryl ester was higher in the trained rats (1.36 mumol/h) than in the sedentary rats (0.72 mumol/h), whereas the production or disposal rate of HDL apoproteins was similar in the trained (0.64 mg/h) and sedentary (0.60 mg/h) rats. The residence time of the HDL cholesteryl esters (4.72 +/- 0.22 vs. 3.37 +/- 0.21 h) and HDL apoprotein (7.65 +/- 0.36 vs. 4.55 +/- 0.28 h) was longer for the trained than for the sedentary rats. These data indicate that endurance training resulted in a significant change in the metabolism of HDL cholesteryl esters and apoproteins as well as an increase in their concentrations.     

Nucleotide sequences of the genes encoding fructosebisphosphatase and phosphoribulokinase from Xanthobacter flavus H4-14

The genes encoding fructosebisphosphatase and phosphoribulokinase present on a 2.5 kb SalI fragment from Xanthobacter flavus H4-14 were sequenced. Two large open reading frames (ORFs) were identified, preceded by plausible ribosome-binding sites. The ORFs were transcribed in the same direction and were separated by 39 base pairs. They encoded proteins of 364 and 291 amino acids, with molecular masses of 38739 and 33409 Da, respectively. The ORFs were identified as the genes encoding FBPase and PRK, respectively, on the basis of similarity with FBPase and PRK sequences from other sources.     

Density profile and cholesterol concentration of serum lipoproteins in experimental animals and human subjects on hypercholesterolaemic diets

The density profile of Sudan black stained serum lipoproteins was studied in human subjects and various animal species on diets supplemented with cholesterol. In the animals studied (rabbits, calves, mice, chickens, rats and guinea-pigs), the feeding of cholesterol resulted in an elevation of serum cholesterol levels together with marked changes in the density profile and the cholesterol concentration of the serum lipoproteins. Large differences between animal species in their response to dietary cholesterol were found. In a human subject, an increased concentration of serum cholesterol due to the consumption of a diet supplemented with six egg yolks per day was reflected in an elevated level of LDL cholesterol, while changes in the density profile of stained serum lipoproteins were not observed. In subjects with familial type III and type IV hyperlipoproteinaemia, marked differences in the density profile of lipoproteins were found when compared with that of normolipoproteinaemic subjects. The density profile of stained lipoproteins in the type III patients was remarkably similar to that in cholesterol-fed chickens and lean Zucker rats.     

In vitro incorporation of radiolabeled cholesteryl esters into high and low density lipoproteins

We have developed and validated a method for in vitro incorporation of radiolabeled cholesteryl esters into low density (LDL) and high density lipoproteins (HDL). Radiolabeled cholesteryl esters dissolved in absolute ethanol were mixed with LDL or HDL in the presence of lipoprotein-deficient serum (LPDS) as a source of core lipid transfer activity. The efficiency of incorporation was dependent on: a) the core lipid transfer activity and quantity of LPDS, b) the mass of added radiolabeled cholesteryl esters, c) the length of incubation, and d) the amount of acceptor lipoprotein cholesterol. The tracer incorporation was documented by repeat density gradient ultracentrifugation, agarose gel electrophoresis, and precipitation with heparin-MnCl2. The radiolabeling conditions did not affect the following properties of the lipoproteins: 1) chemical composition, 2) electrophoretic mobility on agarose gels, 3) hydrated density, 4) distribution of apoproteins on SDS gels, 5) plasma clearance rates, and 6) immunoprecipitability of HDL apoproteins A-I and A-II. Rat HDL containing radiolabeled cholesteryl esters incorporated in vitro had plasma disappearance rates identical to HDL radiolabeled in vivo.     

Studies on chlorophyllase. The mechanism of the action of lecithin liposomes on enzyme activity and the function of the carbohydrate moiety of the enzyme

A sensitive and continuous fluorescence assay of chlorophyllide formation in the presence of lecithin liposomes has been developed. The mechanism of the enhancing effect of lecithin on chlorophyllase-catalyzed hydrolysis of chlorophyll has been elucidated. Using both fluorescence and biochemical assays, the function of the concanavalin A-reactive carbohydrate moiety of chlorophyllase has been investigated. Experiments on the interaction of chlorophyllase with concanavalin A show that the sugar group not only stabilizes the enzyme, but also is essential for the manifestation of enzyme activity. From a comparison of the results obtained with solubilized and membrane-bound enzyme, it is concluded that the active site is situated on the outside of the thylakoid membrane. Mg²⁺, in combination with dithiothreitol, activates chlorophyllase. In the presence of Mg²⁺, an abnormal pH dependence of the inhibiting effect of concanavalin A on chlorophyllase-catalyzed chlorophyll hydrolysis and the reversibility of this effect through the addition of α-methyl-D-mannoside have been observed. The cause of this atypical reaction as well as of other Mg²⁺ effects is discussed.     

Homology of Drosophila yolk proteins and the triacylglycerol lipase family

Drosophila yolk proteins consist of a set of related proteins of 50,000 Mr. They are derived from slightly larger precursors by cleavage of a signal peptide. In this respect, they differ from the yolk proteins of other insects which are proteolytic fragments of precursors of 200,000 Mr or larger, termed vitellogenins and probably homologous to the vitellogenins of other egg-laying species. We report here a comparative amino acid analysis demonstrating that the Drosophila yolk proteins are non-homologous to the vitellogenin group of yolk proteins, but surprisingly are related to the triacylglycerol lipase family.     

The preparation of human hemoglobin alpha-subunit and a study of its monomer-dimer association.

An improved procedure for the isolation of the alpha-subunit of human hemoglobin is described. The monomer-dimer equilibrium in alpha-subunit solutions has been studied by boundary analysis in gel filtration, sedimentation velocity, sedimentation equilibrium, and cross-linking with dimethyl adipimidate. A dissociation constant has been determined from the sedimentation equilibrium data. The reaction with haptoglobin of cross-linked alpha-subunit showed that the dimer fraction wound form a stable complex.     

The restriction endonuclease cleavage map of rat liver mitochondrial DNA.

Mitochondrial DNA from rat liver contains six sites for cleavage by the restriction endonucleases Hind III and EcoRI. A large stretch of DNA, comprising about 40% of the mitochondrial genome is not cleaved by either of the enzymes; eight cleavage sites are located on a DNA stretch of 35% of the genome length suggestive of an unequal distribution of the A - T baspairs over the molecule. The number of Hind III and Eco R I fragments is much higher than reported for other mammalian mitochondrial DNAs up to now.