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R B Clayton

Publications and source records attributed to R B Clayton.

30 records · Page 2Linked to original sources
PubMed1968

Behavior of sterols of insect muscle during homogenization and differential centrifugation.

Labeled sterol introduced in vitro into a homogenate of insect muscle became distributed in the various subcellular fractions in a manner similar to that obtained by fractionation of muscle of insects to which labeled sterol had been administered in vivo. If two differently labeled sterols, cholesterol and cholestanol, were added to the in vitro preparation, the ratio of concentrations of the two compounds remained the same for the supernatant as for the particulate fractions. This was true for widely different total concentrations of the sterols. This result differs from that previously reported for the in vivo incorporation of these sterols and is viewed as further support for the proposal that some form of structural selectivity regulates the in vivo incorporation of the sterols into the membranous parts of the cell. Mitochondria into which labeled sterols had been incorporated under various conditions, both in vitro and in vivo, were combined with a second, unlabeled homogenate which was then fractionated in the usual way and assayed for radioactivity to assess the extent of redistribution of labeled sterol to other fractions. The results indicate that in the usual homogenization and fractionation procedure there is little redistribution of mitochondrial sterol that has been incorporated under long-term in vivo conditions. Sterol taken up by the mitochondria in vitro was redistributed to a significantly greater extent and somewhat similar results were obtained with sterol incorporated under short-term in vivo conditions. No differences between cholesterol and cholestanol with respect to their tendency to redistribute to other subcellular fractions could be detected in any of these experiments.

Carbon Isotopes↗
PubMed1966

Distribution and dynamic state of sterols and steroids in the tissues of an insect, the roach Eurycotis floridana.

The total concentrations of sterols in the tissues of the roach, Eurycotis floridana, reared under aseptic conditions and on semisynthetic diets, are similar to, but somewhat lower than, those of tissues of vertebrates. Total concentrations of tissue sterols are relatively independent of dietary concentration of sterols whether the diet contains 0.1% cholesterol as the sole sterol, or a "minimal cholesterol" mixture (0.1% cholestanol together with 0.005% cholesterol). Under the latter conditions the cholesterol is incorporated preferentially into most tissues and remains almost exclusively unesterified, while the cholesterol-sparing sterol is esterified to varying degree, depending upon the tissue. The turnover of tissue sterols has been studied. Cholesterol of the tissues of adult insects grown on a diet containing this sterol alone may be displaced by cholestanol fed as 5% of the total diet, initially at an appreciable rate but later much less rapidly. In growing insects that have received a diet containing cholestanol together with minimal cholesterol, the unesterified cholesterol turns over slowly in all tissues and immeasurably slowly in some. The unesterified sparing sterol, on the other hand, turns over at a much greater rate. The turnover of sterols during growth is accompanied by a shift of sterols from the unesterified to the esterified pool in all tissues. The fat body of the growing insect stores sterols (apparently as their esters) that have been displaced from other tissues. The fat body of the adult does not show evidence of sterol storage. Polar derivatives of sterols are present in minor amount in all tissues of the insect, most abundantly in the mid-intestine and gastric caeca. These compounds seem likely to be C(27) steroids.

Animals↗
PubMed1966

The intracellular distribution of sterols in Eurycotis floridana and its possible relation to subcellular membrane structures.

The roach Eurycotis floridana was reared on a semisynthetic diet containing minimal cholesterol-4-(14)C (0.005%) supplemented with cholestanol-7alpha-(3)H (0.1%), and various tissues of the insect were separated into "nuclear," "mitochondrial," and "microsomal" fractions by differential centrifugation. Muscle and salivary gland were satisfactorily fractionated and results from these are reported together with some, as yet, incomplete results for nerve. The major concentrations of unesterified sterol and lipid phosphorus were in the mitochondrial and microsomal fractions. The unesterified sterols of the subcellular fractions were separated by alumina and gas-liquid chromatography. The emergent peaks corresponding to cholesterol, cholestanol, and Delta(7)-cholestenol (a metabolite of cholestanol) were assayed for (3)H and (14)C. No sterol was confined to any one subcellular fraction. The proportions of the three sterols were closely similar in all membranous components of the same tissue, but were different in different tissues. It is suggested that the different subcellular membranes of a given tissue contain similar repeating structural units in which the individual sterols occupy sterically characteristic spaces.

Animals↗