Dielectric studies of ion fluctuation and chain bending in native DNA.

The high-frequency dielectric dispersion exhibited by solutions of native DNA is characterised as a function of electrolyte concentration, counterion type, temperature and pH. The data are interpreted in terms of counterion fluctuation along short segments (subunits) of the DNA chain. From calculation of the subunit length from dielectric relaxation time and increment, information is derived regarding the static and dynamic bending of the DNA chain. Activation enthalpies for the ion fluctuation process are obtained from temperature-dependent dielectric data.

Cholesterol ester hydrolysis and hormone-sensitive lipase in lactating rat mammary tissue.

Neutral cholesterol esterase activity is expressed in extracts of mammary epithelial cells. The identity of the enzyme catalyzing this hydrolysis was investigated. Anti-hormone-sensitive lipase immunoglobulin elicited the total inhibition of this activity and also immunoprecipitated a single phosphoprotein of Mr 84 kDa from mammary cell extracts previously phosphorylated in vitro with [gamma-32P]ATP and cyclic AMP-dependent protein kinase. It is concluded that mammary cell cholesterol esterase activity results from the presence of hormone-sensitive lipase.

Hormone-sensitive lipase is responsible for the neutral cholesterol ester hydrolase activity in macrophages.

Anti-hormone-sensitive lipase (HSL) immunoglobulin selectively immunoprecipitates a single 84 kDa 32P-phosphoprotein from macrophage homogenates previously phosphorylated by cyclic AMP-dependent protein kinase in the presence of [gamma-32P]ATP-Mg. This immunoglobulin also completely removes the neutral cholesterol ester hydrolase activity from macrophage homogenates. These data demonstrate that HSL is responsible for the neutral cholesterol ester hydrolase activity in macrophages and hence plays a key role in cholesterol metabolism in these cells.

Phosphorylation and activation of hormone-sensitive lipase in isolated macrophages.

Hormone-sensitive lipase (HSL) is responsible for the neutral cholesterol ester hydrolase activity in macrophages. Incubation of intact WEHI macrophages or mouse peritoneal macrophages leads to phosphorylation of HSL, which is increased by incubation with either dibutyryl cyclic AMP and 3-isobutyl-1-methylxanthine or okadaic acid. Correspondingly, these agents also activate neutral cholesterol ester hydrolase activity in intact WEHI cells. Regulation of mobilisation of esterified cholesterol in macrophages may be of antiatherogenic value, which this model system now allows us to investigate further.

The presence and role of hormone-sensitive lipase in heart muscle.

Hormone-sensitive lipase (HSL) catalyses the initial, rate-limiting, reaction in adipose-tissue lipolysis. Hormone-stimulated lipolytic activity has also been observed in the heart, where endogenous triacylglycerol is the major energy store. However, the identity of the intracellular lipase responsible has yet to be established. We have partially purified a neutral lipase from bovine heart muscle and compared its properties with those of HSL from bovine adipose tissue. The heart lipase has the same subunit Mr as HSL, is immunoprecipitated by antiserum raised against purified HSL and is phosphorylated by cyclic AMP-dependent protein kinase, apparently at the same site as HSL (as judged by h.p.l.c. of tryptic phosphopeptides). Phosphorylation of the heart lipase was found to result in increased enzyme activity, demonstrating the lipase's potential to respond to hormonal stimuli. The heart lipase was shown to be present in myocytes by its immunoprecipitation from homogenates of rat myocytes by anti-HSL antiserum. These findings are consistent with the conclusion that HSL is responsible for intracellular lipolysis in heart.