Effects of free oxygen radicals on Ca2+ release mechanisms in the sarcoplasmic reticulum of scallop (Pecten jacobaeus) adductor muscle.

In vitro oxyradical effects on SR Ca2+ regulation were studied by using a SR-containing cell-free preparation from scallop (Pecten jacobaeus) adductor muscle. Ca2+ variations were fluorimetrically detected after incubation with Fluo-3 in the presence of ATP. Exposure to Fe3+/ascorbate produced dose-dependent Ca2+ release from SR vesicles, eventually leading to massive Ca2+ loss.

Effects of heavy metals on the Ca(2+)-ATPase activity present in gill cell plasma-membrane of mussels (Mytilus galloprovincialis Lam.).

1. Heavy metals (Hg2+, Cu2+, Cd2+, Zn2+, Pb2+) at micromolar concentrations strongly inhibit the Ca(2+)-ATPase activity present in the plasma-membrane obtained from the gill cells of Mytilus galloprovincialis Lam. Heavy metals act through inhibition of the formation of the phosphorylated intermediate.

Seasonal variations in the antioxidant defence systems and lipid peroxidation of the digestive gland of mussels.

1. The seasonal variations in the level of antioxidant compounds (glutathione (GSH), vitamin E, carotenoids) and in the activity of antioxidant enzymes, superoxide dismutase (EC 1.15.

Isolation and biochemical characterization of the microsomal fraction from the digestive gland of mussel Mytilus galloprovincialis Lam.

A procedure to prepare microsomes from the mussel digestive gland is proposed. The data concerning the biochemical characterization of this subcellular fraction shows a typical RNA:protein ratio, but the presence of hydrolytic enzymes was also found; therefore a mixture of hydrolase inhibitors to study the different biochemical characteristics was used. The biochemical data demonstrate that glucose-6-phosphatase activity (G6Pase), a typical microsomal marker in mammalian cells, is not present in mussel digestive gland microsomes but a high non-specific phosphatase activity was detected.

Increased levels of rat liver RNA polymerase I(A) and I(B) following the administration of triiodothyronine.

The levels of the transcribing RNA polymerase I(B) in the nucleus and of the non-transcribing RNA polymerase I(A) in the cytoplasm are both approximately doubled 24 h after a single i.p. injection of triiodothyronine into thyroidectomized rats.

[Influence of temperature on the preferential extraction of RNA polymerase I from hepatic nuclei of the rat].

RNA polymerase I has been extracted from rat liver nuclei by three consecutive washings at 0 degrees C with a medium of relatively low ionic strength (0.15 M KCl) containing Mg++ rather than by incubating the organelles at 37 degrees C in the same medium, as originally proposed by Chesterton and Butterworth. The modified technique, which has the advantage of preventing a temperature-mediated conversion of form IB to IA, gives similar yields of RNA polymerase I and retains the capacity of preferentially extracting the enzyme with respect to the other forms of nuclear RNA polymerase.

Functional state of rat liver RNA polymerase IA and IB.

Phosphocellulose chromatography has been employed to characterize RNA polymerase I present in two different functional states in rat liver cells. The actively transcribing enzyme solubilized from nuclei appears to belong both to the IA and IB classes, whereas the non-transcribing enzyme present in the cytoplasmic fraction has been found to belong only to the IA class. Indirect and direct evidence indicates, however, that in isolated nuclei only the IB form is to be regarded as the physiological form of the enzyme, the IA form arising as a procedural artefact during the extraction process.

Increased activity of rat liver nucleolar protein kinase following triiodothyronine administration.

Triiodothyronine (T3) administration to thyroidectomized rats induces a significant increase in the nucleolus-associated protein kinase (ATP:protein phosphotransferase, EC 2.7.1.

Increased in vitro phosphorylation of rat liver nucleolar proteins following triiodothyronine administration.

It has been shown that triiodothyronine (Ta) administration to thyroidectomized rats induces an increase in the in vitro net 32P uptake into liver nucleolar proteins. Such an increase depends on a stimulation of the nucleolus-associated protein kinase activity and not on a lower dephosphorylation rate.