Effects of chronic taurine treatment on the electrical and contractile properties of skeletal muscle fibers of aged rats

Heterologous expression, purification, and characterization of recombinant rat cysteine dioxygenase

Cysteine dioxygenase (CDO, EC 1.13.11.20) catalyzes the oxidation of cysteine to cysteine sulfinic acid, which is the first major step in cysteine catabolism in mammalian tissues. Rat liver CDO was cloned and expressed in Escherichia coli as a 26.8-kDa N-terminal fusion protein bearing a polyhistidine tag. Purification by immobilized metal affinity chromatography yielded homogeneous protein, which was catalytically active even in the absence of the secondary protein-A, which has been reported to be essential for activity in partially purified native preparations. As compared with those existing purification protocols for native CDO, the milder conditions used in the isolation of the recombinant CDO allowed a more controlled study of the properties and activity of CDO, clarifying conflicting findings in the literature. Apo-protein was inactive in catalysis and was only activated by iron. Metal analysis of purified recombinant protein indicated that only 10% of the protein contained iron and that the iron was loosely bound to the protein. Kinetic studies showed that the recombinant enzyme displayed a K(m) value of 2.5 +/- 0.4 mm at pH 7.5 and 37 degrees C. The enzyme was shown to be specific for l-cysteine oxidation, whereas homocysteine inhibited CDO activity.

Immunocytochemical localization of taurine in different muscle cell types of the dog and rat

The presence and distribution of the amino acid taurine in different muscle cell types of the dog and rat was examined by immunocytochemical methods. The light microscope study revealed that smooth muscle cells were similarly immunoreactive for taurine, whereas skeletal muscle fibres showed wide differences in taurine immunoreactivity among individual cells. Some skeletal fibres were strongly immunoreactive whereas others did not display immunolabelling. Mononucleated satellite cells, found adjacent to skeletal fibres in a quiescent stage, were also immunostained. Other myoid cells, such as testicular peritubular cells showed a cytoplasmic and a nuclear pool of taurine. By means of electron microscope immunolabelling, the subcellular localization of taurine was studied in vascular and visceral smooth muscle cells. Taurine was present in most subcellular compartments and frequently appeared randomly distributed. Taurine was localized on myofilaments, dense bodies, mitochondria, the plasma membrane and the cell nucleus. Moreover, the labelling density within individual smooth muscle cells was variable and depended on the state of contraction of each single fibre. Contracted cells showed a higher density of gold particles than relaxed cells. Unmyelinated nerve fibres, found adjacent to smooth muscle cells from the muscularis mucosae and the lamina propria of the stomach, were unstained or poorly stained.