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In rat testis nuclei the activity of the selenoenzyme phospholipid hydroperoxide glutathione peroxidase (PHGPx, EC 1.11.1.12) is much higher than in other tissues and subcellular compartments, with the sole exception of mitochondria. In nuclei, the bound enzyme is solubilized by DNase I treatment, thus suggesting a binding to chromatin. Treatment with ionic strength releases about 70% of bound PHGPx, suggesting that electrostatic bonds are involved. Immunogold electron microscopy indicates the association of PHGPx with chromatin structures in isolated nuclei. A possible interpretation of these data is a PHGPx protective role against DNA peroxidative damage. Furthermore, in agreement with kinetic and structural information, PHGPx-chromatin binding could suggest an hypothetical thiol oxidase activity toward specific thiol bearing proteins which could substitute for GSH as alternative donor substrates. Such activity could give to the enzyme a new important function which is not only protective but also has a specific regulatory function in chromatin condensation.

Rat testis mitochondria contain large amounts of both seleno-enzyme phospholipid hydroperoxide glutathione peroxidase (EC 1.11.1.12, PHGPx) and alpha-tocopherol. The scavenger role of vitamin E consists of transforming the lipoperoxyl radicals into lipid hydroperoxides, thus interrupting the peroxidative cascade. These hydroperoxides are in turn substrates of the PHGPx, which is considered one of the most important specific enzymes capable of protecting, in situ, the membranes from lipid peroxidation. A connection or synergism could, therefore, be envisaged between vitamin and enzyme opposing lipid damage in the mitochondria. Here we present data concerning the HPLC evaluation of vitamin E consumption in rat testis mitochondria and mitochondrial membranes, under different conditions of PHGPx activity, after Fe2+-induced lipid peroxidation. We have found that the enzyme activity, under the conditions tested, does not spare vitamin E from its peroxidation, therefore indicating that the postulated synergism between PHGPx and alpha-tocopherol can be excluded in rat testis mitochondria.

Some aspects of the physiology of chondrocytes from horse articular cartilage were studied, since this animal model can be helpful in understanding arthritic processes. The replicative ability of articular chondrocytes, measured by the incorporation of [3H]thymidine, and their capacity of proteoglycan production, evaluated from the incorporation of [35S] sulfate, are very low. In addition, these cells do not differentiate in vitro as shown by the constant specific activity of alkaline phosphatase measured at different times in culture. Two types of potassium channels were identified by patch clamp experiments in the cell-attached configuration, one characterized by a conductance of 40 pS and the other of 100 pS. No active K+ channels were found at Vpip = 0. It was shown by Fura-2 experiments that the low replicative ability is paralleled by a modest variation of the intracellular calcium concentration after a mitogenic stimulus. 31P NMR experiments, both on slices of whole articular cartilage and on isolated cells, demonstrate that chondrocytes derive their energy mainly from the glycolytic pathway.