Structure and Functions of Phospholipid Hydroperoxide Glutathione Peroxidase

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  • リン脂質ヒドロペルオキシドグルタチオンペルオキシダーゼ (PHGPx) の構造と機能
  • リン シシツ ヒドロペルオキシドグルタチオンペルオキシダーゼ PHGPx ノ コウゾウ ト キノウ

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Abstract

Phospholipid hydroperoxide glutathione peroxidase is the only known intracellular antioxidant enzyme directly capable of reduing peroxidized phospholipids and cholesterol in membranes. PHGPx is a member of the selenoprotein family that contain the unique amino acid, selenocysteine, the active site for peroxidase activity. The gene for PHGPx has alternative transcription sites so that there are two types of PHGPx, the mitochondrial form with a leader signal sequence that targets for mitochondria and the non-mitochondrial form without this. Overexpression of PHGPx by transfection with either form of PHGPx cDNA into cells resulted in the expression of a new cellular function for PHGPx. Non-mitochondrial PHGPx inhibit the production of leukotrienes by 5-lipoxygenase by preventing the production of intracellular hydroperoxides about the nucleus, in contrast to mitochondrial PHGPx. Mitochondrial PHGPx was more effective than non-mitochondrial PHGPx in preventing cell death, necrosis and apoptosis caused by reactive oxygen species (ROS) generated in mitochondria and by exogenously added hydroperoxides. ROS have been shown to function as mediators or modulators in cellular signaling pathway such as activation of the nuclear factor KB (NFKB). PHGPx suppress the activation of NFKB through stimulation of interleukin-1. PHGPx would thus appear to serve not only as an antioxidant enzyme but to be essential for regulating signal transduction pathways triggered by ROS in cellular response.

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