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  • Title: Providing progesterone for pregnancy: control of cholesterol flux to the side-chain cleavage system.
    Author: Strauss JF, Christenson LK, Devoto L, Martinez F.
    Journal: J Reprod Fertil Suppl; 2000; 55():3-12. PubMed ID: 10889829.
    Abstract:
    Progesterone, which is required to support human gestation, is derived initially from the corpus luteum and subsequently from the placenta. The rate-limiting step in progesterone synthesis is the delivery of cholesterol to the mitochondrial cholesterol side-chain cleavage system. The steroidogenic acute regulatory protein (StAR) mediates this process in the corpus luteum, whereas in the placenta, which does not express StAR, a StAR homologue, MLN64, may accomplish this function. StAR expression is regulated in the ovary at the transcriptional level by a cAMP-activated signal transduction system and StAR activity is also increased acutely by protein kinase A-mediated phosphorylation. These long-term (transcriptional) and short-term (post-translational, that is, phosphorylation) mechanisms govern luteal steroidogenic activity. The StAR protein has two key functional domains. The StAR C-terminal domain increases cholesterol movement to cytochrome P450scc by promoting sterol desorption from the sterol-rich outer mitochondrial membrane, driving it to the relatively sterol-poor inner membrane. The N-terminal domain mitochondrial targeting sequence directs the StAR protein to the mitochondria.
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