change in the expression of steroidogenic genes while the acute response involves the quick delivery of cholesterol to the site of the first enzymatic reaction. The rapid flux of cholesterol from the outer to the inner mitochondrial membrane (IMM) is mediated by the StAR protein. The IMM is the site where Cyp11a1, the enzyme catalyzing the first and rate-limiting step in the steroid biosynthetic pathway, is located. Overall there are two major classes of enzymes: the heme-containing cytochrome P450 and the hydroxysteroid dehydrogenase enzymes. The members of P450 superfamily that participate in the pathway are membrane-bound mitochondrial or endoplasmic reticulum (microsome) enzymes that utilize NADPH as an electron donor. Two proteins mediate the mitochondrial electron transfer - the flavin containing Fdxr and the iron-sulfur Fdx1; only one protein mediates the microsomal electron transfer - the P450 (cytochrome) oxidoreductase Por with two flavin cofactors. Dehydrogenases are membrane-bound mitochondrial or microsomal enzymes that utilize NAD or NADPH depending on whether the reaction is oxidation or reduction. The 27-carbon cholesterol is converted to the C₂₁ pregnenolone in a series of three chemical reactions that together constitute the step catalyzed by Cyp11a1. Isoforms Hsd3b1 and Hsd3b2 can catalyze the conversion of pregnenolone to progesterone. Desoxycorticosterone (11-deoxycorticosterone) is generated from progesterone by Cyp21a1. Two additional P450 enzymes, Cyp11b1 and Cyp11b2, are needed to generate corticosterone, and subsequently aldosterone, respectively, in the zona glomerulosa, or outer zone of the adrenal gland cortex. To see the ontology report for annotations, GViewer and download, click here.
[click to see the ontology report for related GO term - GO:0032342, associated KEGG map - map00140 and related entry at Reactome - REACT_11057.2]

The aldosterone biosynthetic pathway is part of the Steroid Hormone Biosynthesis Pathway Suite.  Click here to view the entire suite of related pathways.
...(less)