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Aldosterone synthase, also called steroid 18-hydroxylase, corticosterone 18-monooxygenase or P450C18, is a steroid hydroxylase cytochrome P450 enzyme involved in the biosynthesis of the mineralocorticoid aldosterone and other steroids. The enzyme catalyzes sequential hydroxylations of the steroid angular methyl group at C18 after initial 11β ...
Aldosterone release causes sodium and water retention, which causes increased blood volume, and a subsequent increase in blood pressure, which is sensed by the baroreceptors. [39] To maintain normal homeostasis these receptors also detect low blood pressure or low blood volume, causing aldosterone to be released.
Pregnenolone (P5), or pregn-5-en-3β-ol-20-one, is an endogenous steroid and precursor/metabolic intermediate in the biosynthesis of most of the steroid hormones, including the progestogens, androgens, estrogens, glucocorticoids, and mineralocorticoids. [1]
These enzymes are nearly identical (they share 11β-hydroxylation and 18-hydroxylation functions), but aldosterone synthase is also able to perform an 18-oxidation. Moreover, aldosterone synthase is found within the zona glomerulosa at the outer edge of the adrenal cortex ; 11β-hydroxylase is found in the zona fasciculata and zona glomerulosa .
The first enzymatic step in the production of all steroid hormones is cleavage of the cholesterol side chain, a reaction that forms pregnenolone as a product and is catalyzed by the enzyme P450scc, also known as cholesterol desmolase. After the production of pregnenolone, specific enzymes of each cortical layer further modify it.
Cholesterol side-chain cleavage enzyme (20,22-desmolase) – steroid synthesis; 17,20-Lyase (17,20-desmolase) – androgen synthesis; Steroid hydroxylases. 11β-Hydroxylase – corticosteroid synthesis; 17α-Hydroxylase – androgen and glucocorticoid synthesis; 18-Hydroxylase (aldosterone synthase) – mineralocorticoid synthesis
Corticosterone has only weak glucocorticoid and mineralocorticoid potencies in humans and is important mainly as an intermediate in the steroidogenic pathway from pregnenolone to aldosterone. Corticosterone is converted to aldosterone by aldosterone synthase , found only in the mitochondria of glomerulosa cells.
The effects of insulin vary depending on the tissue involved, e.g., insulin is most important in the uptake of glucose by muscle and adipose tissue. [2] This insulin signal transduction pathway is composed of trigger mechanisms (e.g., autophosphorylation mechanisms) that serve as signals throughout the cell. There is also a counter mechanism in ...