User Contributed Dictionary
- The process of steroid production in living organisms.
Related terms
Extensive Definition
Steroid metabolism is the complete set of
chemical
reactions in organisms that produce, modify and consume
steroids. These metabolic
pathways include:
- steroid synthesis - the manufacture of steroids from more simple precursors
- steroidogenesis - the interconversion of different types of steroids
- steroid degradation.
Steroid biosynthesis
Steroid biosynthesis is an anabolic metabolic pathway that produces steroids from simple precursors. This pathway is carried out in different ways in animals than in many other organisms, making the pathway a common target for antibiotics and other anti-infective drugs. In addition, steroid metabolism in humans is the target of cholesterol-lowering drugs such as statins.It starts in the mevalonate pathway in humans,
with Acetyl-CoA as
building blocks, which form DMAPP and IPP. In following steps,
DMAPP and IPP form lanosterol, the first
steroid. Further modification belongs to the succeeding
steroidogenesis.
Mevalonate pathway
The mevalonate pathway or HMG-CoA reductase pathway starts with and ends with dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP).Regulation and feedback
Several key enzymes can be activated through DNA transcriptional regulation on activation of SREBP (Sterol Regulatory Element-Binding Protein-1 and -2). This intracellular sensor detects low cholesterol levels and stimulates endogenous production by the HMG-CoA reductase pathway, as well as increasing lipoprotein uptake by up-regulating the LDL receptor. Regulation of this pathway is also achieved by controlling the rate of translation of the mRNA, degradation of reductase and phosphorylation.Pharmacology
A number of drugs target the mevalonate pathway:- Statins (used for elevated cholesterol levels)
- Bisphosphonates (used in treatment of various bone-degenerative diseases)
Plants and bacteria
In plants and bacteria, the non-mevalonate pathway uses pyruvate and glyceraldehyde 3-phosphate as substrates., which are a large class of lipids that include the carotenoids, and form the largest class of plant natural products.Here, the isoprene units are joined together to
make squalene and then
folded up and formed into a set of rings to make lanosterol. Lanosterol can
then be converted into other steroids such as cholesterol and ergosterol. These bile acids
can then be eliminated through secretion from the liver in the bile. The expression of this
oxidase gene can be upregulated by the steroid sensor PXR when there is a
high blood concentration of steroids.