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HMG-CoA reductase (3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, official symbol HMGCR) is the rate-controlling enzyme (NADH-dependent, EC 1.1.1.88; NADPH-dependent, EC 1.1.1.34) of the mevalonate pathway, the metabolic pathway that produces cholesterol and other isoprenoids.
In archaea, HMG-CoA reductase is a cytoplasmic enzyme involved in the biosynthesis of the isoprenoids side chains of lipids. [3] Class I HMG-CoA reductases consist of an N-terminal membrane domain (lacking in archaeal enzymes), and a C-terminal catalytic region. The catalytic region can be subdivided into three domains: an N-domain (N-terminal ...
HMG-CoA synthase: Acetoacetyl-CoA condenses with another Acetyl-CoA molecule to form 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). HMG-CoA reductase: HMG-CoA is reduced to mevalonate by NADPH. This is the rate limiting step in cholesterol synthesis, which is why this enzyme is a good target for pharmaceuticals . mevalonate-5-kinase
The following reaction involves the joining of acetyl-CoA and acetoacetyl-CoA to form HMG-CoA, a process catalyzed by HMG-CoA synthase. [8] In the final step of mevalonate biosynthesis, HMG-CoA reductase, an NADPH-dependent oxidoreductase, catalyzes the conversion of HMG-CoA into mevalonate, which is the primary regulatory point in this pathway.
In biochemistry, hydroxymethylglutaryl-CoA synthase or HMG-CoA synthase EC 2.3.3.10 is an enzyme which catalyzes the reaction in which acetyl-CoA condenses with acetoacetyl-CoA to form 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). This reaction comprises the second step in the mevalonate-dependent isoprenoid biosynthesis pathway.
Because statins are similar in structure to HMG-CoA on a molecular level, they will fit into the enzyme's active site and compete with the native substrate (HMG-CoA). This competition reduces the rate by which HMG-CoA reductase is able to produce mevalonate, the next molecule in the cascade that eventually produces cholesterol.
Thus, the presence of anti-HMG CoA reductase antibodies in someone who uses a statin and has myopathy strongly supports the diagnosis. [3] CK levels increase to 10-100 times above normal (2000–20,000 IU/L) in more than 90% of cases.
Mevalonate pathway: The figure doesn't show that the HMG-CoA synthase needs another Acetyl-CoA as Substrate. Moreover, the enzyme that synthesizes mevalonic acid (HMG-CoA reductase) consumes two equivalents of NADH and releases one reduced CoA-SH.