What is the rate-limiting enzyme in cholesterol synthesis?

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Multiple Choice

What is the rate-limiting enzyme in cholesterol synthesis?

The rate-limiting step in cholesterol synthesis is the conversion of HMG-CoA to mevalonate, catalyzed by HMG-CoA reductase. This step acts as the bottleneck for the pathway, so control at this point determines how much carbon flux ultimately becomes cholesterol. Inhibiting this enzyme with statins lowers cholesterol production, illustrating its regulatory role. HMG-CoA synthase makes HMG-CoA from acetyl-CoA and acetoacetyl-CoA, but that step does not set the overall rate. Mevalonate kinase acts later in the pathway, phosphorylating mevalonate, not governing the flux. SREBP is a transcription factor that increases the expression of HMG-CoA reductase and other enzymes, modulating capacity rather than acting as the enzyme that drives the rate-limiting reaction.

The rate-limiting step in cholesterol synthesis is the conversion of HMG-CoA to mevalonate, catalyzed by HMG-CoA reductase. This step acts as the bottleneck for the pathway, so control at this point determines how much carbon flux ultimately becomes cholesterol. Inhibiting this enzyme with statins lowers cholesterol production, illustrating its regulatory role.

HMG-CoA synthase makes HMG-CoA from acetyl-CoA and acetoacetyl-CoA, but that step does not set the overall rate. Mevalonate kinase acts later in the pathway, phosphorylating mevalonate, not governing the flux. SREBP is a transcription factor that increases the expression of HMG-CoA reductase and other enzymes, modulating capacity rather than acting as the enzyme that drives the rate-limiting reaction.

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