âThatâs something we can test. If it does, caspase-1 inhibitors mightâand I emphasize mightâbecome a component of a curative cocktail.â G. Doitsh et al., âCell death by pyroptosis drives CD4 T-cell depletion in HIV-1 infection,â Nature, doi:10.1038/nature12940, 2013.
Decades ago it was believed that a cascade of enzymes controls the activity of HMG-CoA reductase: an HMG-CoA reductase kinase was thought to inactivate the enzyme, and the kinase in turn was held to be activated via phosphorylation by HMG-CoA reductase kinase kinase.
This is an example of negative feedback. Many enzymes are regulated by phosphorylation. A phosphate group is attached to the enzyme by another enzyme, called a protein kinase. When the enzyme is phosphorylated it changes its shape and thus its activity.