A natural heme deficiency exists in biology that allows nitric oxide to control heme protein functions by regulating cellular heme distribution

A natural heme deficiency that exists in cells outside of the circulation broadly compromises the heme contents and functions of heme proteins in cells and tissues. Recently, we found that the signaling molecule, nitric oxide (NO), can trigger or repress the deployment of intracellular heme in a concentration‐dependent hormetic manner. This uncovers a new role for NO and sets the stage for it to shape numerous biological processes by controlling heme deployment and consequent heme protein functions in biology. We hypothesize that tissues exist naturally in a heme‐deficient condition that limits the heme content and functions of heme proteins. The nitric oxide (NO) that is made in our tissues can control cell heme availability in a bimodal way, and so regulate heme protein functions in health and disease.