Hydroxylases are a type of enzyme that catalyzes the addition of hydroxyl groups to substrates, participating in important biochemical reactions. This family includes enzymes such as cholesterol hydroxylase and proline hydroxylase, which typically contain metal ions such as iron or copper as cofactors in their structure. These enzymes are specifically localized within the cell, such as in the endoplasmic reticulum and mitochondria, and are crucial for processes like cholesterol metabolism and collagen maturation. Hydroxylases are involved in multiple signaling pathways, influencing cell proliferation and differentiation. Their gene expression is highly specific, and mutations may lead to metabolic diseases and connective tissue disorders. Enzymes of this kind are vital for maintaining the stability of the internal environment in organisms.