Belonging to the sterol desaturase family, ERG25 is a 293 amino acid enzyme that performs the first of three enzymatic steps required to remove the two methyl groups leading to cholesterol. ERG25 is a multi-pass membrane protein that resides within the plasma membrane and the membrane of the endoplasmic reticulum. Concentrations of ERG25 mRNA increase when subjected to low iron growth conditions, suggesting that the enzyme is not regulated by iron but by an end product of the ergosterol pathway. Low-density lipoprotein (LDL) downregulates ERG25 expression in the vascular wall, an event that may be inhibited via SREBP overexpression. ERG25 is encoded by a gene located on human chromosome 4q32.3.