Steroid Hydoxylase Genes	

Molecular biological techniques have been employed with considerable effect to widen our knowledge of the structure of the steroid hydroxylase genes and of the mechanism of action of ACTH. Human P450 scc, P450 C17a, and P450 C21 are encoded by a single mRNA species, some 2kb in length. Bovine P450 C11b is encoded by three mRNAs, with the smallest being 4.3kb in length. Exposure of adrenocortical cells to ACTH (or cAMP) causes the accumulation of all four P450 steroidogenic enzymes, as well as of adrenodoxin and adrenodoxin reductase. Chronic exposure to ACTH involves transcription of the genes for steroid hydroxylases.