Human carnitine palmitoyltransferase 1B (CPT1B) is a highly malonyl-CoA-sensitive enzyme (IC50 = ) and has a positive determinant (residues 18–28) of malonyl-CoA inhibition. By contrast, rat carnitine palmitoyltransferase 1A is less sensitive to malonyl-CoA inhibition (IC50= ), and has both a positive (residues 1–18) and a negative (residues 18–28) determinant of its inhibition.