PON1

Serum paraoxonase/arylesterase 1 (PON1) also known as A esterase , homocysteine thiolactonase or serum aryldialkylphosphatase 1 is an enzyme that in humans is encoded by the PON1 gene. Paraoxonase 1 has esterase and more specifically paraoxonase activity. Serum PON1 is found in all mammalian species studied so far but is not present in the serum of birds, fish and reptiles or in insects. PON1 is the first discovered member of a multigene family also containing PON2 and PON3, the genes for which are located adjacent to each other on chromosome 7.

Structure

Human PON1 is a glycoprotein composed of 354 amino acids and has a molecular weight of 43000 Daltons which associates with high-density lipoprotein (HDL, "good cholesterol") in the circulation. Serum PON1 is secreted mainly by the liver although local synthesis occurs in several tissues and PON1 protein is found in almost all tissues. X-ray crystallography has revealed the structure of PON1 to be a 6 bladed propeller with a unique lid structure covering the active site passage and which allows association with HDL. The structure contains 2 calcium ions which are essential for catalytic activity and enzyme stability.