ENZYME-INHIBITION BY SODIUM-NITROPRUSSIDE

The enzyme which mediates relaxation of arterial muscle, and thus controls blood pressure, is guanylate cyclase, an enzyme with a thiol group at the active site and others elsewhere and a prosthetic haem group. Reaction of nitroprusside, a potent vasodilator, with other enzymes (papain and GAPDH) possessing a thiol group at an active site leads only slowly to enzyme inhibition by formation of disulphide bonds. Computer graphics show that the significant thiol group is accessible to the bulky nitroprusside. With enzymes containing a haem group (lactoperoxidase and catalase) inhibition by, or reaction with, nitroprusside is much faster. This suggests that the rapid vasodilator action of nitroprusside is due to its reaction with the haem group of guanylate cyclase. © 1990.