Deletion of D-helix in bovine pancreatic phospholipase A2.

D-Helix-deleted bovine pancreatic phospholipase A2 was designed using molecular mechanic calculations, and synthesized. Effects of the deletion on the enzymatic activity and on the structure were investigated. The enzymatic activity of the mutant protein was about 40% of that of the native one for a micellar substrate of 1,2-dioctanoyl-phosphatidylcholine. Although the Michaelis constant of the mutant enzyme was not changed, the catalytic constant was decreased. The dissociation constant of calcium ion was also changed. 1H NMR study revealed a slight conformation change around the active site of the mutant enzyme in addition to changes around the mutated region. The effect on the activity of the mutation seems to be due to the conformational changes around the active site.