Acetyl-11-keto-beta-boswellic acid (AKAB) from Boswellia serrata and B
. carteuii acts directly on purified 5-lipoxygenase of human blood leu
kocytes at a selective site for pentacyclic triterpenes that is differ
ent from the arachidonate substrate binding site. The pentacyclic trit
erpene ring is crucial for binding to the enzyme, whereas functional g
roups (11-keto function in addition to a hydrophilic group on C4 of ri
ng A) are essential for the 5-lipoxygenase activity.