Prostaglandin B1: the L-shaped prostaglandin.

The crystal and molecular structure of prostaglandin B1( PGB1) has been determined. The conformation is L-shaped, with the alpha and omega side chains roughly perpendicular to one another. This arrangement differs from the "hairpin" or approximately parallel disposition of side chains observed for other prostaglandins. The omega chain, which normally turns at the 15-hydroxyl back toward the alpha chain, is fully extended. The conformation is stabilized by the conjugation of the dienone chromophore. The 15-hydroxyl, which is normally directed away from the centroid of the prostaglandin in the hairpin model, is turned inward in L-shaped PGB1. The low biological activity of PGB1 in many systems and especially its inhibition of the metabolizing enzyme 15-hydroxyprostaglandin dehydrogenase may be attributable directly to the observed L-shape conformation.