Soluble phorbol ester binding sites and phospholipid‐ and calcium‐dependent protein kinase activity in cytosol of chick oviduct

Publisher Website
Google Scholar
Abstract
A large amount of specific high affinity binding sites for tumor promoting phorbol esters as well as of a Ca2+‐ and phospholipid‐dependent protein kinase is present in cytosol of chick oviduct. 12‐O‐Tetradecanoyl‐phorbol‐13‐acetate (TPA) is able to replace either Ca2+ or the phospholipid phosphatidylserine as activators of the kinase to some extent. The maximum activity of the enzyme in the presence of Ca2+ and phosphatidylserine, however, cannot be increased further by TPA. Various second stage tumor promoters also exhibit the capacity to stimulate the protein kinase, whereas the non‐promoting phorbol ester 4‐O‐methyl‐TPA, as well as the non‐promoting, but with respect to other responses TPA‐like, calcium ionophore A23187, do not affect the kinase.