Identification of a calcium- and phospholipid- dependent phorbol ester binding activity in the soluble fraction of mouse tissues.

A soluble cytosolic protein which specifically and with high affinity binds tumor promoting phorbol ester tumor promoters was found in mouse tissues Calcium and phosphatidyl serine had to be included in the binding assay to obtain maximal binding activity by the soluble receptor. Soluble binding activity levels paralleled the levels of membrane associated binding activity with the soluble activity accounting for 27% to 80% of the total. Except the calcium and phospholipid requirement, no difference was found between the soluble and membrane associated receptors, suggesting that they are the same protein which can move between the soluble cytosol and cell membranes.