Growth inhibitory protein(s) in the 3T3 cell plasma membrane. Partial purification and dissociation of growth inhibitory events from inhibition of amino acid transport

It has been reported previously that a plasma membrane‐enriched fraction from 3T3 cells arrests the growth of sparse 3T3 cells early in the G₁ phase of growth (Whittenberger et al., ′78, ′79). Addition of membranes to sparse 3T3 cells also results in a decrease of the rate of transport of αaminoisobutyric acid (Lieberman et al., ′79). We have partially purified the growth‐inhibitory proteins from plasma membrane of 3T3 cells. These growth‐inhibitory proteins behave as intrinsic membrane proteins and do not require membrane lipids for activity. The partially purified proteins arrest cell growth without affecting the rate of α‐aminoisobutyric transport; thus, inhibition of both transport and cell growth are not obligatorily coupled events.