Abstract
In vivo phosphorylation of Pγ, an inhibitory subunit of cGMP-phosphodiesterase of frog (Rana catesbeiana) photoreceptor rod outer segments, was investigated using a quick-freezing technique and a newly developed method for the preparation of rod outer segments. Light-dependent phosphorylation of Pγ was observed. Okadaic acid, a potent inhibitor of protein phosphatases 1 and 2A, enhanced the apparent incorporation of 32P into Pγ suggesting that Pγ is in equilibrium between phosphorylation and dephosphorylation. Neither phorbol ester, a potent activator of protein kinase C, nor changes in the extracellular Ca2+ concentration affected the in vivo phosphorylation of Pγ