PROTEIN PHOSPHATASE-1 AND PHOSPHATASE-2A IN RABBIT CILIARY EPITHELIUM AND IRIS-CILIARY BODY

A significant dephosphorylation of exogenous phosphorylase a by serine/threonine protein phosphatases in tissue extracts of rabbit ciliary epithelium and iris-ciliary body was observed. Okadaic acid caused a concentration-dependent inhibition of this dephosphorylation. In a series of diluted samples, selective inhibitions of protein phosphatase 2A by 1 nM okadaic acid and protein phosphatase 1 by 1 mu M okadaic acid were determined. In the preparation of ciliary epithelium, the ratio of protein phosphatase 1 to protein phosphatase 2A activity was estimated to be 1:2. Dephosphorylation by other phosphatases was little. In the preparation of iris-ciliary body, the ratio of protein phosphatase 1 to protein phosphatase 2A activity was approximately 2.5:1. Other phosphatases were also present.