Effect of okadaic acid on membrane protein phosphorylation in human erythrocytes.

Okadaic acid, penetrating the human erythrocytes, almost completely inhibits P-Ser-protein phosphatase activity, whereas it unaffects Ser/Thr-protein kinase activity (casein kinases CKI and CKII), thus promoting a marked increase of the endogenous Ser-phosphorylation level of membrane proteins, such as cytoskeletal spectrin beta-subunit (band 2) and transmembrane band 3 protein. By contrast, the Tyr-phosphorylation state of band 3 protein is practically unaffected by okadaic acid, being unaffected both Tyr-protein kinase and P-Tyr-protein phosphatase activities.