Glutathione S-transferase is an in vitro substrate of Ca++-phospholipid-dependent protein kinase (protein kinase C).

Glutathione S-transferase was found to be a good substrate of Ca++-phospholipid-dependent protein kinase in vitro. Of 6 isozymes of glutathione transferase purified from rat liver cytosol (1-1, 1-2, 2-2, 3-3, 3-4, 4-4), only isozymes 1-1, 1-2 and 2-2 were significantly phosphorylated by the kinase purified from rabbit brain. Phosphorylation was more pronounced in subunit 1 than in subunit 2, and the degree of the phosphorylation was similar in all three homo- and heterodimers, where 1 mol of phosphoryl group per mol subunit was transferred to the subunit 1. The phosphorylated transferase 1-1 showed decreased affinity for bilirubin, suggesting that the phosphorylation affects the function of glutathione S-transferase in an isozyme-specific manner.