Vitamin A acid-induced activation of Ca2+-activated, phospholipid-dependent protein kinase from rabbit retina.

Ca2+-activated, phospholipid-dependent protein kinase from rabbit retina was partially purified. Vitamin A acid (retinoic acid) stimulated this protein kinase in the presence of Ca2+, while other metabolites of vitamin A such as retinol or retinal were less effective. The order of the extent of phosphorylation of the various substrate proteins by this protein kinase was identical in the presence of vitamin A acid or phosphatidylserine. The major spots of the 32P labeled peptide from histone H1 phosphorylated in the presence of vitamin A acid by this protein kinase did not differ from those obtained from histone H1 phosphorylated in the presence of phosphatidylserine. Retinol caused a further enhancement of the enzymatic activity, whereas the addition of retinal inhibited the activation by vitamin A acid. Thus, vitamin A and its metabolites may play an important role in the regulation of Ca2+-activated, phospholipid-dependent protein kinase activity in the retina.