Isolation and Properties of Two Protein Kinases from Yeast which Phosphorylate Casein and Some Ribosomal Proteins

Abstract

Three fractions of protein kinase from postribosomal supernatant of Saccharomyces cerevisiae, active in phosphorylation of casein, were resolved on DEAE-cellulose. Two of these fractions: protein kinase 1 and protein kinase 3, were further purified about 1000 and 1800-fold respectively. The kinase 1 appeared to exist as a monomer with a molecular weight of 50 000 and utilized only ATP as phosphoryl donor. The protein kinase 3 was an aggregated form of enzyme with a molecular weight of above half a million and used both ATP and GTP for protein phosphorylation. Both isolated enzymes showed variations in respect to Michaelis constants, and inhibitory effects exerted by monovalent cations and nucleotide phosphates. The activity of the kinases was not affected by the presence of cAMP (adenosine 3′:5′-monophosphate) or cGMP, however, only protein kinase 1 appeared to be a cAMP nucleotide-independent enzyme. Despite these differences both enzymes equally phosphorylated two strongly acidic proteins of the 60-S ribosome subunit, possibly related to L7, L12 of Escherichia coli.