64 Biochimica et Biophysica Acta, 392 (1975) 64--74 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands BBA 27643 ADENOSINE 3',5'-MONOPHOSPHATE DEPENDENT PHOSPHORYLATION OF RIBOSOMES AND RIBOSOMAL SUBUNITS FROM BOVINE CORPUS LUTEUM SALMAN AZHAR* and K.M. JAYARAM MENON** Reproductive Endocrinology Program, Departments of Obstetrics and Gynecology and Biological Chemistry, The University of Michigan Medical Center, Ann Arbor, Mich. 48104 (U.S.A.) (Received November 4th, 1974) Summary In a previous publication the purification and properties of two protein kinases (KI and KII) from a soluble fraction of bovine corpus luteum and the stimulation of the latter fraction by cyclic AMP and luteinizing hormone was reported (Menon, K.M.J. (1973) J. Biol. Chem. 248, 494--501). We have now studied the effects of cyclic AMP and luteinizing hormone on ribosomal pro- tein phosphorylation of corpus luteum by protein kinase II. Protein kinase II catalyzed the phosphorylation of ribosomes by transfer of terminal phosphate of ATP to ribosomal proteins. Extraction with hot trichloroacetic acid and non-aqueous solvent revealed that about 80% of total radioactivity incorpo- rated remain associated with the protein residue. Radioactivity was identified in the phosphoserine and phosphothreonine residues of polypeptides by high voltage paper electrophoresis. The extent of phosphorylation was stimulated by cyclic AMP but not by luteinizing hormone. At least 9 proteins of 80-S ribo- somes and 12 proteins of the 60-S ribosomal subunit were phosphorylated in the presence of cyclic AMP as resolved by urea polyacrylamide gel electro- phoresis. However, only one major and four minor bands were phosphorylated in the case of 40-S ribosomal subunit under the influence of cyclic AMP. The ribosomal protein phosphorylation catalyzed by protein kinase II is regulated by cyclic AMP whereas luteinizing hormone has no effect on ribosome phos- phorylation. Introduction Adenosine 3',5'-monophosphate (cyclic AMP) has been shown to be a * Population Council Postdoctoral Fellow. ** To whom correspondence should he addressed.