title: A ribosomal protein S6 kinase copurifies with phosphatase-1 activating factor.
abstract: A highly purified preparation of phosphatase-activating kinase (Fa) from rabbit skeletal muscle phosphorylated ribosomal protein S6. The two activities copurified on DEAE-Sephadex, CM-Sephadex, and phosphocellulose chromatography and upon further chromatography on Sephacryl S-300 and FPLC Mono-S and Mono-Q columns. On the latter column, two separate peaks of Fa activity were observed when it was developed in Tris buffer as opposed to beta-glycerophosphate. S6 kinase activity was obtained only with the Fa which adhered to the resin. The Mr of the Fa and S6 activities was determined to be 83,200 by gel permeation on a Sephacryl S-300 column. The Fa preparation phosphorylated serine residues on S6; two tryptic phosphopeptides, A and C, were identified by two-dimensional phosphopeptide analysis. The enzyme also showed good activity toward initiation factor eIF-4B. Based on specificity toward ribosomal proteins and initiation factors, the Fa and a mitogen-stimulated S6 kinase purified from insulin-stimulated 3T3-L1 cells were similar. These results suggest that a form of Fa and an insulin-stimulated S6 kinase may be related or closely associated.
authors.affiliation: Department of Anatomy and Physiology, California State University, Long Beach 90840-3701.
authors.forename: B S
authors.initials: BS
authors.lastname: Khatra
authors.forename: O
authors.initials: O
authors.lastname: Nguyen
authors.forename: P T
authors.initials: PT
authors.lastname: Tuazon
authors.forename: C
authors.initials: C
authors.lastname: DeVack
authors.forename: J A
authors.initials: JA
authors.lastname: Traugh
mesh_terms: D000818:Animals; D002845:Chromatography; D004789:Enzyme Activation; D008970:Molecular Weight; D009132:Muscles / Q000201:enzymology; D010449:Peptide Mapping; D011494:Protein Kinases / Q000302:isolation & purification* / Q000378:metabolism; D011817:Rabbits; D038601:Ribosomal Protein S6; D019893:Ribosomal Protein S6 Kinases; D012269:Ribosomal Proteins / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; D011494:Protein Kinases; C045455:phosphatase-1 kinase; D019893:Ribosomal Protein S6 Kinases