title: Subunit-specific phosphorylation of pyruvate kinase in medullary thyroid carcinomas of the rat.
abstract: Pyruvate kinase from anaplastic medullary thyroid carcinomas contains predominantly K-type subunits, whereas pyruvate kinase from differentiated medullary thyroid carcinomas consist of M- and K-type subunits in about equal proportion. In order to analyse the incorporation of phosphate in the respective isozymes after endogenous phosphorylation of cytosolic extracts with [32P]ATP, homotetrameric isozymes as well as heterotetrameric hybrids of differentiated tumors were resolved by affinity chromatography on Blue-Sepharose CL-6B and, if necessary, further purified by immunoprecipitation. SDS-polyacrylamide gel electrophoresis of purified isozymes and subsequent autoradiography showed the incorporation of phosphate in the K4-type isozymes, but not in the other isozymes. The phosphorylation appeared to be cAMP-independent and occurred on a serine residue.
authors.affiliation: University Hospital Utrecht, Department of Hematology, The Netherlands.
authors.forename: G
authors.initials: G
authors.lastname: Rijksen
authors.forename: M C
authors.initials: MC
authors.lastname: van der Heijden
authors.forename: R
authors.initials: R
authors.lastname: Oskam
authors.forename: G E
authors.initials: GE
authors.lastname: Staal
mesh_terms: D000818:Animals; D002277:Carcinoma / Q000201:enzymology*; D002846:Chromatography, Affinity; D004588:Electrophoresis, Cellulose Acetate; D004591:Electrophoresis, Polyacrylamide Gel; D007118:Immunoassay; D007163:Immunosorbent Techniques; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D046911:Macromolecular Substances; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D055503:Protein Multimerization; D011770:Pyruvate Kinase / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D013964:Thyroid Neoplasms / Q000201:enzymology*
chemical_list: D007527:Isoenzymes; D046911:Macromolecular Substances; D010710:Phosphates; D011770:Pyruvate Kinase