[Cancer-associated alterations of human hepatocellular carcinoma beta-glucuronidase--study on phosphorylation by 3', 5'-cyclic AMP dependent-protein kinase].
beta-Glucuronidase purified from human hepatocellular carcinoma consisted of a major subunit with molecular weight of 64,000 (64K-Da) and a minor 76K-Da subunit, whereas the hydrolase from normal liver had almost exclusively 64K-Da subunit. beta-Glucuronidase from the hepatoma and normal liver could serve as a substrate for a cAMP-dependent protein kinase. The rate of phosphorylation reaction of the hepatoma beta-glucuronidase was rapid, whereas that of the normal liver beta-glucuronidase was slow and much lower. Stoichiometry of beta-glucuronidase was 4.3 mol and 0.46 mol of phosphate per mol of the beta-glucuronidase from the hepatoma and normal liver, respectively. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of 32P-labeled beta-glucuronidase indicated that the 64K-dalton subunit was phosphorylated both in hepatoma and normal liver beta-glucuronidase. Tryptic peptide mapping of 32P-labeled beta-glucuronidase from hepatoma identified two distinct phosphopeptides (X and Y). The peptide from hepatoma hydrolase was phosphorylated predominantly at the X, while the peptide Y was the major phosphopeptide in the hydrolase of normal liver. Two-dimensional analysis of phosphoamino acids revealed two sites, phosphoserine and phosphothreonine.
Ono
M
M
Biochemical Laboratory, Hokkaido University School of Medicine, Sapporo.
D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D005966:Glucuronidase / Q000302:isolation & purification*; D006801:Humans; D008099:Liver / Q000201:enzymology; D008113:Liver Neoplasms / Q000201:enzymology*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D013274:Stomach Neoplasms / Q000201:enzymology
D011494:Protein Kinases; D005966:Glucuronidase