Hepatic protein kinase-C and protein phosphatase type-2A in the fetal rat.
The Ca2(+)- and phospholipid-dependent protein kinase, protein kinase-C (PK-C), was studied in fetal rat liver between d 17 and 21 of gestation. Initial studies showed that rat liver, membrane-associated PK-C could be detected as a protein of Mr = 80,000 using a polyclonal rat brain PK-C antiserum. Fetal hepatic membrane-bound PK-C activity rose as gestation progressed with adult levels (21 +/- 3 pmol/min/mg protein) being attained by term. Although fasting for 48 h led to PK-C activation in adult livers, fetal hepatic PK-C was not activated by 48 h of maternal fasting. Membrane-associated protein phosphatase activity that might reverse PK-C action was also studied. PK-C sites in casein (an artificial PK-C substrate) were selectively dephosphorylated by a membrane-associated, poly-cation-stimulated protein phosphatase. This activity, thus classified as protein phosphatase type-2A, was constitutively expressed in fetal liver membranes from 17-21 d gestation. We have previously reported that the other major hepatic protein phosphatase, protein phosphatase type-1, also is constitutively expressed during the later stage of gestation. Taken together with the results of our present study, our data indicate that PK-C-dependent phosphorylation in fetal liver probably increases with advancing gestation.
Gruppuso
P A
PA
Division of Biology and Medicine, Brown University, Providence, Rhode Island.
D000818:Animals; D001665:Binding Sites; D005333:Fetus / Q000201:enzymology*; D005865:Gestational Age; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases